crypto/async_tx/async_raid6_recov.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * Asynchronous RAID-6 recovery calculations ASYNC_TX API.
  * Copyright(c) 2009 Intel Corporation
  *
  * based on raid6recov.c:
  *   Copyright 2002 H. Peter Anvin
  */
 #include <linux/kernel.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/dma-mapping.h>
 #include <linux/raid/pq.h>
 #include <linux/async_tx.h>
 #include <linux/dmaengine.h>

 static struct dma_async_tx_descriptor *
 async_sum_product(struct page *dest, unsigned int d_off,
 		struct page **srcs, unsigned int *src_offs, unsigned char *coef,
 		size_t len, struct async_submit_ctl *submit)
 {
 	struct dma_chan *chan = async_tx_find_channel(submit, DMA_PQ,
 						      &dest, 1, srcs, 2, len);
 	struct dma_device *dma = chan ? chan->device : NULL;
 	struct dmaengine_unmap_data *unmap = NULL;
 	const u8 *amul, *bmul;
 	u8 ax, bx;
 	u8 *a, *b, *c;

 	if (dma)
 		unmap = dmaengine_get_unmap_data(dma->dev, 3, GFP_NOWAIT);

 	if (unmap) {
 		struct device *dev = dma->dev;
 		dma_addr_t pq[2];
 		struct dma_async_tx_descriptor *tx;
 		enum dma_ctrl_flags dma_flags = DMA_PREP_PQ_DISABLE_P;

 		if (submit->flags & ASYNC_TX_FENCE)
 			dma_flags |= DMA_PREP_FENCE;
 		unmap->addr[0] = dma_map_page(dev, srcs[0], src_offs[0],
 						len, DMA_TO_DEVICE);
 		unmap->addr[1] = dma_map_page(dev, srcs[1], src_offs[1],
 						len, DMA_TO_DEVICE);
 		unmap->to_cnt = 2;

 		unmap->addr[2] = dma_map_page(dev, dest, d_off,
 						len, DMA_BIDIRECTIONAL);
 		unmap->bidi_cnt = 1;
 		/* engine only looks at Q, but expects it to follow P */
 		pq[1] = unmap->addr[2];

 		unmap->len = len;
 		tx = dma->device_prep_dma_pq(chan, pq, unmap->addr, 2, coef,
 					     len, dma_flags);
 		if (tx) {
 			dma_set_unmap(tx, unmap);
 			async_tx_submit(chan, tx, submit);
 			dmaengine_unmap_put(unmap);
 			return tx;
 		}

 		/* could not get a descriptor, unmap and fall through to
 		 * the synchronous path
 		 */
 		dmaengine_unmap_put(unmap);
 	}

 	/* run the operation synchronously */
 	async_tx_quiesce(&submit->depend_tx);
 	amul = raid6_gfmul[coef[0]];
 	bmul = raid6_gfmul[coef[1]];
 	a = page_address(srcs[0]) + src_offs[0];
 	b = page_address(srcs[1]) + src_offs[1];
 	c = page_address(dest) + d_off;

 	while (len--) {
 		ax    = amul[*a++];
 		bx    = bmul[*b++];
 		*c++ = ax ^ bx;
 	}

 	return NULL;
 }

 static struct dma_async_tx_descriptor *
 async_mult(struct page *dest, unsigned int d_off, struct page *src,
 		unsigned int s_off, u8 coef, size_t len,
 		struct async_submit_ctl *submit)
 {
 	struct dma_chan *chan = async_tx_find_channel(submit, DMA_PQ,
 						      &dest, 1, &src, 1, len);
 	struct dma_device *dma = chan ? chan->device : NULL;
 	struct dmaengine_unmap_data *unmap = NULL;
 	const u8 *qmul; /* Q multiplier table */
 	u8 *d, *s;

 	if (dma)
 		unmap = dmaengine_get_unmap_data(dma->dev, 3, GFP_NOWAIT);

 	if (unmap) {
 		dma_addr_t dma_dest[2];
 		struct device *dev = dma->dev;
 		struct dma_async_tx_descriptor *tx;
 		enum dma_ctrl_flags dma_flags = DMA_PREP_PQ_DISABLE_P;

 		if (submit->flags & ASYNC_TX_FENCE)
 			dma_flags |= DMA_PREP_FENCE;
 		unmap->addr[0] = dma_map_page(dev, src, s_off,
 						len, DMA_TO_DEVICE);
 		unmap->to_cnt++;
 		unmap->addr[1] = dma_map_page(dev, dest, d_off,
 						len, DMA_BIDIRECTIONAL);
 		dma_dest[1] = unmap->addr[1];
 		unmap->bidi_cnt++;
 		unmap->len = len;

 		/* this looks funny, but the engine looks for Q at
 		 * dma_dest[1] and ignores dma_dest[0] as a dest
 		 * due to DMA_PREP_PQ_DISABLE_P
 		 */
 		tx = dma->device_prep_dma_pq(chan, dma_dest, unmap->addr,
 					     1, &coef, len, dma_flags);

 		if (tx) {
 			dma_set_unmap(tx, unmap);
 			dmaengine_unmap_put(unmap);
 			async_tx_submit(chan, tx, submit);
 			return tx;
 		}

 		/* could not get a descriptor, unmap and fall through to
 		 * the synchronous path
 		 */
 		dmaengine_unmap_put(unmap);
 	}

 	/* no channel available, or failed to allocate a descriptor, so
 	 * perform the operation synchronously
 	 */
 	async_tx_quiesce(&submit->depend_tx);
 	qmul  = raid6_gfmul[coef];
 	d = page_address(dest) + d_off;
 	s = page_address(src) + s_off;

 	while (len--)
 		*d++ = qmul[*s++];

 	return NULL;
 }

 static struct dma_async_tx_descriptor *
 __2data_recov_4(int disks, size_t bytes, int faila, int failb,
 		struct page **blocks, unsigned int *offs,
 		struct async_submit_ctl *submit)
 {
 	struct dma_async_tx_descriptor *tx = NULL;
 	struct page *p, *q, *a, *b;
 	unsigned int p_off, q_off, a_off, b_off;
 	struct page *srcs[2];
 	unsigned int src_offs[2];
 	unsigned char coef[2];
 	enum async_tx_flags flags = submit->flags;
 	dma_async_tx_callback cb_fn = submit->cb_fn;
 	void *cb_param = submit->cb_param;
 	void *scribble = submit->scribble;

 	p = blocks[disks-2];
 	p_off = offs[disks-2];
 	q = blocks[disks-1];
 	q_off = offs[disks-1];

 	a = blocks[faila];
 	a_off = offs[faila];
 	b = blocks[failb];
 	b_off = offs[failb];

 	/* in the 4 disk case P + Pxy == P and Q + Qxy == Q */
 	/* Dx = A*(P+Pxy) + B*(Q+Qxy) */
 	srcs[0] = p;
 	src_offs[0] = p_off;
 	srcs[1] = q;
 	src_offs[1] = q_off;
 	coef[0] = raid6_gfexi[failb-faila];
 	coef[1] = raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]];
 	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_sum_product(b, b_off, srcs, src_offs, coef, bytes, submit);

 	/* Dy = P+Pxy+Dx */
 	srcs[0] = p;
 	src_offs[0] = p_off;
 	srcs[1] = b;
 	src_offs[1] = b_off;
 	init_async_submit(submit, flags | ASYNC_TX_XOR_ZERO_DST, tx, cb_fn,
 			  cb_param, scribble);
 	tx = async_xor_offs(a, a_off, srcs, src_offs, 2, bytes, submit);

 	return tx;

 }

 static struct dma_async_tx_descriptor *
 __2data_recov_5(int disks, size_t bytes, int faila, int failb,
 		struct page **blocks, unsigned int *offs,
 		struct async_submit_ctl *submit)
 {
 	struct dma_async_tx_descriptor *tx = NULL;
 	struct page *p, *q, *g, *dp, *dq;
 	unsigned int p_off, q_off, g_off, dp_off, dq_off;
 	struct page *srcs[2];
 	unsigned int src_offs[2];
 	unsigned char coef[2];
 	enum async_tx_flags flags = submit->flags;
 	dma_async_tx_callback cb_fn = submit->cb_fn;
 	void *cb_param = submit->cb_param;
 	void *scribble = submit->scribble;
 	int good_srcs, good, i;

 	good_srcs = 0;
 	good = -1;
 	for (i = 0; i < disks-2; i++) {
 		if (blocks[i] == NULL)
 			continue;
 		if (i == faila || i == failb)
 			continue;
 		good = i;
 		good_srcs++;
 	}
 	BUG_ON(good_srcs > 1);

 	p = blocks[disks-2];
 	p_off = offs[disks-2];
 	q = blocks[disks-1];
 	q_off = offs[disks-1];
 	g = blocks[good];
 	g_off = offs[good];

 	/* Compute syndrome with zero for the missing data pages
 	 * Use the dead data pages as temporary storage for delta p and
 	 * delta q
 	 */
 	dp = blocks[faila];
 	dp_off = offs[faila];
 	dq = blocks[failb];
 	dq_off = offs[failb];

 	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_memcpy(dp, g, dp_off, g_off, bytes, submit);
 	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_mult(dq, dq_off, g, g_off,
 			raid6_gfexp[good], bytes, submit);

 	/* compute P + Pxy */
 	srcs[0] = dp;
 	src_offs[0] = dp_off;
 	srcs[1] = p;
 	src_offs[1] = p_off;
 	init_async_submit(submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
 			  NULL, NULL, scribble);
 	tx = async_xor_offs(dp, dp_off, srcs, src_offs, 2, bytes, submit);

 	/* compute Q + Qxy */
 	srcs[0] = dq;
 	src_offs[0] = dq_off;
 	srcs[1] = q;
 	src_offs[1] = q_off;
 	init_async_submit(submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
 			  NULL, NULL, scribble);
 	tx = async_xor_offs(dq, dq_off, srcs, src_offs, 2, bytes, submit);

 	/* Dx = A*(P+Pxy) + B*(Q+Qxy) */
 	srcs[0] = dp;
 	src_offs[0] = dp_off;
 	srcs[1] = dq;
 	src_offs[1] = dq_off;
 	coef[0] = raid6_gfexi[failb-faila];
 	coef[1] = raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]];
 	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_sum_product(dq, dq_off, srcs, src_offs, coef, bytes, submit);

 	/* Dy = P+Pxy+Dx */
 	srcs[0] = dp;
 	src_offs[0] = dp_off;
 	srcs[1] = dq;
 	src_offs[1] = dq_off;
 	init_async_submit(submit, flags | ASYNC_TX_XOR_DROP_DST, tx, cb_fn,
 			  cb_param, scribble);
 	tx = async_xor_offs(dp, dp_off, srcs, src_offs, 2, bytes, submit);

 	return tx;
 }

 static struct dma_async_tx_descriptor *
 __2data_recov_n(int disks, size_t bytes, int faila, int failb,
 	      struct page **blocks, unsigned int *offs,
 		  struct async_submit_ctl *submit)
 {
 	struct dma_async_tx_descriptor *tx = NULL;
 	struct page *p, *q, *dp, *dq;
 	unsigned int p_off, q_off, dp_off, dq_off;
 	struct page *srcs[2];
 	unsigned int src_offs[2];
 	unsigned char coef[2];
 	enum async_tx_flags flags = submit->flags;
 	dma_async_tx_callback cb_fn = submit->cb_fn;
 	void *cb_param = submit->cb_param;
 	void *scribble = submit->scribble;

 	p = blocks[disks-2];
 	p_off = offs[disks-2];
 	q = blocks[disks-1];
 	q_off = offs[disks-1];

 	/* Compute syndrome with zero for the missing data pages
 	 * Use the dead data pages as temporary storage for
 	 * delta p and delta q
 	 */
 	dp = blocks[faila];
 	dp_off = offs[faila];
 	blocks[faila] = NULL;
 	blocks[disks-2] = dp;
 	offs[disks-2] = dp_off;
 	dq = blocks[failb];
 	dq_off = offs[failb];
 	blocks[failb] = NULL;
 	blocks[disks-1] = dq;
 	offs[disks-1] = dq_off;

 	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_gen_syndrome(blocks, offs, disks, bytes, submit);

 	/* Restore pointer table */
 	blocks[faila]   = dp;
 	offs[faila] = dp_off;
 	blocks[failb]   = dq;
 	offs[failb] = dq_off;
 	blocks[disks-2] = p;
 	offs[disks-2] = p_off;
 	blocks[disks-1] = q;
 	offs[disks-1] = q_off;

 	/* compute P + Pxy */
 	srcs[0] = dp;
 	src_offs[0] = dp_off;
 	srcs[1] = p;
 	src_offs[1] = p_off;
 	init_async_submit(submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
 			  NULL, NULL, scribble);
 	tx = async_xor_offs(dp, dp_off, srcs, src_offs, 2, bytes, submit);

 	/* compute Q + Qxy */
 	srcs[0] = dq;
 	src_offs[0] = dq_off;
 	srcs[1] = q;
 	src_offs[1] = q_off;
 	init_async_submit(submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
 			  NULL, NULL, scribble);
 	tx = async_xor_offs(dq, dq_off, srcs, src_offs, 2, bytes, submit);

 	/* Dx = A*(P+Pxy) + B*(Q+Qxy) */
 	srcs[0] = dp;
 	src_offs[0] = dp_off;
 	srcs[1] = dq;
 	src_offs[1] = dq_off;
 	coef[0] = raid6_gfexi[failb-faila];
 	coef[1] = raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]];
 	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_sum_product(dq, dq_off, srcs, src_offs, coef, bytes, submit);

 	/* Dy = P+Pxy+Dx */
 	srcs[0] = dp;
 	src_offs[0] = dp_off;
 	srcs[1] = dq;
 	src_offs[1] = dq_off;
 	init_async_submit(submit, flags | ASYNC_TX_XOR_DROP_DST, tx, cb_fn,
 			  cb_param, scribble);
 	tx = async_xor_offs(dp, dp_off, srcs, src_offs, 2, bytes, submit);

 	return tx;
 }

 /**
  * async_raid6_2data_recov - asynchronously calculate two missing data blocks
  * @disks: number of disks in the RAID-6 array
  * @bytes: block size
  * @faila: first failed drive index
  * @failb: second failed drive index
  * @blocks: array of source pointers where the last two entries are p and q
  * @offs: array of offset for pages in blocks
  * @submit: submission/completion modifiers
  */
 struct dma_async_tx_descriptor *
 async_raid6_2data_recov(int disks, size_t bytes, int faila, int failb,
 			struct page **blocks, unsigned int *offs,
 			struct async_submit_ctl *submit)
 {
 	void *scribble = submit->scribble;
 	int non_zero_srcs, i;

 	BUG_ON(faila == failb);
 	if (failb < faila)
 		swap(faila, failb);

 	pr_debug("%s: disks: %d len: %zu\n", __func__, disks, bytes);

 	/* if a dma resource is not available or a scribble buffer is not
 	 * available punt to the synchronous path.  In the 'dma not
 	 * available' case be sure to use the scribble buffer to
 	 * preserve the content of 'blocks' as the caller intended.
 	 */
 	if (!async_dma_find_channel(DMA_PQ) || !scribble) {
 		void **ptrs = scribble ? scribble : (void **) blocks;

 		async_tx_quiesce(&submit->depend_tx);
 		for (i = 0; i < disks; i++)
 			if (blocks[i] == NULL)
 				ptrs[i] = (void *) raid6_empty_zero_page;
 			else
 				ptrs[i] = page_address(blocks[i]) + offs[i];

 		raid6_2data_recov(disks, bytes, faila, failb, ptrs);

 		async_tx_sync_epilog(submit);

 		return NULL;
 	}

 	non_zero_srcs = 0;
 	for (i = 0; i < disks-2 && non_zero_srcs < 4; i++)
 		if (blocks[i])
 			non_zero_srcs++;
 	switch (non_zero_srcs) {
 	case 0:
 	case 1:
 		/* There must be at least 2 sources - the failed devices. */
 		BUG();

 	case 2:
 		/* dma devices do not uniformly understand a zero source pq
 		 * operation (in contrast to the synchronous case), so
 		 * explicitly handle the special case of a 4 disk array with
 		 * both data disks missing.
 		 */
 		return __2data_recov_4(disks, bytes, faila, failb,
 				blocks, offs, submit);
 	case 3:
 		/* dma devices do not uniformly understand a single
 		 * source pq operation (in contrast to the synchronous
 		 * case), so explicitly handle the special case of a 5 disk
 		 * array with 2 of 3 data disks missing.
 		 */
 		return __2data_recov_5(disks, bytes, faila, failb,
 				blocks, offs, submit);
 	default:
 		return __2data_recov_n(disks, bytes, faila, failb,
 				blocks, offs, submit);
 	}
 }
 EXPORT_SYMBOL_GPL(async_raid6_2data_recov);

 /**
  * async_raid6_datap_recov - asynchronously calculate a data and the 'p' block
  * @disks: number of disks in the RAID-6 array
  * @bytes: block size
  * @faila: failed drive index
  * @blocks: array of source pointers where the last two entries are p and q
  * @offs: array of offset for pages in blocks
  * @submit: submission/completion modifiers
  */
 struct dma_async_tx_descriptor *
 async_raid6_datap_recov(int disks, size_t bytes, int faila,
 			struct page **blocks, unsigned int *offs,
 			struct async_submit_ctl *submit)
 {
 	struct dma_async_tx_descriptor *tx = NULL;
 	struct page *p, *q, *dq;
 	unsigned int p_off, q_off, dq_off;
 	u8 coef;
 	enum async_tx_flags flags = submit->flags;
 	dma_async_tx_callback cb_fn = submit->cb_fn;
 	void *cb_param = submit->cb_param;
 	void *scribble = submit->scribble;
 	int good_srcs, good, i;
 	struct page *srcs[2];
 	unsigned int src_offs[2];

 	pr_debug("%s: disks: %d len: %zu\n", __func__, disks, bytes);

 	/* if a dma resource is not available or a scribble buffer is not
 	 * available punt to the synchronous path.  In the 'dma not
 	 * available' case be sure to use the scribble buffer to
 	 * preserve the content of 'blocks' as the caller intended.
 	 */
 	if (!async_dma_find_channel(DMA_PQ) || !scribble) {
 		void **ptrs = scribble ? scribble : (void **) blocks;

 		async_tx_quiesce(&submit->depend_tx);
 		for (i = 0; i < disks; i++)
 			if (blocks[i] == NULL)
 				ptrs[i] = (void*)raid6_empty_zero_page;
 			else
 				ptrs[i] = page_address(blocks[i]) + offs[i];

 		raid6_datap_recov(disks, bytes, faila, ptrs);

 		async_tx_sync_epilog(submit);

 		return NULL;
 	}

 	good_srcs = 0;
 	good = -1;
 	for (i = 0; i < disks-2; i++) {
 		if (i == faila)
 			continue;
 		if (blocks[i]) {
 			good = i;
 			good_srcs++;
 			if (good_srcs > 1)
 				break;
 		}
 	}
 	BUG_ON(good_srcs == 0);

 	p = blocks[disks-2];
 	p_off = offs[disks-2];
 	q = blocks[disks-1];
 	q_off = offs[disks-1];

 	/* Compute syndrome with zero for the missing data page
 	 * Use the dead data page as temporary storage for delta q
 	 */
 	dq = blocks[faila];
 	dq_off = offs[faila];
 	blocks[faila] = NULL;
 	blocks[disks-1] = dq;
 	offs[disks-1] = dq_off;

 	/* in the 4-disk case we only need to perform a single source
 	 * multiplication with the one good data block.
 	 */
 	if (good_srcs == 1) {
 		struct page *g = blocks[good];
 		unsigned int g_off = offs[good];

 		init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL,
 				  scribble);
 		tx = async_memcpy(p, g, p_off, g_off, bytes, submit);

 		init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL,
 				  scribble);
 		tx = async_mult(dq, dq_off, g, g_off,
 				raid6_gfexp[good], bytes, submit);
 	} else {
 		init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL,
 				  scribble);
 		tx = async_gen_syndrome(blocks, offs, disks, bytes, submit);
 	}

 	/* Restore pointer table */
 	blocks[faila]   = dq;
 	offs[faila] = dq_off;
 	blocks[disks-1] = q;
 	offs[disks-1] = q_off;

 	/* calculate g^{-faila} */
 	coef = raid6_gfinv[raid6_gfexp[faila]];

 	srcs[0] = dq;
 	src_offs[0] = dq_off;
 	srcs[1] = q;
 	src_offs[1] = q_off;
 	init_async_submit(submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
 			  NULL, NULL, scribble);
 	tx = async_xor_offs(dq, dq_off, srcs, src_offs, 2, bytes, submit);

 	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_mult(dq, dq_off, dq, dq_off, coef, bytes, submit);

 	srcs[0] = p;
 	src_offs[0] = p_off;
 	srcs[1] = dq;
 	src_offs[1] = dq_off;
 	init_async_submit(submit, flags | ASYNC_TX_XOR_DROP_DST, tx, cb_fn,
 			  cb_param, scribble);
 	tx = async_xor_offs(p, p_off, srcs, src_offs, 2, bytes, submit);

 	return tx;
 }
 EXPORT_SYMBOL_GPL(async_raid6_datap_recov);

 MODULE_AUTHOR("Dan Williams <dan.j.williams@intel.com>");
 MODULE_DESCRIPTION("asynchronous RAID-6 recovery api");
 MODULE_LICENSE("GPL");
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* Asynchronous RAID-6 recovery calculations ASYNC_TX API.
	* Copyright(c) 2009 Intel Corporation
	*
	* based on raid6recov.c:
	* Copyright 2002 H. Peter Anvin
	*/
	#include <linux/kernel.h>
	#include <linux/interrupt.h>
	#include <linux/module.h>
	#include <linux/dma-mapping.h>
	#include <linux/raid/pq.h>
	#include <linux/async_tx.h>
	#include <linux/dmaengine.h>

	static struct dma_async_tx_descriptor *
	async_sum_product(struct page *dest, unsigned int d_off,
	struct page *srcs, unsigned int src_offs, unsigned char *coef,
	size_t len, struct async_submit_ctl *submit)
	{
	struct dma_chan *chan = async_tx_find_channel(submit, DMA_PQ,
	&dest, 1, srcs, 2, len);
	struct dma_device *dma = chan ? chan->device : NULL;
	struct dmaengine_unmap_data *unmap = NULL;
	const u8 amul, bmul;
	u8 ax, bx;
	u8 a, b, *c;

	if (dma)
	unmap = dmaengine_get_unmap_data(dma->dev, 3, GFP_NOWAIT);

	if (unmap) {
	struct device *dev = dma->dev;
	dma_addr_t pq[2];
	struct dma_async_tx_descriptor *tx;
	enum dma_ctrl_flags dma_flags = DMA_PREP_PQ_DISABLE_P;

	if (submit->flags & ASYNC_TX_FENCE)
	dma_flags \|= DMA_PREP_FENCE;
	unmap->addr[0] = dma_map_page(dev, srcs[0], src_offs[0],
	len, DMA_TO_DEVICE);
	unmap->addr[1] = dma_map_page(dev, srcs[1], src_offs[1],
	len, DMA_TO_DEVICE);
	unmap->to_cnt = 2;

	unmap->addr[2] = dma_map_page(dev, dest, d_off,
	len, DMA_BIDIRECTIONAL);
	unmap->bidi_cnt = 1;
	/* engine only looks at Q, but expects it to follow P */
	pq[1] = unmap->addr[2];

	unmap->len = len;
	tx = dma->device_prep_dma_pq(chan, pq, unmap->addr, 2, coef,
	len, dma_flags);
	if (tx) {
	dma_set_unmap(tx, unmap);
	async_tx_submit(chan, tx, submit);
	dmaengine_unmap_put(unmap);
	return tx;
	}

	/* could not get a descriptor, unmap and fall through to
	* the synchronous path
	*/
	dmaengine_unmap_put(unmap);
	}

	/* run the operation synchronously */
	async_tx_quiesce(&submit->depend_tx);
	amul = raid6_gfmul[coef[0]];
	bmul = raid6_gfmul[coef[1]];
	a = page_address(srcs[0]) + src_offs[0];
	b = page_address(srcs[1]) + src_offs[1];
	c = page_address(dest) + d_off;

	while (len--) {
	ax = amul[*a++];
	bx = bmul[*b++];
	*c++ = ax ^ bx;
	}

	return NULL;
	}

	static struct dma_async_tx_descriptor *
	async_mult(struct page dest, unsigned int d_off, struct page src,
	unsigned int s_off, u8 coef, size_t len,
	struct async_submit_ctl *submit)
	{
	struct dma_chan *chan = async_tx_find_channel(submit, DMA_PQ,
	&dest, 1, &src, 1, len);
	struct dma_device *dma = chan ? chan->device : NULL;
	struct dmaengine_unmap_data *unmap = NULL;
	const u8 qmul; / Q multiplier table */
	u8 d, s;

	if (dma)
	unmap = dmaengine_get_unmap_data(dma->dev, 3, GFP_NOWAIT);

	if (unmap) {
	dma_addr_t dma_dest[2];
	struct device *dev = dma->dev;
	struct dma_async_tx_descriptor *tx;
	enum dma_ctrl_flags dma_flags = DMA_PREP_PQ_DISABLE_P;

	if (submit->flags & ASYNC_TX_FENCE)
	dma_flags \|= DMA_PREP_FENCE;
	unmap->addr[0] = dma_map_page(dev, src, s_off,
	len, DMA_TO_DEVICE);
	unmap->to_cnt++;
	unmap->addr[1] = dma_map_page(dev, dest, d_off,
	len, DMA_BIDIRECTIONAL);
	dma_dest[1] = unmap->addr[1];
	unmap->bidi_cnt++;
	unmap->len = len;

	/* this looks funny, but the engine looks for Q at
	* dma_dest[1] and ignores dma_dest[0] as a dest
	* due to DMA_PREP_PQ_DISABLE_P
	*/
	tx = dma->device_prep_dma_pq(chan, dma_dest, unmap->addr,
	1, &coef, len, dma_flags);

	if (tx) {
	dma_set_unmap(tx, unmap);
	dmaengine_unmap_put(unmap);
	async_tx_submit(chan, tx, submit);
	return tx;
	}

	/* could not get a descriptor, unmap and fall through to
	* the synchronous path
	*/
	dmaengine_unmap_put(unmap);
	}

	/* no channel available, or failed to allocate a descriptor, so
	* perform the operation synchronously
	*/
	async_tx_quiesce(&submit->depend_tx);
	qmul = raid6_gfmul[coef];
	d = page_address(dest) + d_off;
	s = page_address(src) + s_off;

	while (len--)
	d++ = qmul[s++];

	return NULL;
	}

	static struct dma_async_tx_descriptor *
	__2data_recov_4(int disks, size_t bytes, int faila, int failb,
	struct page *blocks, unsigned int offs,
	struct async_submit_ctl *submit)
	{
	struct dma_async_tx_descriptor *tx = NULL;
	struct page p, q, a, b;
	unsigned int p_off, q_off, a_off, b_off;
	struct page *srcs[2];
	unsigned int src_offs[2];
	unsigned char coef[2];
	enum async_tx_flags flags = submit->flags;
	dma_async_tx_callback cb_fn = submit->cb_fn;
	void *cb_param = submit->cb_param;
	void *scribble = submit->scribble;

	p = blocks[disks-2];
	p_off = offs[disks-2];
	q = blocks[disks-1];
	q_off = offs[disks-1];

	a = blocks[faila];
	a_off = offs[faila];
	b = blocks[failb];
	b_off = offs[failb];

	/* in the 4 disk case P + Pxy == P and Q + Qxy == Q */
	/* Dx = A(P+Pxy) + B(Q+Qxy) */
	srcs[0] = p;
	src_offs[0] = p_off;
	srcs[1] = q;
	src_offs[1] = q_off;
	coef[0] = raid6_gfexi[failb-faila];
	coef[1] = raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]];
	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
	tx = async_sum_product(b, b_off, srcs, src_offs, coef, bytes, submit);

	/* Dy = P+Pxy+Dx */
	srcs[0] = p;
	src_offs[0] = p_off;
	srcs[1] = b;
	src_offs[1] = b_off;
	init_async_submit(submit, flags \| ASYNC_TX_XOR_ZERO_DST, tx, cb_fn,
	cb_param, scribble);
	tx = async_xor_offs(a, a_off, srcs, src_offs, 2, bytes, submit);

	return tx;

	}

	static struct dma_async_tx_descriptor *
	__2data_recov_5(int disks, size_t bytes, int faila, int failb,
	struct page *blocks, unsigned int offs,
	struct async_submit_ctl *submit)
	{
	struct dma_async_tx_descriptor *tx = NULL;
	struct page p, q, g, dp, *dq;
	unsigned int p_off, q_off, g_off, dp_off, dq_off;
	struct page *srcs[2];
	unsigned int src_offs[2];
	unsigned char coef[2];
	enum async_tx_flags flags = submit->flags;
	dma_async_tx_callback cb_fn = submit->cb_fn;
	void *cb_param = submit->cb_param;
	void *scribble = submit->scribble;
	int good_srcs, good, i;

	good_srcs = 0;
	good = -1;
	for (i = 0; i < disks-2; i++) {
	if (blocks[i] == NULL)
	continue;
	if (i == faila \|\| i == failb)
	continue;
	good = i;
	good_srcs++;
	}
	BUG_ON(good_srcs > 1);

	p = blocks[disks-2];
	p_off = offs[disks-2];
	q = blocks[disks-1];
	q_off = offs[disks-1];
	g = blocks[good];
	g_off = offs[good];

	/* Compute syndrome with zero for the missing data pages
	* Use the dead data pages as temporary storage for delta p and
	* delta q
	*/
	dp = blocks[faila];
	dp_off = offs[faila];
	dq = blocks[failb];
	dq_off = offs[failb];

	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
	tx = async_memcpy(dp, g, dp_off, g_off, bytes, submit);
	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
	tx = async_mult(dq, dq_off, g, g_off,
	raid6_gfexp[good], bytes, submit);

	/* compute P + Pxy */
	srcs[0] = dp;
	src_offs[0] = dp_off;
	srcs[1] = p;
	src_offs[1] = p_off;
	init_async_submit(submit, ASYNC_TX_FENCE\|ASYNC_TX_XOR_DROP_DST, tx,
	NULL, NULL, scribble);
	tx = async_xor_offs(dp, dp_off, srcs, src_offs, 2, bytes, submit);

	/* compute Q + Qxy */
	srcs[0] = dq;
	src_offs[0] = dq_off;
	srcs[1] = q;
	src_offs[1] = q_off;
	init_async_submit(submit, ASYNC_TX_FENCE\|ASYNC_TX_XOR_DROP_DST, tx,
	NULL, NULL, scribble);
	tx = async_xor_offs(dq, dq_off, srcs, src_offs, 2, bytes, submit);

	/* Dx = A(P+Pxy) + B(Q+Qxy) */
	srcs[0] = dp;
	src_offs[0] = dp_off;
	srcs[1] = dq;
	src_offs[1] = dq_off;
	coef[0] = raid6_gfexi[failb-faila];
	coef[1] = raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]];
	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
	tx = async_sum_product(dq, dq_off, srcs, src_offs, coef, bytes, submit);

	/* Dy = P+Pxy+Dx */
	srcs[0] = dp;
	src_offs[0] = dp_off;
	srcs[1] = dq;
	src_offs[1] = dq_off;
	init_async_submit(submit, flags \| ASYNC_TX_XOR_DROP_DST, tx, cb_fn,
	cb_param, scribble);
	tx = async_xor_offs(dp, dp_off, srcs, src_offs, 2, bytes, submit);

	return tx;
	}

	static struct dma_async_tx_descriptor *
	__2data_recov_n(int disks, size_t bytes, int faila, int failb,
	struct page *blocks, unsigned int offs,
	struct async_submit_ctl *submit)
	{
	struct dma_async_tx_descriptor *tx = NULL;
	struct page p, q, dp, dq;
	unsigned int p_off, q_off, dp_off, dq_off;
	struct page *srcs[2];
	unsigned int src_offs[2];
	unsigned char coef[2];
	enum async_tx_flags flags = submit->flags;
	dma_async_tx_callback cb_fn = submit->cb_fn;
	void *cb_param = submit->cb_param;
	void *scribble = submit->scribble;

	p = blocks[disks-2];
	p_off = offs[disks-2];
	q = blocks[disks-1];
	q_off = offs[disks-1];

	/* Compute syndrome with zero for the missing data pages
	* Use the dead data pages as temporary storage for
	* delta p and delta q
	*/
	dp = blocks[faila];
	dp_off = offs[faila];
	blocks[faila] = NULL;
	blocks[disks-2] = dp;
	offs[disks-2] = dp_off;
	dq = blocks[failb];
	dq_off = offs[failb];
	blocks[failb] = NULL;
	blocks[disks-1] = dq;
	offs[disks-1] = dq_off;

	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
	tx = async_gen_syndrome(blocks, offs, disks, bytes, submit);

	/* Restore pointer table */
	blocks[faila] = dp;
	offs[faila] = dp_off;
	blocks[failb] = dq;
	offs[failb] = dq_off;
	blocks[disks-2] = p;
	offs[disks-2] = p_off;
	blocks[disks-1] = q;
	offs[disks-1] = q_off;

	/* compute P + Pxy */
	srcs[0] = dp;
	src_offs[0] = dp_off;
	srcs[1] = p;
	src_offs[1] = p_off;
	init_async_submit(submit, ASYNC_TX_FENCE\|ASYNC_TX_XOR_DROP_DST, tx,
	NULL, NULL, scribble);
	tx = async_xor_offs(dp, dp_off, srcs, src_offs, 2, bytes, submit);

	/* compute Q + Qxy */
	srcs[0] = dq;
	src_offs[0] = dq_off;
	srcs[1] = q;
	src_offs[1] = q_off;
	init_async_submit(submit, ASYNC_TX_FENCE\|ASYNC_TX_XOR_DROP_DST, tx,
	NULL, NULL, scribble);
	tx = async_xor_offs(dq, dq_off, srcs, src_offs, 2, bytes, submit);

	/* Dx = A(P+Pxy) + B(Q+Qxy) */
	srcs[0] = dp;
	src_offs[0] = dp_off;
	srcs[1] = dq;
	src_offs[1] = dq_off;
	coef[0] = raid6_gfexi[failb-faila];
	coef[1] = raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]];
	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
	tx = async_sum_product(dq, dq_off, srcs, src_offs, coef, bytes, submit);

	/* Dy = P+Pxy+Dx */
	srcs[0] = dp;
	src_offs[0] = dp_off;
	srcs[1] = dq;
	src_offs[1] = dq_off;
	init_async_submit(submit, flags \| ASYNC_TX_XOR_DROP_DST, tx, cb_fn,
	cb_param, scribble);
	tx = async_xor_offs(dp, dp_off, srcs, src_offs, 2, bytes, submit);

	return tx;
	}

	/**
	* async_raid6_2data_recov - asynchronously calculate two missing data blocks
	* @disks: number of disks in the RAID-6 array
	* @bytes: block size
	* @faila: first failed drive index
	* @failb: second failed drive index
	* @blocks: array of source pointers where the last two entries are p and q
	* @offs: array of offset for pages in blocks
	* @submit: submission/completion modifiers
	*/
	struct dma_async_tx_descriptor *
	async_raid6_2data_recov(int disks, size_t bytes, int faila, int failb,
	struct page *blocks, unsigned int offs,
	struct async_submit_ctl *submit)
	{
	void *scribble = submit->scribble;
	int non_zero_srcs, i;

	BUG_ON(faila == failb);
	if (failb < faila)
	swap(faila, failb);

	pr_debug("%s: disks: %d len: %zu\n", __func__, disks, bytes);

	/* if a dma resource is not available or a scribble buffer is not
	* available punt to the synchronous path. In the 'dma not
	* available' case be sure to use the scribble buffer to
	* preserve the content of 'blocks' as the caller intended.
	*/
	if (!async_dma_find_channel(DMA_PQ) \|\| !scribble) {
	void ptrs = scribble ? scribble : (void ) blocks;

	async_tx_quiesce(&submit->depend_tx);
	for (i = 0; i < disks; i++)
	if (blocks[i] == NULL)
	ptrs[i] = (void *) raid6_empty_zero_page;
	else
	ptrs[i] = page_address(blocks[i]) + offs[i];

	raid6_2data_recov(disks, bytes, faila, failb, ptrs);

	async_tx_sync_epilog(submit);

	return NULL;
	}

	non_zero_srcs = 0;
	for (i = 0; i < disks-2 && non_zero_srcs < 4; i++)
	if (blocks[i])
	non_zero_srcs++;
	switch (non_zero_srcs) {
	case 0:
	case 1:
	/* There must be at least 2 sources - the failed devices. */
	BUG();

	case 2:
	/* dma devices do not uniformly understand a zero source pq
	* operation (in contrast to the synchronous case), so
	* explicitly handle the special case of a 4 disk array with
	* both data disks missing.
	*/
	return __2data_recov_4(disks, bytes, faila, failb,
	blocks, offs, submit);
	case 3:
	/* dma devices do not uniformly understand a single
	* source pq operation (in contrast to the synchronous
	* case), so explicitly handle the special case of a 5 disk
	* array with 2 of 3 data disks missing.
	*/
	return __2data_recov_5(disks, bytes, faila, failb,
	blocks, offs, submit);
	default:
	return __2data_recov_n(disks, bytes, faila, failb,
	blocks, offs, submit);
	}
	}
	EXPORT_SYMBOL_GPL(async_raid6_2data_recov);

	/**
	* async_raid6_datap_recov - asynchronously calculate a data and the 'p' block
	* @disks: number of disks in the RAID-6 array
	* @bytes: block size
	* @faila: failed drive index
	* @blocks: array of source pointers where the last two entries are p and q
	* @offs: array of offset for pages in blocks
	* @submit: submission/completion modifiers
	*/
	struct dma_async_tx_descriptor *
	async_raid6_datap_recov(int disks, size_t bytes, int faila,
	struct page *blocks, unsigned int offs,
	struct async_submit_ctl *submit)
	{
	struct dma_async_tx_descriptor *tx = NULL;
	struct page p, q, *dq;
	unsigned int p_off, q_off, dq_off;
	u8 coef;
	enum async_tx_flags flags = submit->flags;
	dma_async_tx_callback cb_fn = submit->cb_fn;
	void *cb_param = submit->cb_param;
	void *scribble = submit->scribble;
	int good_srcs, good, i;
	struct page *srcs[2];
	unsigned int src_offs[2];

	pr_debug("%s: disks: %d len: %zu\n", __func__, disks, bytes);

	/* if a dma resource is not available or a scribble buffer is not
	* available punt to the synchronous path. In the 'dma not
	* available' case be sure to use the scribble buffer to
	* preserve the content of 'blocks' as the caller intended.
	*/
	if (!async_dma_find_channel(DMA_PQ) \|\| !scribble) {
	void ptrs = scribble ? scribble : (void ) blocks;

	async_tx_quiesce(&submit->depend_tx);
	for (i = 0; i < disks; i++)
	if (blocks[i] == NULL)
	ptrs[i] = (void*)raid6_empty_zero_page;
	else
	ptrs[i] = page_address(blocks[i]) + offs[i];

	raid6_datap_recov(disks, bytes, faila, ptrs);

	async_tx_sync_epilog(submit);

	return NULL;
	}

	good_srcs = 0;
	good = -1;
	for (i = 0; i < disks-2; i++) {
	if (i == faila)
	continue;
	if (blocks[i]) {
	good = i;
	good_srcs++;
	if (good_srcs > 1)
	break;
	}
	}
	BUG_ON(good_srcs == 0);

	p = blocks[disks-2];
	p_off = offs[disks-2];
	q = blocks[disks-1];
	q_off = offs[disks-1];

	/* Compute syndrome with zero for the missing data page
	* Use the dead data page as temporary storage for delta q
	*/
	dq = blocks[faila];
	dq_off = offs[faila];
	blocks[faila] = NULL;
	blocks[disks-1] = dq;
	offs[disks-1] = dq_off;

	/* in the 4-disk case we only need to perform a single source
	* multiplication with the one good data block.
	*/
	if (good_srcs == 1) {
	struct page *g = blocks[good];
	unsigned int g_off = offs[good];

	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL,
	scribble);
	tx = async_memcpy(p, g, p_off, g_off, bytes, submit);

	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL,
	scribble);
	tx = async_mult(dq, dq_off, g, g_off,
	raid6_gfexp[good], bytes, submit);
	} else {
	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL,
	scribble);
	tx = async_gen_syndrome(blocks, offs, disks, bytes, submit);
	}

	/* Restore pointer table */
	blocks[faila] = dq;
	offs[faila] = dq_off;
	blocks[disks-1] = q;
	offs[disks-1] = q_off;

	/* calculate g^{-faila} */
	coef = raid6_gfinv[raid6_gfexp[faila]];

	srcs[0] = dq;
	src_offs[0] = dq_off;
	srcs[1] = q;
	src_offs[1] = q_off;
	init_async_submit(submit, ASYNC_TX_FENCE\|ASYNC_TX_XOR_DROP_DST, tx,
	NULL, NULL, scribble);
	tx = async_xor_offs(dq, dq_off, srcs, src_offs, 2, bytes, submit);

	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
	tx = async_mult(dq, dq_off, dq, dq_off, coef, bytes, submit);

	srcs[0] = p;
	src_offs[0] = p_off;
	srcs[1] = dq;
	src_offs[1] = dq_off;
	init_async_submit(submit, flags \| ASYNC_TX_XOR_DROP_DST, tx, cb_fn,
	cb_param, scribble);
	tx = async_xor_offs(p, p_off, srcs, src_offs, 2, bytes, submit);

	return tx;
	}
	EXPORT_SYMBOL_GPL(async_raid6_datap_recov);

	MODULE_AUTHOR("Dan Williams <dan.j.williams@intel.com>");
	MODULE_DESCRIPTION("asynchronous RAID-6 recovery api");
	MODULE_LICENSE("GPL");