drivers/gpu/drm/vkms/vkms_composer.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0+

 #include <linux/crc32.h>

 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_blend.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_fixed.h>
 #include <drm/drm_gem_framebuffer_helper.h>
 #include <drm/drm_vblank.h>
 #include <linux/minmax.h>

 #include "vkms_drv.h"

 static u16 pre_mul_blend_channel(u16 src, u16 dst, u16 alpha)
 {
 	u32 new_color;

 	new_color = (src * 0xffff + dst * (0xffff - alpha));

 	return DIV_ROUND_CLOSEST(new_color, 0xffff);
 }

 /**
  * pre_mul_alpha_blend - alpha blending equation
  * @frame_info: Source framebuffer's metadata
  * @stage_buffer: The line with the pixels from src_plane
  * @output_buffer: A line buffer that receives all the blends output
  *
  * Using the information from the `frame_info`, this blends only the
  * necessary pixels from the `stage_buffer` to the `output_buffer`
  * using premultiplied blend formula.
  *
  * The current DRM assumption is that pixel color values have been already
  * pre-multiplied with the alpha channel values. See more
  * drm_plane_create_blend_mode_property(). Also, this formula assumes a
  * completely opaque background.
  */
 static void pre_mul_alpha_blend(struct vkms_frame_info *frame_info,
 				struct line_buffer *stage_buffer,
 				struct line_buffer *output_buffer)
 {
 	int x_dst = frame_info->dst.x1;
 	struct pixel_argb_u16 *out = output_buffer->pixels + x_dst;
 	struct pixel_argb_u16 *in = stage_buffer->pixels;
 	int x_limit = min_t(size_t, drm_rect_width(&frame_info->dst),
 			    stage_buffer->n_pixels);

 	for (int x = 0; x < x_limit; x++) {
 		out[x].a = (u16)0xffff;
 		out[x].r = pre_mul_blend_channel(in[x].r, out[x].r, in[x].a);
 		out[x].g = pre_mul_blend_channel(in[x].g, out[x].g, in[x].a);
 		out[x].b = pre_mul_blend_channel(in[x].b, out[x].b, in[x].a);
 	}
 }

 static int get_y_pos(struct vkms_frame_info *frame_info, int y)
 {
 	if (frame_info->rotation & DRM_MODE_REFLECT_Y)
 		return drm_rect_height(&frame_info->rotated) - y - 1;

 	switch (frame_info->rotation & DRM_MODE_ROTATE_MASK) {
 	case DRM_MODE_ROTATE_90:
 		return frame_info->rotated.x2 - y - 1;
 	case DRM_MODE_ROTATE_270:
 		return y + frame_info->rotated.x1;
 	default:
 		return y;
 	}
 }

 static bool check_limit(struct vkms_frame_info *frame_info, int pos)
 {
 	if (drm_rotation_90_or_270(frame_info->rotation)) {
 		if (pos >= 0 && pos < drm_rect_width(&frame_info->rotated))
 			return true;
 	} else {
 		if (pos >= frame_info->rotated.y1 && pos < frame_info->rotated.y2)
 			return true;
 	}

 	return false;
 }

 static void fill_background(const struct pixel_argb_u16 *background_color,
 			    struct line_buffer *output_buffer)
 {
 	for (size_t i = 0; i < output_buffer->n_pixels; i++)
 		output_buffer->pixels[i] = *background_color;
 }

 // lerp(a, b, t) = a + (b - a) * t
 static u16 lerp_u16(u16 a, u16 b, s64 t)
 {
 	s64 a_fp = drm_int2fixp(a);
 	s64 b_fp = drm_int2fixp(b);

 	s64 delta = drm_fixp_mul(b_fp - a_fp,  t);

 	return drm_fixp2int(a_fp + delta);
 }

 static s64 get_lut_index(const struct vkms_color_lut *lut, u16 channel_value)
 {
 	s64 color_channel_fp = drm_int2fixp(channel_value);

 	return drm_fixp_mul(color_channel_fp, lut->channel_value2index_ratio);
 }

 /*
  * This enum is related to the positions of the variables inside
  * `struct drm_color_lut`, so the order of both needs to be the same.
  */
 enum lut_channel {
 	LUT_RED = 0,
 	LUT_GREEN,
 	LUT_BLUE,
 	LUT_RESERVED
 };

 static u16 apply_lut_to_channel_value(const struct vkms_color_lut *lut, u16 channel_value,
 				      enum lut_channel channel)
 {
 	s64 lut_index = get_lut_index(lut, channel_value);

 	/*
 	 * This checks if `struct drm_color_lut` has any gap added by the compiler
 	 * between the struct fields.
 	 */
 	static_assert(sizeof(struct drm_color_lut) == sizeof(__u16) * 4);

 	u16 *floor_lut_value = (__u16 *)&lut->base[drm_fixp2int(lut_index)];
 	u16 *ceil_lut_value = (__u16 *)&lut->base[drm_fixp2int_ceil(lut_index)];

 	u16 floor_channel_value = floor_lut_value[channel];
 	u16 ceil_channel_value = ceil_lut_value[channel];

 	return lerp_u16(floor_channel_value, ceil_channel_value,
 			lut_index & DRM_FIXED_DECIMAL_MASK);
 }

 static void apply_lut(const struct vkms_crtc_state *crtc_state, struct line_buffer *output_buffer)
 {
 	if (!crtc_state->gamma_lut.base)
 		return;

 	if (!crtc_state->gamma_lut.lut_length)
 		return;

 	for (size_t x = 0; x < output_buffer->n_pixels; x++) {
 		struct pixel_argb_u16 *pixel = &output_buffer->pixels[x];

 		pixel->r = apply_lut_to_channel_value(&crtc_state->gamma_lut, pixel->r, LUT_RED);
 		pixel->g = apply_lut_to_channel_value(&crtc_state->gamma_lut, pixel->g, LUT_GREEN);
 		pixel->b = apply_lut_to_channel_value(&crtc_state->gamma_lut, pixel->b, LUT_BLUE);
 	}
 }

 /**
  * blend - blend the pixels from all planes and compute crc
  * @wb: The writeback frame buffer metadata
  * @crtc_state: The crtc state
  * @crc32: The crc output of the final frame
  * @output_buffer: A buffer of a row that will receive the result of the blend(s)
  * @stage_buffer: The line with the pixels from plane being blend to the output
  * @row_size: The size, in bytes, of a single row
  *
  * This function blends the pixels (Using the `pre_mul_alpha_blend`)
  * from all planes, calculates the crc32 of the output from the former step,
  * and, if necessary, convert and store the output to the writeback buffer.
  */
 static void blend(struct vkms_writeback_job *wb,
 		  struct vkms_crtc_state *crtc_state,
 		  u32 *crc32, struct line_buffer *stage_buffer,
 		  struct line_buffer *output_buffer, size_t row_size)
 {
 	struct vkms_plane_state **plane = crtc_state->active_planes;
 	u32 n_active_planes = crtc_state->num_active_planes;
 	int y_pos;

 	const struct pixel_argb_u16 background_color = { .a = 0xffff };

 	size_t crtc_y_limit = crtc_state->base.crtc->mode.vdisplay;

 	for (size_t y = 0; y < crtc_y_limit; y++) {
 		fill_background(&background_color, output_buffer);

 		/* The active planes are composed associatively in z-order. */
 		for (size_t i = 0; i < n_active_planes; i++) {
 			y_pos = get_y_pos(plane[i]->frame_info, y);

 			if (!check_limit(plane[i]->frame_info, y_pos))
 				continue;

 			vkms_compose_row(stage_buffer, plane[i], y_pos);
 			pre_mul_alpha_blend(plane[i]->frame_info, stage_buffer,
 					    output_buffer);
 		}

 		apply_lut(crtc_state, output_buffer);

 		*crc32 = crc32_le(*crc32, (void *)output_buffer->pixels, row_size);

 		if (wb)
 			vkms_writeback_row(wb, output_buffer, y_pos);
 	}
 }

 static int check_format_funcs(struct vkms_crtc_state *crtc_state,
 			      struct vkms_writeback_job *active_wb)
 {
 	struct vkms_plane_state **planes = crtc_state->active_planes;
 	u32 n_active_planes = crtc_state->num_active_planes;

 	for (size_t i = 0; i < n_active_planes; i++)
 		if (!planes[i]->pixel_read)
 			return -1;

 	if (active_wb && !active_wb->pixel_write)
 		return -1;

 	return 0;
 }

 static int check_iosys_map(struct vkms_crtc_state *crtc_state)
 {
 	struct vkms_plane_state **plane_state = crtc_state->active_planes;
 	u32 n_active_planes = crtc_state->num_active_planes;

 	for (size_t i = 0; i < n_active_planes; i++)
 		if (iosys_map_is_null(&plane_state[i]->frame_info->map[0]))
 			return -1;

 	return 0;
 }

 static int compose_active_planes(struct vkms_writeback_job *active_wb,
 				 struct vkms_crtc_state *crtc_state,
 				 u32 *crc32)
 {
 	size_t line_width, pixel_size = sizeof(struct pixel_argb_u16);
 	struct line_buffer output_buffer, stage_buffer;
 	int ret = 0;

 	/*
 	 * This check exists so we can call `crc32_le` for the entire line
 	 * instead doing it for each channel of each pixel in case
 	 * `struct `pixel_argb_u16` had any gap added by the compiler
 	 * between the struct fields.
 	 */
 	static_assert(sizeof(struct pixel_argb_u16) == 8);

 	if (WARN_ON(check_iosys_map(crtc_state)))
 		return -EINVAL;

 	if (WARN_ON(check_format_funcs(crtc_state, active_wb)))
 		return -EINVAL;

 	line_width = crtc_state->base.crtc->mode.hdisplay;
 	stage_buffer.n_pixels = line_width;
 	output_buffer.n_pixels = line_width;

 	stage_buffer.pixels = kvmalloc(line_width * pixel_size, GFP_KERNEL);
 	if (!stage_buffer.pixels) {
 		DRM_ERROR("Cannot allocate memory for the output line buffer");
 		return -ENOMEM;
 	}

 	output_buffer.pixels = kvmalloc(line_width * pixel_size, GFP_KERNEL);
 	if (!output_buffer.pixels) {
 		DRM_ERROR("Cannot allocate memory for intermediate line buffer");
 		ret = -ENOMEM;
 		goto free_stage_buffer;
 	}

 	blend(active_wb, crtc_state, crc32, &stage_buffer,
 	      &output_buffer, line_width * pixel_size);

 	kvfree(output_buffer.pixels);
 free_stage_buffer:
 	kvfree(stage_buffer.pixels);

 	return ret;
 }

 /**
  * vkms_composer_worker - ordered work_struct to compute CRC
  *
  * @work: work_struct
  *
  * Work handler for composing and computing CRCs. work_struct scheduled in
  * an ordered workqueue that's periodically scheduled to run by
  * vkms_vblank_simulate() and flushed at vkms_atomic_commit_tail().
  */
 void vkms_composer_worker(struct work_struct *work)
 {
 	struct vkms_crtc_state *crtc_state = container_of(work,
 						struct vkms_crtc_state,
 						composer_work);
 	struct drm_crtc *crtc = crtc_state->base.crtc;
 	struct vkms_writeback_job *active_wb = crtc_state->active_writeback;
 	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
 	bool crc_pending, wb_pending;
 	u64 frame_start, frame_end;
 	u32 crc32 = 0;
 	int ret;

 	spin_lock_irq(&out->composer_lock);
 	frame_start = crtc_state->frame_start;
 	frame_end = crtc_state->frame_end;
 	crc_pending = crtc_state->crc_pending;
 	wb_pending = crtc_state->wb_pending;
 	crtc_state->frame_start = 0;
 	crtc_state->frame_end = 0;
 	crtc_state->crc_pending = false;

 	if (crtc->state->gamma_lut) {
 		s64 max_lut_index_fp;
 		s64 u16_max_fp = drm_int2fixp(0xffff);

 		crtc_state->gamma_lut.base = (struct drm_color_lut *)crtc->state->gamma_lut->data;
 		crtc_state->gamma_lut.lut_length =
 			crtc->state->gamma_lut->length / sizeof(struct drm_color_lut);
 		max_lut_index_fp = drm_int2fixp(crtc_state->gamma_lut.lut_length  - 1);
 		crtc_state->gamma_lut.channel_value2index_ratio = drm_fixp_div(max_lut_index_fp,
 									       u16_max_fp);

 	} else {
 		crtc_state->gamma_lut.base = NULL;
 	}

 	spin_unlock_irq(&out->composer_lock);

 	/*
 	 * We raced with the vblank hrtimer and previous work already computed
 	 * the crc, nothing to do.
 	 */
 	if (!crc_pending)
 		return;

 	if (wb_pending)
 		ret = compose_active_planes(active_wb, crtc_state, &crc32);
 	else
 		ret = compose_active_planes(NULL, crtc_state, &crc32);

 	if (ret)
 		return;

 	if (wb_pending) {
 		drm_writeback_signal_completion(&out->wb_connector, 0);
 		spin_lock_irq(&out->composer_lock);
 		crtc_state->wb_pending = false;
 		spin_unlock_irq(&out->composer_lock);
 	}

 	/*
 	 * The worker can fall behind the vblank hrtimer, make sure we catch up.
 	 */
 	while (frame_start <= frame_end)
 		drm_crtc_add_crc_entry(crtc, true, frame_start++, &crc32);
 }

 static const char * const pipe_crc_sources[] = {"auto"};

 const char *const *vkms_get_crc_sources(struct drm_crtc *crtc,
 					size_t *count)
 {
 	*count = ARRAY_SIZE(pipe_crc_sources);
 	return pipe_crc_sources;
 }

 static int vkms_crc_parse_source(const char *src_name, bool *enabled)
 {
 	int ret = 0;

 	if (!src_name) {
 		*enabled = false;
 	} else if (strcmp(src_name, "auto") == 0) {
 		*enabled = true;
 	} else {
 		*enabled = false;
 		ret = -EINVAL;
 	}

 	return ret;
 }

 int vkms_verify_crc_source(struct drm_crtc *crtc, const char *src_name,
 			   size_t *values_cnt)
 {
 	bool enabled;

 	if (vkms_crc_parse_source(src_name, &enabled) < 0) {
 		DRM_DEBUG_DRIVER("unknown source %s\n", src_name);
 		return -EINVAL;
 	}

 	*values_cnt = 1;

 	return 0;
 }

 void vkms_set_composer(struct vkms_output *out, bool enabled)
 {
 	bool old_enabled;

 	if (enabled)
 		drm_crtc_vblank_get(&out->crtc);

 	spin_lock_irq(&out->lock);
 	old_enabled = out->composer_enabled;
 	out->composer_enabled = enabled;
 	spin_unlock_irq(&out->lock);

 	if (old_enabled)
 		drm_crtc_vblank_put(&out->crtc);
 }

 int vkms_set_crc_source(struct drm_crtc *crtc, const char *src_name)
 {
 	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
 	bool enabled = false;
 	int ret = 0;

 	ret = vkms_crc_parse_source(src_name, &enabled);

 	vkms_set_composer(out, enabled);

 	return ret;
 }
	// SPDX-License-Identifier: GPL-2.0+

	#include <linux/crc32.h>

	#include <drm/drm_atomic.h>
	#include <drm/drm_atomic_helper.h>
	#include <drm/drm_blend.h>
	#include <drm/drm_fourcc.h>
	#include <drm/drm_fixed.h>
	#include <drm/drm_gem_framebuffer_helper.h>
	#include <drm/drm_vblank.h>
	#include <linux/minmax.h>

	#include "vkms_drv.h"

	static u16 pre_mul_blend_channel(u16 src, u16 dst, u16 alpha)
	{
	u32 new_color;

	new_color = (src * 0xffff + dst * (0xffff - alpha));

	return DIV_ROUND_CLOSEST(new_color, 0xffff);
	}

	/**
	* pre_mul_alpha_blend - alpha blending equation
	* @frame_info: Source framebuffer's metadata
	* @stage_buffer: The line with the pixels from src_plane
	* @output_buffer: A line buffer that receives all the blends output
	*
	* Using the information from the `frame_info`, this blends only the
	* necessary pixels from the `stage_buffer` to the `output_buffer`
	* using premultiplied blend formula.
	*
	* The current DRM assumption is that pixel color values have been already
	* pre-multiplied with the alpha channel values. See more
	* drm_plane_create_blend_mode_property(). Also, this formula assumes a
	* completely opaque background.
	*/
	static void pre_mul_alpha_blend(struct vkms_frame_info *frame_info,
	struct line_buffer *stage_buffer,
	struct line_buffer *output_buffer)
	{
	int x_dst = frame_info->dst.x1;
	struct pixel_argb_u16 *out = output_buffer->pixels + x_dst;
	struct pixel_argb_u16 *in = stage_buffer->pixels;
	int x_limit = min_t(size_t, drm_rect_width(&frame_info->dst),
	stage_buffer->n_pixels);

	for (int x = 0; x < x_limit; x++) {
	out[x].a = (u16)0xffff;
	out[x].r = pre_mul_blend_channel(in[x].r, out[x].r, in[x].a);
	out[x].g = pre_mul_blend_channel(in[x].g, out[x].g, in[x].a);
	out[x].b = pre_mul_blend_channel(in[x].b, out[x].b, in[x].a);
	}
	}

	static int get_y_pos(struct vkms_frame_info *frame_info, int y)
	{
	if (frame_info->rotation & DRM_MODE_REFLECT_Y)
	return drm_rect_height(&frame_info->rotated) - y - 1;

	switch (frame_info->rotation & DRM_MODE_ROTATE_MASK) {
	case DRM_MODE_ROTATE_90:
	return frame_info->rotated.x2 - y - 1;
	case DRM_MODE_ROTATE_270:
	return y + frame_info->rotated.x1;
	default:
	return y;
	}
	}

	static bool check_limit(struct vkms_frame_info *frame_info, int pos)
	{
	if (drm_rotation_90_or_270(frame_info->rotation)) {
	if (pos >= 0 && pos < drm_rect_width(&frame_info->rotated))
	return true;
	} else {
	if (pos >= frame_info->rotated.y1 && pos < frame_info->rotated.y2)
	return true;
	}

	return false;
	}

	static void fill_background(const struct pixel_argb_u16 *background_color,
	struct line_buffer *output_buffer)
	{
	for (size_t i = 0; i < output_buffer->n_pixels; i++)
	output_buffer->pixels[i] = *background_color;
	}

	// lerp(a, b, t) = a + (b - a) * t
	static u16 lerp_u16(u16 a, u16 b, s64 t)
	{
	s64 a_fp = drm_int2fixp(a);
	s64 b_fp = drm_int2fixp(b);

	s64 delta = drm_fixp_mul(b_fp - a_fp, t);

	return drm_fixp2int(a_fp + delta);
	}

	static s64 get_lut_index(const struct vkms_color_lut *lut, u16 channel_value)
	{
	s64 color_channel_fp = drm_int2fixp(channel_value);

	return drm_fixp_mul(color_channel_fp, lut->channel_value2index_ratio);
	}

	/*
	* This enum is related to the positions of the variables inside
	* `struct drm_color_lut`, so the order of both needs to be the same.
	*/
	enum lut_channel {
	LUT_RED = 0,
	LUT_GREEN,
	LUT_BLUE,
	LUT_RESERVED
	};

	static u16 apply_lut_to_channel_value(const struct vkms_color_lut *lut, u16 channel_value,
	enum lut_channel channel)
	{
	s64 lut_index = get_lut_index(lut, channel_value);

	/*
	* This checks if `struct drm_color_lut` has any gap added by the compiler
	* between the struct fields.
	*/
	static_assert(sizeof(struct drm_color_lut) == sizeof(__u16) * 4);

	u16 floor_lut_value = (__u16 )&lut->base[drm_fixp2int(lut_index)];
	u16 ceil_lut_value = (__u16 )&lut->base[drm_fixp2int_ceil(lut_index)];

	u16 floor_channel_value = floor_lut_value[channel];
	u16 ceil_channel_value = ceil_lut_value[channel];

	return lerp_u16(floor_channel_value, ceil_channel_value,
	lut_index & DRM_FIXED_DECIMAL_MASK);
	}

	static void apply_lut(const struct vkms_crtc_state crtc_state, struct line_buffer output_buffer)
	{
	if (!crtc_state->gamma_lut.base)
	return;

	if (!crtc_state->gamma_lut.lut_length)
	return;

	for (size_t x = 0; x < output_buffer->n_pixels; x++) {
	struct pixel_argb_u16 *pixel = &output_buffer->pixels[x];

	pixel->r = apply_lut_to_channel_value(&crtc_state->gamma_lut, pixel->r, LUT_RED);
	pixel->g = apply_lut_to_channel_value(&crtc_state->gamma_lut, pixel->g, LUT_GREEN);
	pixel->b = apply_lut_to_channel_value(&crtc_state->gamma_lut, pixel->b, LUT_BLUE);
	}
	}

	/**
	* blend - blend the pixels from all planes and compute crc
	* @wb: The writeback frame buffer metadata
	* @crtc_state: The crtc state
	* @crc32: The crc output of the final frame
	* @output_buffer: A buffer of a row that will receive the result of the blend(s)
	* @stage_buffer: The line with the pixels from plane being blend to the output
	* @row_size: The size, in bytes, of a single row
	*
	* This function blends the pixels (Using the `pre_mul_alpha_blend`)
	* from all planes, calculates the crc32 of the output from the former step,
	* and, if necessary, convert and store the output to the writeback buffer.
	*/
	static void blend(struct vkms_writeback_job *wb,
	struct vkms_crtc_state *crtc_state,
	u32 crc32, struct line_buffer stage_buffer,
	struct line_buffer *output_buffer, size_t row_size)
	{
	struct vkms_plane_state **plane = crtc_state->active_planes;
	u32 n_active_planes = crtc_state->num_active_planes;
	int y_pos;

	const struct pixel_argb_u16 background_color = { .a = 0xffff };

	size_t crtc_y_limit = crtc_state->base.crtc->mode.vdisplay;

	for (size_t y = 0; y < crtc_y_limit; y++) {
	fill_background(&background_color, output_buffer);

	/* The active planes are composed associatively in z-order. */
	for (size_t i = 0; i < n_active_planes; i++) {
	y_pos = get_y_pos(plane[i]->frame_info, y);

	if (!check_limit(plane[i]->frame_info, y_pos))
	continue;

	vkms_compose_row(stage_buffer, plane[i], y_pos);
	pre_mul_alpha_blend(plane[i]->frame_info, stage_buffer,
	output_buffer);
	}

	apply_lut(crtc_state, output_buffer);

	crc32 = crc32_le(crc32, (void *)output_buffer->pixels, row_size);

	if (wb)
	vkms_writeback_row(wb, output_buffer, y_pos);
	}
	}

	static int check_format_funcs(struct vkms_crtc_state *crtc_state,
	struct vkms_writeback_job *active_wb)
	{
	struct vkms_plane_state **planes = crtc_state->active_planes;
	u32 n_active_planes = crtc_state->num_active_planes;

	for (size_t i = 0; i < n_active_planes; i++)
	if (!planes[i]->pixel_read)
	return -1;

	if (active_wb && !active_wb->pixel_write)
	return -1;

	return 0;
	}

	static int check_iosys_map(struct vkms_crtc_state *crtc_state)
	{
	struct vkms_plane_state **plane_state = crtc_state->active_planes;
	u32 n_active_planes = crtc_state->num_active_planes;

	for (size_t i = 0; i < n_active_planes; i++)
	if (iosys_map_is_null(&plane_state[i]->frame_info->map[0]))
	return -1;

	return 0;
	}

	static int compose_active_planes(struct vkms_writeback_job *active_wb,
	struct vkms_crtc_state *crtc_state,
	u32 *crc32)
	{
	size_t line_width, pixel_size = sizeof(struct pixel_argb_u16);
	struct line_buffer output_buffer, stage_buffer;
	int ret = 0;

	/*
	* This check exists so we can call `crc32_le` for the entire line
	* instead doing it for each channel of each pixel in case
	* `struct `pixel_argb_u16` had any gap added by the compiler
	* between the struct fields.
	*/
	static_assert(sizeof(struct pixel_argb_u16) == 8);

	if (WARN_ON(check_iosys_map(crtc_state)))
	return -EINVAL;

	if (WARN_ON(check_format_funcs(crtc_state, active_wb)))
	return -EINVAL;

	line_width = crtc_state->base.crtc->mode.hdisplay;
	stage_buffer.n_pixels = line_width;
	output_buffer.n_pixels = line_width;

	stage_buffer.pixels = kvmalloc(line_width * pixel_size, GFP_KERNEL);
	if (!stage_buffer.pixels) {
	DRM_ERROR("Cannot allocate memory for the output line buffer");
	return -ENOMEM;
	}

	output_buffer.pixels = kvmalloc(line_width * pixel_size, GFP_KERNEL);
	if (!output_buffer.pixels) {
	DRM_ERROR("Cannot allocate memory for intermediate line buffer");
	ret = -ENOMEM;
	goto free_stage_buffer;
	}

	blend(active_wb, crtc_state, crc32, &stage_buffer,
	&output_buffer, line_width * pixel_size);

	kvfree(output_buffer.pixels);
	free_stage_buffer:
	kvfree(stage_buffer.pixels);

	return ret;
	}

	/**
	* vkms_composer_worker - ordered work_struct to compute CRC
	*
	* @work: work_struct
	*
	* Work handler for composing and computing CRCs. work_struct scheduled in
	* an ordered workqueue that's periodically scheduled to run by
	* vkms_vblank_simulate() and flushed at vkms_atomic_commit_tail().
	*/
	void vkms_composer_worker(struct work_struct *work)
	{
	struct vkms_crtc_state *crtc_state = container_of(work,
	struct vkms_crtc_state,
	composer_work);
	struct drm_crtc *crtc = crtc_state->base.crtc;
	struct vkms_writeback_job *active_wb = crtc_state->active_writeback;
	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
	bool crc_pending, wb_pending;
	u64 frame_start, frame_end;
	u32 crc32 = 0;
	int ret;

	spin_lock_irq(&out->composer_lock);
	frame_start = crtc_state->frame_start;
	frame_end = crtc_state->frame_end;
	crc_pending = crtc_state->crc_pending;
	wb_pending = crtc_state->wb_pending;
	crtc_state->frame_start = 0;
	crtc_state->frame_end = 0;
	crtc_state->crc_pending = false;

	if (crtc->state->gamma_lut) {
	s64 max_lut_index_fp;
	s64 u16_max_fp = drm_int2fixp(0xffff);

	crtc_state->gamma_lut.base = (struct drm_color_lut *)crtc->state->gamma_lut->data;
	crtc_state->gamma_lut.lut_length =
	crtc->state->gamma_lut->length / sizeof(struct drm_color_lut);
	max_lut_index_fp = drm_int2fixp(crtc_state->gamma_lut.lut_length - 1);
	crtc_state->gamma_lut.channel_value2index_ratio = drm_fixp_div(max_lut_index_fp,
	u16_max_fp);

	} else {
	crtc_state->gamma_lut.base = NULL;
	}

	spin_unlock_irq(&out->composer_lock);

	/*
	* We raced with the vblank hrtimer and previous work already computed
	* the crc, nothing to do.
	*/
	if (!crc_pending)
	return;

	if (wb_pending)
	ret = compose_active_planes(active_wb, crtc_state, &crc32);
	else
	ret = compose_active_planes(NULL, crtc_state, &crc32);

	if (ret)
	return;

	if (wb_pending) {
	drm_writeback_signal_completion(&out->wb_connector, 0);
	spin_lock_irq(&out->composer_lock);
	crtc_state->wb_pending = false;
	spin_unlock_irq(&out->composer_lock);
	}

	/*
	* The worker can fall behind the vblank hrtimer, make sure we catch up.
	*/
	while (frame_start <= frame_end)
	drm_crtc_add_crc_entry(crtc, true, frame_start++, &crc32);
	}

	static const char * const pipe_crc_sources[] = {"auto"};

	const char const vkms_get_crc_sources(struct drm_crtc *crtc,
	size_t *count)
	{
	*count = ARRAY_SIZE(pipe_crc_sources);
	return pipe_crc_sources;
	}

	static int vkms_crc_parse_source(const char src_name, bool enabled)
	{
	int ret = 0;

	if (!src_name) {
	*enabled = false;
	} else if (strcmp(src_name, "auto") == 0) {
	*enabled = true;
	} else {
	*enabled = false;
	ret = -EINVAL;
	}

	return ret;
	}

	int vkms_verify_crc_source(struct drm_crtc crtc, const char src_name,
	size_t *values_cnt)
	{
	bool enabled;

	if (vkms_crc_parse_source(src_name, &enabled) < 0) {
	DRM_DEBUG_DRIVER("unknown source %s\n", src_name);
	return -EINVAL;
	}

	*values_cnt = 1;

	return 0;
	}

	void vkms_set_composer(struct vkms_output *out, bool enabled)
	{
	bool old_enabled;

	if (enabled)
	drm_crtc_vblank_get(&out->crtc);

	spin_lock_irq(&out->lock);
	old_enabled = out->composer_enabled;
	out->composer_enabled = enabled;
	spin_unlock_irq(&out->lock);

	if (old_enabled)
	drm_crtc_vblank_put(&out->crtc);
	}

	int vkms_set_crc_source(struct drm_crtc crtc, const char src_name)
	{
	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
	bool enabled = false;
	int ret = 0;

	ret = vkms_crc_parse_source(src_name, &enabled);

	vkms_set_composer(out, enabled);

	return ret;
	}