drivers/gpu/drm/amd/amdgpu/amdgpu_wb.c

// SPDX-License-Identifier: GPL-2.0 OR MIT
/*
 * Copyright 2026 Advanced Micro Devices, Inc.

 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */
#include <linux/spinlock.h>

#include "amdgpu.h"
#include "amdgpu_wb.h"

/*
 * amdgpu_wb_*()
 * Writeback is the method by which the GPU updates special pages in memory
 * with the status of certain GPU events (fences, ring pointers,etc.).
 */

/**
 * amdgpu_wb_fini - Disable Writeback and free memory
 *
 * @adev: amdgpu_device pointer
 *
 * Disables Writeback and frees the Writeback memory (all asics).
 * Used at driver shutdown.
 */
void amdgpu_wb_fini(struct amdgpu_device *adev)
{
	if (adev->wb.wb_obj) {
		amdgpu_bo_free_kernel(&adev->wb.wb_obj,
				      &adev->wb.gpu_addr,
				      (void **)&adev->wb.wb);
		adev->wb.wb_obj = NULL;
	}
}

/**
 * amdgpu_wb_init - Init Writeback driver info and allocate memory
 *
 * @adev: amdgpu_device pointer
 *
 * Initializes writeback and allocates writeback memory (all asics).
 * Used at driver startup.
 * Returns 0 on success or an -error on failure.
 */
int amdgpu_wb_init(struct amdgpu_device *adev)
{
	int r;

	if (adev->wb.wb_obj == NULL) {
		/* AMDGPU_MAX_WB * sizeof(uint32_t) * 8 = AMDGPU_MAX_WB 256bit slots */
		r = amdgpu_bo_create_kernel(adev, AMDGPU_MAX_WB * sizeof(uint32_t) * 8,
					    PAGE_SIZE, AMDGPU_GEM_DOMAIN_GTT,
					    &adev->wb.wb_obj, &adev->wb.gpu_addr,
					    (void **)&adev->wb.wb);
		if (r) {
			dev_warn(adev->dev, "(%d) create WB bo failed\n", r);
			return r;
		}

		adev->wb.num_wb = AMDGPU_MAX_WB;
		memset(&adev->wb.used, 0, sizeof(adev->wb.used));

		/* clear wb memory */
		memset((char *)adev->wb.wb, 0, AMDGPU_MAX_WB * sizeof(uint32_t) * 8);
	}

	return 0;
}

/**
 * amdgpu_wb_get - Allocate a wb entry
 *
 * @adev: amdgpu_device pointer
 * @wb: wb index
 *
 * Allocate a wb slot for use by the driver (all asics).
 * Returns 0 on success or -EINVAL on failure.
 */
int amdgpu_wb_get(struct amdgpu_device *adev, u32 *wb)
{
	unsigned long flags, offset;

	spin_lock_irqsave(&adev->wb.lock, flags);
	offset = find_first_zero_bit(adev->wb.used, adev->wb.num_wb);
	if (offset < adev->wb.num_wb) {
		__set_bit(offset, adev->wb.used);
		spin_unlock_irqrestore(&adev->wb.lock, flags);
		*wb = offset << 3; /* convert to dw offset */
		return 0;
	} else {
		spin_unlock_irqrestore(&adev->wb.lock, flags);
		return -EINVAL;
	}
}

/**
 * amdgpu_wb_free - Free a wb entry
 *
 * @adev: amdgpu_device pointer
 * @wb: wb index
 *
 * Free a wb slot allocated for use by the driver (all asics)
 */
void amdgpu_wb_free(struct amdgpu_device *adev, u32 wb)
{
	unsigned long flags;

	wb >>= 3;
	spin_lock_irqsave(&adev->wb.lock, flags);
	if (wb < adev->wb.num_wb)
		__clear_bit(wb, adev->wb.used);
	spin_unlock_irqrestore(&adev->wb.lock, flags);
}