gxp-dmabuf.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Support for using dma-bufs.
 *
 * Copyright (C) 2022 Google LLC
 */

#include <linux/dma-buf.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>
#include <linux/version.h>

#include "gxp-dma.h"
#include "gxp-dmabuf.h"
#include "gxp-vd.h"

struct gxp_dmabuf_mapping {
	struct gxp_mapping mapping;
	struct dma_buf *dmabuf;
	struct dma_buf_attachment *attachment;
	/*
	 * For normal mappings, the `sg_table` is embedded directly in the
	 * `gxp_mapping` and populated by `sg_alloc_table_from_pages()`.
	 * For dma-bufs however, a pointer to the `sg_table` is returned by
	 * `dma_buf_map_attachment()`.
	 *
	 * Rather than manage the memory of `gxp_mapping`'s `sg_table`
	 * independently so it can contain a pointer, dma-bufs store their
	 * `sg_table` pointer here and ignore `mapping->sgt`.
	 */
	struct sg_table *sgt;
};

/* Mapping destructor for gxp_mapping_put() to call */
static void destroy_dmabuf_mapping(struct gxp_mapping *mapping)
{
	struct gxp_dmabuf_mapping *dmabuf_mapping;
	struct gxp_dev *gxp = mapping->gxp;

	/* Unmap and detach the dma-buf */
	dmabuf_mapping =
		container_of(mapping, struct gxp_dmabuf_mapping, mapping);

	gxp_dma_unmap_dmabuf_attachment(gxp, mapping->domain,
					dmabuf_mapping->attachment,
					dmabuf_mapping->sgt, mapping->dir);
	dma_buf_detach(dmabuf_mapping->dmabuf, dmabuf_mapping->attachment);
	dma_buf_put(dmabuf_mapping->dmabuf);

	kfree(dmabuf_mapping);
}

struct gxp_mapping *gxp_dmabuf_map(struct gxp_dev *gxp,
				   struct gcip_iommu_domain *domain, int fd,
				   u32 flags, enum dma_data_direction dir)
{
	struct dma_buf *dmabuf;
	struct dma_buf_attachment *attachment;
	struct sg_table *sgt;
	struct gxp_dmabuf_mapping *dmabuf_mapping;
	int ret = 0;

	if (!valid_dma_direction(dir))
		return ERR_PTR(-EINVAL);

	dmabuf = dma_buf_get(fd);
	if (IS_ERR(dmabuf)) {
		dev_err(gxp->dev, "Failed to get dma-buf to map (ret=%ld)\n",
			PTR_ERR(dmabuf));
		return ERR_CAST(dmabuf);
	}

	attachment = dma_buf_attach(dmabuf, gxp->dev);
	if (IS_ERR(attachment)) {
		dev_err(gxp->dev, "Failed to attach dma-buf to map (ret=%ld)\n",
			PTR_ERR(attachment));
		ret = PTR_ERR(attachment);
		goto err_attach;
	}

	sgt = gxp_dma_map_dmabuf_attachment(gxp, domain, attachment, flags, dir);
	if (IS_ERR(sgt)) {
		dev_err(gxp->dev,
			"Failed to map dma-buf attachment (ret=%ld)\n",
			PTR_ERR(sgt));
		ret = PTR_ERR(sgt);
		goto err_map_attachment;
	}

	dmabuf_mapping = kzalloc(sizeof(*dmabuf_mapping), GFP_KERNEL);
	if (!dmabuf_mapping) {
		ret = -ENOMEM;
		goto err_alloc_mapping;
	}

	/* dma-buf mappings are indicated by a host_address of 0 */
	refcount_set(&dmabuf_mapping->mapping.refcount, 1);
	dmabuf_mapping->mapping.destructor = destroy_dmabuf_mapping;
	dmabuf_mapping->mapping.host_address = 0;
	dmabuf_mapping->mapping.gxp = gxp;
	dmabuf_mapping->mapping.domain = domain;
	dmabuf_mapping->mapping.device_address = sg_dma_address(sgt->sgl);
	dmabuf_mapping->mapping.dir = dir;
	dmabuf_mapping->mapping.size = dmabuf->size;
	dmabuf_mapping->dmabuf = dmabuf;
	dmabuf_mapping->attachment = attachment;
	dmabuf_mapping->sgt = sgt;

	return &dmabuf_mapping->mapping;

err_alloc_mapping:
	gxp_dma_unmap_dmabuf_attachment(gxp, domain, attachment, sgt, dir);
err_map_attachment:
	dma_buf_detach(dmabuf, attachment);
err_attach:
	dma_buf_put(dmabuf);
	return ERR_PTR(ret);
}

struct sg_table *gxp_dmabuf_get_sgt(struct gxp_mapping *mapping)
{
	struct gxp_dmabuf_mapping *dmabuf_mapping;

	if (mapping->host_address)
		/* Not a dmabuf */
		return NULL;

	dmabuf_mapping = container_of(mapping, struct gxp_dmabuf_mapping, mapping);
	return dmabuf_mapping->sgt;
}

#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 16, 0)
MODULE_IMPORT_NS(DMA_BUF);
#endif