On 2020-08-26 07:33, Marek Szyprowski wrote:
The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function returns the number of the created entries in the DMA address space. However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and dma_unmap_sg must be called with the original number of the entries passed to the dma_map_sg().
struct sg_table is a common structure used for describing a non-contiguous memory buffer, used commonly in the DRM and graphics subsystems. It consists of a scatterlist with memory pages and DMA addresses (sgl entry), as well as the number of scatterlist entries: CPU pages (orig_nents entry) and DMA mapped pages (nents entry).
It turned out that it was a common mistake to misuse nents and orig_nents entries, calling DMA-mapping functions with a wrong number of entries or ignoring the number of mapped entries returned by the dma_map_sg() function.
To avoid such issues, lets use a common dma-mapping wrappers operating directly on the struct sg_table objects and use scatterlist page iterators where possible. This, almost always, hides references to the nents and orig_nents entries, making the code robust, easier to follow and copy/paste safe.
Reviewed-by: Robin Murphy robin.murphy@arm.com
Signed-off-by: Marek Szyprowski m.szyprowski@samsung.com
drivers/gpu/host1x/job.c | 22 ++++++++-------------- 1 file changed, 8 insertions(+), 14 deletions(-)
diff --git a/drivers/gpu/host1x/job.c b/drivers/gpu/host1x/job.c index 89b6c14b7392..82d0a60ba3f7 100644 --- a/drivers/gpu/host1x/job.c +++ b/drivers/gpu/host1x/job.c @@ -170,11 +170,9 @@ static unsigned int pin_job(struct host1x *host, struct host1x_job *job) goto unpin; }
err = dma_map_sg(dev, sgt->sgl, sgt->nents, dir);if (!err) {err = -ENOMEM;
err = dma_map_sgtable(dev, sgt, dir, 0);if (err) goto unpin;
}job->unpins[job->num_unpins].dev = dev; job->unpins[job->num_unpins].dir = dir; @@ -228,7 +226,7 @@ static unsigned int pin_job(struct host1x *host, struct host1x_job *job) } if (host->domain) {
for_each_sg(sgt->sgl, sg, sgt->nents, j)
for_each_sgtable_sg(sgt, sg, j) gather_size += sg->length; gather_size = iova_align(&host->iova, gather_size);@@ -240,9 +238,9 @@ static unsigned int pin_job(struct host1x *host, struct host1x_job *job) goto put; }
err = iommu_map_sg(host->domain,
err = iommu_map_sgtable(host->domain, iova_dma_addr(&host->iova, alloc),
sgt->sgl, sgt->nents, IOMMU_READ);
sgt, IOMMU_READ); if (err == 0) { __free_iova(&host->iova, alloc); err = -EINVAL;@@ -252,12 +250,9 @@ static unsigned int pin_job(struct host1x *host, struct host1x_job *job) job->unpins[job->num_unpins].size = gather_size; phys_addr = iova_dma_addr(&host->iova, alloc); } else if (sgt) {
err = dma_map_sg(host->dev, sgt->sgl, sgt->nents,DMA_TO_DEVICE);if (!err) {err = -ENOMEM;
err = dma_map_sgtable(host->dev, sgt, DMA_TO_DEVICE, 0);if (err) goto put;
}job->unpins[job->num_unpins].dir = DMA_TO_DEVICE; job->unpins[job->num_unpins].dev = host->dev; @@ -660,8 +655,7 @@ void host1x_job_unpin(struct host1x_job *job) } if (unpin->dev && sgt)
dma_unmap_sg(unpin->dev, sgt->sgl, sgt->nents,unpin->dir);
dma_unmap_sgtable(unpin->dev, sgt, unpin->dir, 0);host1x_bo_unpin(dev, unpin->bo, sgt); host1x_bo_put(unpin->bo);