[PATCH v9 24/32] drm: host1x: fix common struct sg_table related issues

Marek Szyprowski
2020-08-26T06:37:10Z

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.

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);
--
2.17.1