[PATCH] drm/exynos: Add check for dma_set_max_seg_size

[PATCH] drm/exynos: Add check for dma_set_max_seg_size

[Chen Ni]

Add check for the return value of dma_set_max_seg_size() and return
the error if it fails in order to catch the error.

Fixes: ddfd4ab6bb08 ("drm/exynos: Fix dma_parms allocation")
Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
---
 drivers/gpu/drm/exynos/exynos_drm_dma.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_dma.c b/drivers/gpu/drm/exynos/exynos_drm_dma.c
index e2c7373f20c6..0f942186f3ff 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_dma.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_dma.c
@@ -51,7 +51,10 @@ static int drm_iommu_attach_device(struct drm_device *drm_dev,
 		return -EINVAL;
 	}
 
-	dma_set_max_seg_size(subdrv_dev, DMA_BIT_MASK(32));
+	ret = dma_set_max_seg_size(subdrv_dev, DMA_BIT_MASK(32));
+	if (ret)
+		return ret;
+
 	if (IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU)) {
 		/*
 		 * Keep the original DMA mapping of the sub-device and
-- 
2.25.1


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Re: [PATCH] drm/exynos: Add check for dma_set_max_seg_size

[Christoph Hellwig]

On Mon, Apr 29, 2024 at 10:38:33AM +0800, Chen Ni wrote:
> Add check for the return value of dma_set_max_seg_size() and return
> the error if it fails in order to catch the error.
> 
> Fixes: ddfd4ab6bb08 ("drm/exynos: Fix dma_parms allocation")
> Signed-off-by: Chen Ni <nichen@iscas.ac.cn>

With my dma-mapping hat maintainer on I think we should remove the
return value from it.  It can only return -EIO or 0, and the first
only if the bus has not set up a dma_params structure for the device.
I'd much rather WARN_ON() on that, as it is is a grave error to either
call dma_set_max_seg_size on a device that is on a bus that doesn't
support DMA at all, or for the bus maintainer to accidentlaly drop it.

Feel free to add the patch if exynos has a strict error checking policy,
but it's rather pointless and I'll add removing the return value to my
ever growing TODO list.


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