Re: [PATCH for-5.3] drm/omap: ensure we have a valid dma_mask

From: Tomi Valkeinen
Date: Fri Aug 09 2019 - 02:40:58 EST


On 08/08/2019 13:10, Christoph Hellwig wrote:
The omapfb platform devices does not have a DMA mask set. The
traditional arm DMA code ignores, but the generic dma-direct/swiotlb
has stricter checks and thus fails mappings without a DMA mask.
As we use swiotlb for arm with LPAE now, omap needs to catch up
and actually set a DMA mask.

Fixes: ad3c7b18c5b3 ("arm: use swiotlb for bounce buffering on LPAE configs")
Reported-by: "H. Nikolaus Schaller" <hns@xxxxxxxxxxxxx>
Tested-by: "H. Nikolaus Schaller" <hns@xxxxxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
drivers/gpu/drm/omapdrm/omap_fbdev.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/omapdrm/omap_fbdev.c b/drivers/gpu/drm/omapdrm/omap_fbdev.c
index 561c4812545b..2c8abf07e617 100644
--- a/drivers/gpu/drm/omapdrm/omap_fbdev.c
+++ b/drivers/gpu/drm/omapdrm/omap_fbdev.c
@@ -232,6 +232,8 @@ void omap_fbdev_init(struct drm_device *dev)
if (!priv->num_pipes)
+ dma_coerce_mask_and_coherent(dev->dev, DMA_BIT_MASK(32));
fbdev = kzalloc(sizeof(*fbdev), GFP_KERNEL);
if (!fbdev)
goto fail;

We do call dma_set_coherent_mask() in omapdrm's probe() (in omap_drv.c), but apparently that's not enough anymore. Changing that call to dma_coerce_mask_and_coherent() removes the WARN. I can create a patch for that, or Christoph can respin this one.

I am not too familiar with the dma mask handling, so maybe someone can educate:

dma_coerce_mask_and_coherent() overwrites dev->dma_mask. Isn't that a bad thing? What if the platform has set dev->dma_mask, and the driver overwrites it with its value? Or who is supposed to set dev->dma_mask?


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