Hi Rob,
I run into issues with msm drm driver while implementing a test
application which use v4l2 vidc (venus) decoder driver to decode videos
and msm drm driver to display the decoded frames. The v4l2 test
application use msm drm as dmabuf exporter by DRM_IOCTL_MODE_CREATE_DUMB
and DRM_IOCTL_PRIME_HANDLE_TO_FD from libdrm.
So far the test app is able to decode and display using dmabuf type of
buffers (so, to honest it is slower than using mmap & memcpy but this is
another story). The problems start when destroying drm buffers by call
to DRM_IOCTL_MODE_DESTROY_DUMB ioctl and also when closing dmabuf fd.
The issues I'm seeing are:
- the first and the major one happens in msm_gem_free_object() where we
are trying to free sg table which table is already freed by drm_prime
core in dmabuf .detach callback. In fact the msm_gem_free_object is
called by dmabuf .release callback which should be happened after
.detach. I find weird to call sg_table_free in .detach callback and did
not understand why it is there.
- the second one is again in msm_gem.c::put_pages dma_unmap_sg call.
Some background, vidc (venus) driver use dma-iommu infrastructure copped
from qcom downstream kernel to abstract iommu map/unmap [1].
On the other side when drm driver is exporter it use swiotbl [2] dma map
operations, dma_map_sg will fill sg->dma_address with phy addresses. So
when vidc call dma_map_sg the sg dma_address is filled with iova address
then drm call dma_unmap_sg expecting phy addresses.
If I didn't express myself well, see the hack bellow which I made to
prevent kernel crash.
Any thoughts?
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 7482b06cd08f..c4c0f8084b11 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -155,10 +155,10 @@ static void drm_gem_map_detach(struct dma_buf
*dma_buf,
if (prime_attach->dir != DMA_NONE)
dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents,
prime_attach->dir);
- sg_free_table(sgt);
+/* sg_free_table(sgt);*/
}
- kfree(sgt);
+/* kfree(sgt);*/
kfree(prime_attach);
attach->priv = NULL;
}
diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 9b6220140e99..a78a24ca2fda 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -116,9 +116,10 @@ static void put_pages(struct drm_gem_object *obj)
/* For non-cached buffers, ensure the new pages are clean
* because display controller, GPU, etc. are not coherent:
*/
- if (msm_obj->flags & (MSM_BO_WC|MSM_BO_UNCACHED))
+/* if (msm_obj->flags & (MSM_BO_WC|MSM_BO_UNCACHED))
dma_unmap_sg(obj->dev->dev, msm_obj->sgt->sgl,
msm_obj->sgt->nents,
DMA_BIDIRECTIONAL);
+*/
sg_free_table(msm_obj->sgt);
kfree(msm_obj->sgt);
--
regards,
Stan
[1]
https://git.linaro.org/landing-teams/working/qualcomm/kernel.git/blob/refs/heads/release/qcomlt-4.0:/arch/arm64/mm/dma-mapping.c#l1315
[2]
https://git.linaro.org/landing-teams/working/qualcomm/kernel.git/blob/refs/heads/release/qcomlt-4.0:/arch/arm64/mm/dma-mapping.c#l350
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