[PATCH v10 00/17] drm/exynos: atomic modesetting support

[Marek Szyprowski]

Hello,

On 2015-06-01 17:04, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan at collabora.co.uk>
>
> Hi,
>
> Here goes the full support for atomic modesetting on exynos. I've
> split the patches in the various phases of atomic support.

Thanks for this patchses, however I've noticed a problem after applying 
them.
The issue gets revealed when support for IOMMU is enabled. I've did my tests
with Exynos HDMI driver on Odroid U3 board.

To demonstrated the issue I've added following additional debug in the 
exynos
mixer driver in mixer_graph_buffer() function:
pr_info("dma addr %pad plane->src_width %d plane->src_height %d\n", 
&plane->dma_addr[0], plane->src_width, plane->src_height);

Before applying patches setting 640x480 mode and getting back to 1920x1080
console generates following log:

# modetest -M exynos -s 23:640x480
setting mode 640x480-60Hz at XR24 on connectors 23, crtc 21
[ 3860.617151] dma 0xbc500000 plane->src_width 640 plane->src_height 480
^C
[ 3870.555232] dma 0xbbd00000 plane->src_width 1920 plane->src_height 1080
[ 3870.565696] dma 0xbbd00000 plane->src_width 1920 plane->src_height 1080

After applying atomic modesetting patchset:
# modetest -M exynos -s 24:640x480
[  142.540122] dma 0xbbd00000 plane->src_width 1920 plane->src_height 1080
[  142.550726] dma 0xbbd00000 plane->src_width 1920 plane->src_height 1080
setting mode 640x480-60Hz at XR24 on connectors 24, crtc 22
[  142.643672] dma 0xbc500000 plane->src_width 1920 plane->src_height 1080
[  142.759982] dma 0xbc500000 plane->src_width 640 plane->src_height 480
^C
[  154.986040] dma 0xbbd00000 plane->src_width 1920 plane->src_height 1080

As you can see from the above log, mixer_graph_buffer function is called
several times. 0xbbd00000 is the DMA address of the 1920x1080 framebuffer
and 0xbc500000 is the DMA address of the allocated 640x480 buffer.
mixer_graph_buffer() is first called with the new DMA address of the
framebuffer, but with the old mode parameters (1920x1080 size) and then
in the next call it updates the plane parameters to the correct values
(size changed to 640x480). When IOMMU is not used, this can be easily
missed, but after enabling IOMMU support, any DMA access to unallocated
address causes IOMMU PAGE FAULT. Here it will happen after changing DMA
address of the buffer without changing the size.

A quick workaround to resolve this multiple calls to mixer_graph_buffer()
with partially updated mode values is to remove calls to
mixer_window_suspend/mixer_window_resume from mixer_disable and
mixer_disable functions, but I expect that this is not the right
approach.

Probably the same problem can be observed with Exynos FIMD driver.

Gustavo: could you check if mixer_enable functions should really
call mixer_window_resume function, which in turn calls mixer_win_commit,
which calls mixer_graph_buffer with partially updated display buffer
data?

 > (...)

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland