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

[Gustavo Padovan <gustavo.padovan@collabora.co.uk>]

Hi Marek,

2015-06-10 Marek Szyprowski <m.szyprowski@samsung.com>:

> Hello,
> 
> On 2015-06-01 17:04, Gustavo Padovan wrote:
> >From: Gustavo Padovan <gustavo.padovan@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@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@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?

It should not, you are right. This is actually the correct fix. Atomic
modesetting should not do chained calls, e.g., crtc_disable calling
plane_disable. This change was already in my plan actually, but as I had
IOMMU disabled I didn't see it here, and I didn't create this patch yet.

	Gustavo