linux-kernel - Re: [PATCH] exynos-drm: Fix display manager failing to start without IOMMU problem

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Message-ID: <1b2c3b31-7127-af2f-18a2-f3a28567e28d@osg.samsung.com>
Date:   Wed, 12 Oct 2016 17:15:47 -0600
From:   Shuah Khan <shuahkh@....samsung.com>
To:     Inki Dae <inki.dae@...sung.com>, jy0922.shim@...sung.com,
        sw0312.kim@...sung.com, kyungmin.park@...sung.com,
        airlied@...ux.ie, kgene@...nel.org,
        Krzysztof Kozlowski <krzk@...nel.org>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] exynos-drm: Fix display manager failing to start without
 IOMMU problem

On 10/12/2016 05:11 PM, Shuah Khan wrote:

+ Fixing Krzysztof Kozlowski address.

> Hi Inki,
> 
> On 08/15/2016 10:40 PM, Inki Dae wrote:
> 
>>>
>>> okay the very first commit that added IOMMU support
>>> introduced the code that rejects non-contig gem memory
>>> type without IOMMU.
>>>
>>> commit 0519f9a12d0113caab78980c48a7902d2bd40c2c
>>> Author: Inki Dae <inki.dae@...sung.com>
>>> Date:   Sat Oct 20 07:53:42 2012 -0700
>>>
>>>     drm/exynos: add iommu support for exynos drm framework
>>>
> 
> I haven't given up on this yet. I am still seeing the following failure:
> 
> Additional debug messages I added:
> [   15.287403] exynos_drm_gem_create_ioctl() 1
> [   15.287419] exynos_drm_gem_create() flags 1
> 
> [   15.311511] [drm:exynos_drm_framebuffer_init] *ERROR* Non-contiguous GEM memory is not supported.
> 
> Additional debug message I added:
> [   15.318981] [drm:exynos_user_fb_create] *ERROR* failed to initialize framebuffer
> 
> This is what happens:
> 
> 1. exynos_drm_gem_create_ioctl() gets called with EXYNOS_BO_NONCONTIG request
> 2. exynos_drm_gem_create(0 goes ahead and creates the GEM buffers
> 3. exynos_user_fb_create() tries to associate GEM to fb and fails during
>    check_fb_gem_memory_type()
> 
> At this point, there is no recovery and lightdm fails
> 
> xf86-video-armsoc/src/drmmode_exynos/drmmode_exynos.c assumes contiguous
> allocations are not supported in some exynos drm versions: The following
> commit introduced this change:
> 
> https://git.linaro.org/arm/xorg/driver/xf86-video-armsoc.git/commitdiff/3be1f6273441fe95dd442f44064387322e16b7e9
> 
> excerpts from the diff:-       if (create_gem->buf_type == ARMSOC_BO_SCANOUT)
> -               create_exynos.flags = EXYNOS_BO_CONTIG;
> -       else
> -               create_exynos.flags = EXYNOS_BO_NONCONTIG;
> +
> +       /* Contiguous allocations are not supported in some exynos drm versions.
> +        * When they are supported all allocations are effectively contiguous
> +        * anyway, so for simplicity we always request non contiguous buffers.
> +        */
> +       create_exynos.flags = EXYNOS_BO_NONCONTIG;
> 
> There might have been logic on exynos_drm that forced Contig when it coudn't
> support NONCONTIG. At least, that is what this comment suggests. This assumption
> doesn't appear to be a good one and not sure if this change was made to fix a bug.
> 
> After the IOMMU support, this assumption is no longer true. Hence, with IOMMU
> support, latest kernels have a mismatch with the installed xf86-video-armsoc
> 
> This is what I am running into. This leads to the following question:
> 
> 1. How do we ensure exynos_drm kernel changes don't break user-space
>    specifically xf86-video-armsoc
> 2. This seems to have gone undetected for a while. I see a change in
>    exynos_drm_gem_dumb_create() that is probably addressing this type
>    of breakage. Commit 122beea84bb90236b1ae545f08267af58591c21b adds
>    handling for IOMMU NONCONTIG case.
> 
> Anyway, I am interested in getting the exynos_drm kernel side code
> and xf86-video-armsoc in sync to resolve the issue.
> 
> Could you recommend a going forward plan?
> 
> I can submit a patch to xf86-video-armsoc. I am also looking ahead to
> see if we can avoid such breaks in the future by keeping kernel and
> xf86-video-armsoc in sync.
> 
> thanks,
> -- Shuah
>