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

From: Shuah Khan
Date: Wed Oct 12 2016 - 19:22:59 EST

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@xxxxxxxxxxx>
>> 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

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:

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.

-- Shuah