[Letux-kernel] DSI panels with omapdrm on 4.20-rc

H. Nikolaus Schaller hns at goldelico.com
Thu Dec 20 12:57:06 CET 2018

Hi Tomi,

> Am 20.12.2018 um 09:21 schrieb Tomi Valkeinen <tomi.valkeinen at ti.com>:
> On 19/12/18 18:36, H. Nikolaus Schaller wrote:
>> Hi Tomi,
>>> Am 19.12.2018 um 10:30 schrieb Tomi Valkeinen <tomi.valkeinen at ti.com>:
>>> On 18/12/18 20:09, H. Nikolaus Schaller wrote:
>>>>> Comparing it to the (mostly) working kernel, I found out that the bus
>>>>> flags are again broken. I attached a quick hack patch that seems to fix
>>>>> them, and with that I get a working 400x400 plane, but underflows with
>>>>> full-screen plane.
>>>>> I couldn't quite figure out how to fix the bus-flags correctly, though.
>>>> Hm. For me this patch does not make a difference.
>>>> But I think we are close to a solution.
>>> Ok... Well, the VC stuff works ok for me, as far as I see.
>>> I pushed my hacky test branch to:
>>> git://git.kernel.org/pub/scm/linux/kernel/git/tomba/linux.git
>>> 4.20/omap5-video-dsi-test
>>> It has one additional fix "fix dsi depopulate", which is needed if you
>>> want to unload modules.
>> It seems as if that one already makes the difference!
> You mean it works now for you?


>>> The only problem with my branch are FIFO underflows. Apparently these
>>> were present on older kernels too, and is probably somehow related to
>>> horizontal blanking. 1080x1920 plane causes underflows, but 1000x1920
>>> does not.
>> I haven't seen that but it might be that if horizontal blanking is
>> too short, it might not be enough to send long DCS commands.
> Hmm I don't think it's related to DCS, as this happens when no commands
> are being sent. And the DSI side shouldn't affect DISPC, where the
> underflows are coming from.
>> So in summary I have added these patches not yet in v4.20-rc7 (plus the panel driver):
>> b2b80dbeff3a fix dsi depopulate
>> 2ef5e09c79d9 drm/omap: hackfix dsi bus flags
>> b8aedc2b8295 drm/omap: fix crash in DSI debug dumps
>> 5cceb44e03e3 drm/omap: add support for manually updated displays
>> 87dfb765c3be drm/omap: add framedone interrupt support
>> 50f581c97fbe drm/omap: fix incorrect union usage
>> 977e0c2e641f drm/omap: don't check dispc timings for DSI
>> f62952e37eae drm/omap: use DRM_DEBUG_DRIVER instead of CORE
>> Do you plan to get these fixes already into v4.20.0?
> Are you sure you're on -rc7? At least "drm/omap: fix incorrect union
> usage" is in -rc7.

Well, I am on v4.20-rc7 but after rebasing a private copy of all the patches
collected in the last weeks.

Looks as if I had an older version of "drm/omap: fix incorrect union usage"
in my branch so that the rebase to -rc7 did not melt it completely away.
So there remained an additional safety test in this (local) patch.

BR and thanks,

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