Atomic mode-setting drivers

[Alex Deucher]

On Fri, Mar 4, 2016 at 4:59 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Fri, Mar 04, 2016 at 06:08:16PM +0000, Emil Velikov wrote:
>> On 4 March 2016 at 16:32, Daniel Vetter <daniel at ffwll.ch> wrote:
>> > Adding relevant mailing lists and people. Please don't send private
>> > mails to maintainers ;-)
>> >
>> > On Fri, Mar 4, 2016 at 1:47 PM, Chih-Wei Huang <cwhuang at android-x86.org> wrote:
>> >> Hi Daniel,
>> >> This is the Android-x86 project.
>> >> I'm looking for info about atomic mode-setting drivers
>> >> and then found your presentation at
>> >> http://www.x.org/wiki/Events/XDC2015/Program/xdc-2015.pdf
>> >>
>> >> Especially page 16 talks about the Android support,
>> >> exactly what I want.
>> >>
>> >> It said "no one has an open-source atomic hwc".
>> >> Actually there is one in the AOSP 6.0 release:
>> >>
>> >> https://android.googlesource.com/platform/external/drm_hwcomposer
>> >>
>> >> It's developed by the Chromium team.
>> >> An update repo is here:
>> >> https://chromium.googlesource.com/chromiumos/drm_hwcomposer
>> >
>> > Yup, my presentation is already outdated - the latest one for LCA2016
>> > mentions that hwc exists.
>> >
>> >> Contributing instructions are here:
>> >> https://sites.google.com/a/chromium.org/dev/contributing-to-drm_hwcomposer
>> >>
>> >> We are trying to enable the drm_hwcomposer for Android-x86.
>> >> However, it requires atomic mode-setting drivers
>> >> which seems are not ready in the vanilla kernel 4.4,
>> >> the kernel we are using now.
>> >>
>> >> Unfortunately none of us is an expert of kernel drm drivres.
>> >> Could you give me a brief status of the
>> >> current atomic mode-setting drivers in vanilla kernel?
>> >> What are still missing? fences? deadlock?
>> >> More important, how much effort do we need
>> >> to make them work with AOSP's drm_hwcomposer?
>> >
>> > There's a pile of drivers, but for classic x86 desktop only i915.ko,
>> > and that is still not yet enabled by default. i915.nuclear_pageflip=1
>> > will give you experimental atomic support but not sure whether that's
>> > good enough for hwcomposer.
>> >
>> > Fences are being worked on in upstream kernel, but nothing to show
>> > yet.. Otherwise I don't know what's all needed to make it, I haven't
>> > had a chance to play around with it yet.
>> >
>> Let's not forget the new AMDGPU code that, according to the summary
>> [1], adds ATOMIC support for newer AMD hardware.
>>
>> Chih-Wei, there might be an updated branch somewhere you can grab,
>> sadly I did not find any. Thus you might have to pick the patches off
>> the mailing list, unless we have a patchwork instance for it somewhere
>> ?
>
> amdgpu DAL rewrite isn't really atomic unfortunately. I can't tell you how
> un-atomic it is since it's such a maze, but there's not much chance it is
> useful as an atomic driver.

Code complexities and internal abstractions aside, we've implemented
the API and tested it and it appears to work.  What sort of additional
semantics does atomic imply that you don't think DAL would handle?

Alex

> -Daniel
>
>>
>> >>
>> >> More discussion about it can be found in
>> >> our devel group:
>> >> https://groups.google.com/d/msg/android-x86-devel/RErWaXk3b7g/g_OSPGf4AwAJ
>> >
>> > Please include that mailing list too, to make sure everyone is on board.
>> >
>> Not sure why, yet that mailing list is closed for public eyes. Last
>> time I checked one has to be invited to read or write to it :-(
>> Props to Chih-Wei I'm on it, although others are sure to get the short
>> end of the stick.
>>
>> Regards,
>> Emil
>>
>> [1] https://lists.freedesktop.org/archives/dri-devel/2016-February/100524.html
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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