[RFC PULL] Add Display Support for Qualcomm SDM845

[Rob Clark]

On Wed, Feb 14, 2018 at 3:30 AM, Daniel Stone <daniel at fooishbar.org> wrote:
> Hi Rob,
>
> On 13 February 2018 at 20:00, Rob Clark <robdclark at gmail.com> wrote:
>> On Tue, Feb 13, 2018 at 2:18 PM, Sean Paul <seanpaul at chromium.org> wrote:
>>> Qualcomm has been working for the past few weeks on forward porting their
>>> downstream drm driver from 4.14 to mainline. Please consider this PR as a
>>> request for review, rather than an attempt at mainlining the code as it
>>> currently stands. The goal is get this driver in shape over the next coming
>>> months.
>>
>> just so others aren't confused, s/sde/dpu/g in the list below (we did
>> our DAL->DC rename before sending first RFC :-P)
>
> Heh, and it is quite a bit of code to dig through. I haven't yet got a
> chance to fully check it out.
>
>>> - include/uapi/drm/msm_drm_pp.h needs opensource userspace (or removal)
>
> We don't really have a good story for pixel-processing API anywhere tbh.
>
>> To add to that, a few things I've noticed (but I've mostly only gotten
>> as far as the front-end of the pipeline, ie. dpu_plane):
>>
>>  - It looks like, as was the case with mdp4/mdp5 (and really most other hw)
>>    there are still unequal capabilities for planes (ie. some can do YUV,
>>    scaling, etc).
>>
>>    But drm-hwc (or weston) isn't going to know about that, so I think we'll
>>    need to add support for dynamically assigning dpu_plane::pipe, similar
>>    to what mdp5 does w/ plane<->hwpipe.  (Which I actually added specifically
>>    for drm-hwc ;-))
>
> Formats/modifiers we do at least get per-plane. We won't know about
> scaling, but at least Weston will go through trying each plane in
> sequence until it finds one which accepts the configuration. Could HWC
> do something like that with atomic, or does it rely on coming up with
> a plan first rather than the brute-force testing approach? I haven't
> seen its planner at all recently I'm afraid.
>
>>  - I *think* we also need the same trick for combining mixers under one CRTC
>>    for 4k modes too?
>
> This one I guess you can't get around though. Can they still run from
> the one plane, or do you secretly consume two planes?
>

I think it is still the case, like mdp5, that you need two hw pipes..
but actually it gets more crazy, since there are some cases where two
planes could share a hw pipe.  Not sure that weston or drm-hwc is
going to have much hope in being able to deal with that, so I think
virtualizing the planes and crtcs is the better route.

BR,
-R

>>  - in dpu_plane, and perhaps elsewhere, userspace pointers for things like CSC
>>    and scaling coefficients need to be annotated w/ __user.  (Except the should
>>    probably be blob properties instead.. and we probably need to strip out the
>>    custom properties and re-introduce them separately with some userspace +
>>    review.)
>
> It'd be good to know if the CSC could use the CRTC GAMMA_LUT -> CTM ->
> DEGAMMA_LUT properties, if they were moved over to planes. (And if
> not, why not; if there's any functionality missing from those, what it
> is, etc.)
>
> Cheers,
> Daniel