Re: [Freedreno] [RFC PATCH 00/13] drm/msm: Add Display Stream Compression Support

[Vinod Koul <vkoul@kernel.org>]

On 26-05-21, 09:00, Jeffrey Hugo wrote:
> On Tue, May 25, 2021 at 11:46 PM Vinod Koul <vkoul@kernel.org> wrote:
> > On 21-05-21, 08:09, Jeffrey Hugo wrote:
> > > On Fri, May 21, 2021 at 6:50 AM Vinod Koul <vkoul@kernel.org> wrote:
> > > >
> > > > Display Stream Compression (DSC) compresses the display stream in host which
> > > > is later decoded by panel. This series enables this for Qualcomm msm driver.
> > > > This was tested on Google Pixel3 phone which use LGE SW43408 panel.
> > > >
> > > > The changes include adding DT properties for DSC then hardware blocks support
> > > > required in DPU1 driver and support in encoder. We also add support in DSI
> > > > and introduce required topology changes.
> > > >
> > > > In order for panel to set the DSC parameters we add dsc in drm_panel and set
> > > > it from the msm driver.
> > > >
> > > > Complete changes which enable this for Pixel3 along with panel driver (not
> > > > part of this series) and DT changes can be found at:
> > > > git.linaro.org/people/vinod.koul/kernel.git pixel/dsc_rfc
> > > >
> > > > Comments welcome!
> > >
> > > This feels backwards to me.  I've only skimmed this series, and the DT
> > > changes didn't come through for me, so perhaps I have an incomplete
> > > view.
> >
> > Not sure why, I see it on lore:
> > https://lore.kernel.org/dri-devel/20210521124946.3617862-3-vkoul@kernel.org/
> >
> > > DSC is not MSM specific.  There is a standard for it.  Yet it looks
> > > like everything is implemented in a MSM specific way, and then pushed
> > > to the panel.  So, every vendor needs to implement their vendor
> > > specific way to get the DSC info, and then push it to the panel?
> > > Seems wrong, given there is an actual standard for this feature.
> >
> > I have added slice and bpp info in the DT here under the host and then
> > pass the generic struct drm_dsc_config to panel which allows panel to
> > write the pps cmd
> >
> > Nothing above is MSM specific.. It can very well work with non MSM
> > controllers too.
> 
> I disagree.
> 
> The DT bindings you defined (thanks for the direct link) are MSM
> specific.  I'm not talking (yet) about the properties you defined, but
> purely from the stand point that you defined the binding within the
> scope of the MSM dsi binding.  No other vendor can use those bindings.
> Of course, if we look at the properties themselves, they are prefixed
> with "qcom", which is vendor specific.
> 
> So, purely on the face of it, this is MSM specific.
> 
> Assuming we want a DT solution for DSC, I think it should be something
> like Documentation/devicetree/bindings/clock/clock-bindings.txt (the
> first example that comes to mind), which is a non-vendor specific
> generic set of properties that each vendor/device specific binding can
> inherit.  Panel has similar things.
> 
> Specific to the properties, I don't much like that you duplicate BPP,
> which is already associated with the panel (although perhaps not in
> the scope of DT).  What if the panel and your DSC bindings disagree?
> Also, I guess I need to ask, have you read the DSC spec?  Last I
> looked, there were something like 3 dozen properties that could be
> configured.  You have five in your proposed binding.  To me, this is
> not a generic DSC solution, this is MSM specific (and frankly I don't
> think this supports all the configuration the MSM hardware can do,
> either).

I would concede the point that DT is msm specific. I dont disagree on
making them a common dsc biding which anyone can use. I think your idea
does have merits...

I am still not sure who should include these properties, would it be the
panel or host. Either would work and rest of the system can use these
properties...

-- 
~Vinod