[Intel-gfx] [PATCH] drm/i915/display: Return correct err code for bpc < 0

[Manasi Navare]

Hi Ville and Ankit,

I actually do not think this is a problem with the DSC logic, but it
is a problem with the intel_dp_link_compute_config() where we should
do something if max_bpp is 0 instead of just returning a -EINVAL
directly.
My question here:
- In case of PCON, yuv format, is it a valid case to have max bpp set to 0?
- This is where I am seeing it as set to 0
- If it isnt then the problem is probably where it computes max bpp
for hdmi case for yuv format

Manasi

On Tue, Apr 18, 2023 at 7:54 AM Ville Syrjälä
<ville.syrjala at linux.intel.com> wrote:
>
> On Tue, Apr 18, 2023 at 08:09:16PM +0530, Nautiyal, Ankit K wrote:
> >
> > On 4/18/2023 6:16 PM, Ville Syrjälä wrote:
> > > On Mon, Apr 17, 2023 at 03:48:12PM -0700, Manasi Navare wrote:
> > >> Hi Ville,
> > >>
> > >> Could you suggest how to handle the intel_dp_link_compute_config()
> > >> when the max_bpp is returned as 0, currently
> > >> it just exits the loop and returns a -EINVAL and this triggers the DSC path.
> > >> While we should be completely failing the modeset and encoder_config
> > >> in this case instead of trying DSC, correct?
> > > The DSC path needs to handle the bpp limits correctly:
> > > 1. Take the baseline limits already computed
> > > 2. Further restrict them based on sink/source DSC capabilities/etc.
> > > 3. Make sure the uncompressed bpp value chosen is between the min/max
> >
> > I have some older patch to try similar thing [1]. We try to iterate over
> > bpc to find pipe_bpp in the limits, then try to find out compressed_bpp.
> >
> > But if intel_dp_max_bpp returns 0, limits.max_bpp is set to 0, so we
> > discard this for dsc case and re-calculate the limits.max_bpp?
>
> You shouldn't discard anything. DSC should take the already computed
> limits and potentially just shrink them further based on DSC specific
> constraints.
>
> Or is there some weird case where DSC would allow lower/higher bpp
> than what our uncompressed bpp limits declare?
>
> >
> >
> > [1] https://patchwork.freedesktop.org/patch/519346/?series=111391&rev=3
> >
> > >
> > >> Manasi
> > >>
> > >> On Thu, Apr 13, 2023 at 8:23 AM Manasi Navare <navaremanasi at chromium.org> wrote:
> > >>> On Tue, Apr 11, 2023 at 10:22 PM Ville Syrjälä
> > >>> <ville.syrjala at linux.intel.com> wrote:
> > >>>> On Tue, Apr 11, 2023 at 05:07:01PM -0700, Manasi Navare wrote:
> > >>>>> On Tue, Apr 11, 2023 at 10:42 AM Ville Syrjälä
> > >>>>> <ville.syrjala at linux.intel.com> wrote:
> > >>>>>> On Tue, Apr 11, 2023 at 05:34:08PM +0000, Manasi Navare wrote:
> > >>>>>>> In the function intel_dp_max_bpp(), currently if bpc < 0 in case of error,
> > >>>>>>> we return 0 instead of returning an err code of -EINVAL.
> > >>>>>>> This throws off the logic in the calling function.
> > >>>>>> What logic? The caller doesn't expect to get an error.
> > >>>>> If this returns a 0, we end up using limits.max_bpp = 0 and in
> > >>>>> intel_dp_compute_link_config_wide(),
> > >>>>> since max_bpp is 0, it exits this for loop:
> > >>>>>
> > >>>>> for (bpp = limits->max_bpp; bpp >= limits->min_bpp; bpp -= 2 * 3) and returns
> > >>>>> -EINVAL which then wrongly goes to enable DSC even when link BW is
> > >>>>> sufficient without DSC.
> > >>>> And how woud max_bpp<0 prevent that?
> > >>>>
> > >>>> The real problem seems to be that the DSC code totally
> > >>>> ignores bpp limits.
> > >>> Hi Ville,
> > >>>
> > >>> So I see a few concerns/questions:
> > >>> - Why is the Max bpp value 0 in intel_dp_max_bpp, is that a valid case
> > >>> and how should our link configurations handle that case when max_bpp
> > >>> is 0?
> > >>> - This is happening in a bug I am looking at with HDMI PCON, @Ankit
> > >>> Nautiyal  have we ever seen something similar where max_bpp for HDMi
> > >>> PCON
> > >>> is returned 0?
> > >>> - I dont think its a problem with DSC code, but rather
> > >>> intel_dp_compute_link_config() outer for loop where we vary
> > >>> from max_bpp to min_bpp and see if any bpp works with available link
> > >>> bw, how should we handle this when max_bpp = 0 if you are saying thats
> > >>> a valid case?
> > >>> - In this patch if I return -EINVAL instead of 0, then atleast the
> > >>> entire encoder_config will fail and that will fail the modeset, since
> > >>> it assumes max_bpp cannot be 0
> > >>>
> > >>> Could you please help answer above concerns and how to handle max bpp
> > >>> = 0 case if that is valid? This patch is simply making that invalid
> > >>> resulting into modeset failure
> > >>>
> > >>> Manasi
> > >>>> --
> > >>>> Ville Syrjälä
> > >>>> Intel
>
> --
> Ville Syrjälä
> Intel