Re: [PATCH] drm/msm/disp/dpu: consider SSPP line width during mode valid

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On Tue, Mar 31, 2026 at 12:27:19AM +0530, Vishnu Saini wrote:
> On Mon, Mar 30, 2026 at 09:39:31PM +0300, Dmitry Baryshkov wrote:
> > On Tue, Mar 31, 2026 at 12:00:07AM +0530, Vishnu Saini wrote:
> > > On Sun, Mar 29, 2026 at 02:24:53AM +0200, Dmitry Baryshkov wrote:
> > > > On Sat, Mar 28, 2026 at 10:45:35PM +0530, Vishnu Saini wrote:
> > > > > Few targets have lesser SSPP line width compared to mixer width,
> > > > > SSPP line width also needs to be considered during mode valid
> > > > > to avoid failures during atomic_check.
> > > > 
> > > > Technically this is not correct. There is no requirement for the
> > > > planes to cover the whole CRTC. Nor is there a requirement to use only 2
> > > > rectangles to cover the screen. As such, it is perfectly fine in
> > > > mode_valid, if CRTC is wider than 2x max_linewidth. It would be an error
> > > > if the user tries to stretch 2 rectangles in such a case.
> > > 
> > > This is to fix an issue with 5k monitor on rb3gen2, since SSPP maxlinewidth is 2400
> > > it can't cover the whole 5k buffer in left right split mode.
> > > Do we need to fix it from drm backend by dividing 5k buffer into 2 planes and 
> > > use 2 pipes in split mode.
> > 
> > Quad pipe is pending for 7.2, most likely. However, I think, instead you
> > should teach compositor that if the commit fails, it should retry with
> > the lower resolution (it might require somethi g like -E2BIG from te
> > commit).
> Yes, from driver we are returning "-E2BIG" during atomic_check.
> Thank you for the clarity, will try to fix it from compositor.

Just to point out: it's not different from the driver not being able to
perform the atomic commit for any other reason. For example, if card has
3 outputs but can support only 2 concurrent outputs, then each connector
will still have a list of valid modes, but trying to enable outputs on
all three of them would still fail (or trying to enable high-enough
resolution on all three, if that removes a possible question of limiting
number of outputs by other means).

>  
> > > 4 SSPP rects --> 2 LMs --> 3d_mux --> DP
> > >  
> > > > > 
> > > > > Signed-off-by: Vishnu Saini <vishnu.saini@oss.qualcomm.com>
> > > > > ---
> > > > >  drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 12 ++++++++----
> > > > >  1 file changed, 8 insertions(+), 4 deletions(-)
> > > > > 
> > > > 
> > > > -- 
> > > > With best wishes
> > > > Dmitry
> > 
> > -- 
> > With best wishes
> > Dmitry

-- 
With best wishes
Dmitry