Re: [PATCH] drm/msm/dsi: Restore widebus calculation for CMDMode panels

[Pengyu Luo]

On Fri, Mar 20, 2026 at 9:59 AM Dmitry Baryshkov
<dmitry.baryshkov@xxxxxxxxxxxxxxxx> wrote:
>
> On Thu, Mar 12, 2026 at 01:10:07PM +0800, Pengyu Luo wrote:
> > On Thu, Mar 12, 2026 at 6:31 AM Marijn Suijten
> > <marijn.suijten@xxxxxxxxxxxxxx> wrote:
> > >
> > > Commit ac47870fd795 ("drm/msm/dsi: fix hdisplay calculation when
> > > programming dsi registers") makes a false and ungrounded statement that
> > > "Since CMD mode does not use this, we can remove !(msm_host->mode_flags
> > > & MIPI_DSI_MODE_VIDEO) safely." which isn't the case at all.
> > > dsi_timing_setup() affects both command mode and video mode panels, and
> > > by no longer having any path that sets bits_per_pclk = 48 (contrary to
> > > the updated code-comment) all DSI DSC panels on SM8350 and above (i.e.
> > > with widebus support) regress thanks to this patch.
> > >
> > > The entire reason that video mode was originally omitted from this code
> > > path is because it was never tested before; any change that enables
> > > widebus for video mode panels should not regress the command mode path.
> > >
> > > Thus add back the path allows 6 bytes or 48 bits to be sent per pclk
> > > on command mode DSI panels with widebus, restoring the panel on devices
> > > like the Sony Xperia 1 III and upwards.
> > >
> > > Fixes: ac47870fd795 ("drm/msm/dsi: fix hdisplay calculation when programming dsi registers")
> > > Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
> > > ---
> >
> > Apologies, I messed up, I had sent the same fixes days ago.
> > https://lore.kernel.org/linux-arm-msm/20260307111250.105772-2-mitltlatltl@xxxxxxxxx/
> >
> > > In addition I can't say I understand the original commit message
> > > at all; it mentions a BPC=10 mode however the highest format that
> > > mipi_dsi_pixel_format_to_bpp supports is RGB888 thus it won't
> > > ever return anything above 24, which is the original amount the
> > > non-command-mode path defaulted to (regardless of widebus)...  Was that
> > > patch doing anything for video mode at all?
> > >
> >
> > RGB888 is the dst bpc, which is tied to qcom,mdss-dsi-bpp in the downstream.
> >
> > Actually, we should use src bpc here, another fixe
> > https://lore.kernel.org/linux-arm-msm/20260307111250.105772-1-mitltlatltl@xxxxxxxxx/
>
> I'm really torn between your two patchsets here.
>
> Marijn, Pengyu, what are your testing platforms and are you testing
> video or command mode panels?
>

SM8750, I am testing on a native 10-bit video mode panel.

My thoughts are we should restore 6 for the cmd panel, and we should
fix video mode too.
As I mentioned, I overlooked something, I thought the cmd panel didn't
use the value, which
made the value for the cmd panel wrong. So we can restore it for the
cmd panel (though I can't say why 6).

Best wishes,
Pengyu