[PATCH v6 6/7] drm/msm/dsi: update hdisplay calculation for dsi_timing_setup

[Marijn Suijten]

On 2023-05-07 17:27:33, Marijn Suijten wrote:
> On 2023-05-04 15:05:15, Abhinav Kumar wrote:
> > 
> > 
> > On 5/4/2023 2:56 PM, Marijn Suijten wrote:
> > > On 2023-04-12 16:25:20, Jessica Zhang wrote:
> > >> hdisplay for compressed images should be calculated as bytes_per_slice *
> > >> slice_count. Thus, use MSM DSC helper to calculate hdisplay for
> > >> dsi_timing_setup instead of directly using mode->hdisplay.
> > >>
> > >> Changes in v3:
> > >> - Split from previous patch
> > >> - Initialized hdisplay as uncompressed pclk per line at the beginning of
> > >>    dsi_timing_setup as to not break dual DSI calculations
> > >>
> > >> Changes in v4:
> > >> - Moved pclk_per_intf calculations to DSC hdisplay adjustments
> > >>
> > >> Signed-off-by: Jessica Zhang <quic_jesszhan at quicinc.com>
> > >> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
> > >> ---
> > >>   drivers/gpu/drm/msm/dsi/dsi_host.c | 2 +-
> > >>   1 file changed, 1 insertion(+), 1 deletion(-)
> > >>
> > >> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > >> index 508577c596ff..ae966d4e349d 100644
> > >> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> > >> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > >> @@ -952,7 +952,7 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
> > >>   		 * pulse width same
> > >>   		 */
> > >>   		h_total -= hdisplay;
> > >> -		hdisplay /= 3;
> > >> +		hdisplay = msm_dsc_get_pclk_per_intf(msm_host->dsc) / 3;
> > > 
> > > This patch is unfortunately regressing the Sony Xperia XZ3 (sdm845,
> > > single DSI), which will only show garbage when it is applied.
> > > 
> > > Are you sure this is correct, and the helper is returning the right
> > > values?  I'll see if I can help review and validate those later, and
> > > debug if necessary.
> > > 
> > > - Marijn
> > 
> > To help us debug these kind of issues, can you pls point us to your 
> > panel driver?
> 
> https://github.com/SoMainline/linux/commit/b154ea72e6c2ca0d4a33a28cc24e3a762dba4948

I found the fix myself after piecing together the hints provided across
the many different patch series.  This panel driver assigns
slice_count=1 based on downstream's qcom,mdss-dsc-slice-per-pkt = <1>,
but as per the many slice_count-related fixes the latter DT parameter is
a QCOM-specific hardware feature, whereas slice_count is simply the
number of slices per line.

Since a line is a scanline, and that panel has a width of hdisplay=1440
and a slice_width of 720, the number of slices spanning a line is simply
slice_count=hdisplay/slice_width=2.  This makes the panel work again
atop the four-or-so-series without a revert of this patch.

Is it a big ask to request a single, coherent series fixing all uses of
slice_count - and implementing support for slice-per-pkt - instead of
having the patches spread across multiple series?  That makes it much
easier to cover ground here and review this series, as slice_count seems
to be used everywhere where downstream used slice_per_pkt - even I
mistakenly used it after assuming it was the same based on the original
patches.

- Marijn