Re: [PATCH v3 4/4] drm/msm/dpu: fix video mode DSC INTF timing width calculation

[Jonathan Marek <jonathan@marek.ca>]

On 3/19/26 1:31 PM, Alexander Koskovich wrote:
> On Thursday, March 19th, 2026 at 1:23 PM, Jonathan Marek <jonathan@marek.ca> wrote:
> 
...>>
>> The hdisplay calculation in dsi_adjust_pclk_for_compression (which only
>> affects the clock rate) seems to be wrong, and I think Alexander's panel
>> must be running at a 20% lower clock because of it. dsi_timing_setup has
>> the right hdisplay adjustment.
> 
> Checked against downstream and the clocks seem to match more or less:
> 
> downstream:
> pclk: 110070156
> byte: 103190771
> 
> upstream:
> pclk: 110073457
> byte: 103193865
> 
I was curious about this and looked into it a bit (without testing any HW):

- using MIPI_DSI_FMT_RGB101010 dsi_byte_clk_get_rate cancels the effect 
of adjusting with bits_per_component for the byte clk, so the byte clock 
ends up being right
- using DST_FORMAT_RGB101010 DSI pclk is in 30-bit units instead of 
24-bit units, so the pclk ends up being right too (but that only works 
if widebus is enabled)

a recent commit (ac47870fd795) changed the hdisplay calculation in 
dsi_timing_setup to match that in dsi_adjust_pclk_for_compression, but 
only when widebus is enabled.

So things work out if widebus is enabled and MIPI_DSI_FMT_RGB101010 is 
used (note: looks like the only upstream 10-bit panel uses 
MIPI_DSI_FMT_RGB888), otherwise its broken.

AFAICT if you revert ac47870fd795, use MIPI_DSI_FMT_RGB888, and change 
dsi_adjust_pclk_for_compression to divide by 24 instead of 30, then it 
should also work (and won't be dependent on widebus).