Re: [Freedreno] [PATCH v10 8/8] drm/msm/dsi: update hdisplay calculation for dsi_timing_setup

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On 5/16/2023 3:45 PM, Marijn Suijten wrote:
On 2023-05-16 11:18:17, Jessica Zhang wrote:
On 5/14/2023 2:29 PM, Marijn Suijten wrote:
On 2023-05-12 14:32:18, 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.

As mentioned in review on an earlier revision, is there any sort of
clarification you can provide here to explain the cases where
hdisplay!=bytes_per_line?  That goes a long way towards justifying this
change.  Thanks!

Hi Marijn,

Sorry for not responding to this in the earlier revision, I think I
missed the original comment.

Please correct me if I'm wrong, but I'm guessing the question here is
why we can't keep the hdisplay adjustment as `hdisplay /= 3` and have to
go out of our way to recalculate hdisplay before doing the `/ 3`.

This is because the original adjustment only works for BPP = 8. By using
the msm_dsc_get_bytes_per_line() here, we can generalize this adjustment
to work for cases where BPP != 8.

I am fully aware that the original computation only works for BPP=8 and
even mentioned so in v7 review [1].  The question / request is instead
to include such context in your commit message, rather than the
nondescriptive "should be calculated as" -> who says that and why?
Stating that the current approach was only working for BPP=8 (hence why
currently tested panels are working fine) but that this isn't a
long-term solution if we starts upporting other BPP is a proper
justification to make this change.

Sounds good, will add this to the commit message.

Thanks,

Jessica Zhang


[1]: https://lore.kernel.org/linux-arm-msm/ju7647tlogo25fnhswgp7zn67syvsjy2ldjugvygh3z4rxtdrx@kb76evjvulgw/

Thanks,

Thanks for looking into improving this!

- Marijn



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