Re: [PATCH] drm/msm/dpu: always program dsc active bits

[Marijn Suijten]

On 2023-04-11 16:45:34, Abhinav Kumar wrote:
[..]
> > Does this flush all DSCs programmed in CTL_DSC_FLUSH as set above?  That
> > is currently still in `if (cfg->dsc)` and never overwritten if all DSCs
> > are disabled, should it be taken out of the `if` to make sure no DSCs
> > are inadvertently flushed, or otherwise cache the "previous mask" to
> > make sure we flush exactly the right DSC blocks?
> > 
> 
> Yes, DSC flush is hierarchical. This is the main DSC flush which will 
> enforce the flush of the DSC's we are trying to flush in the 
> CTL_DSC_FLUSH register.

That's what I was thinking, thanks for confirming.

> So if DSC was active, the CTL_FLUSH will only enforce the flush of the 
> DSC's programmed in CTL_DSC_FLUSH
> 
> If DSC is not active, we still need to flush that as well (that was the 
> missing bit).
> 
> No need to cache previous mask. That programming should be accurate in 
> cfg->dsc already.

This kind of implicit dependency warrants a comment at the very least.

What happens if a device boots without DSC panel connected?  Will
CTL_DSC_FLUSH be zero and not (unnecessarily, I assume) flush any of the
DSC blocks?  Or could this flush uninitialized state to the block?

- Marijn