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

[Abhinav Kumar]

On 4/12/2023 12:24 AM, Marijn Suijten wrote:
> 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.

Sure.

> 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?

If we bootup without DSC panel connected, the kernel's cfg->dsc will be 
0 and default register value of CTL_DSC_FLUSH will be 0 so it wont flush 
any DSC blocks. Sure, as I wrote in the other response, we can move this 
to reset_intf_cfg later when the other pieces are fixed. And leave a 
FIXME here.

> - Marijn