[PATCH v2 4/9] drm/panthor: Implement optional reset

[Philipp Zabel]

On Di, 2025-03-25 at 15:27 +0100, Marek Vasut wrote:
> On 3/25/25 3:12 PM, Philipp Zabel wrote:
> > On Mo, 2025-03-24 at 20:05 +0100, Marek Vasut wrote:
> > > On 3/24/25 9:43 AM, Boris Brezillon wrote:
> > > 
> > > [...]
> > > 
> > > > > @@ -563,6 +585,7 @@ int panthor_device_suspend(struct device *dev)
> > > > >    
> > > > >    	panthor_devfreq_suspend(ptdev);
> > > > >    
> > > > > +	reset_control_assert(ptdev->resets);
> > > > 
> > > > Hm, that might be the cause of the fast reset issue (which is a fast
> > > > resume more than a fast reset BTW): if you re-assert the reset line on
> > > > runtime suspend, I guess this causes a full GPU reset, and the MCU ends
> > > > up in a state where it needs a slow reset (all data sections reset to
> > > > their initial state). Can you try to move the reset_control_[de]assert
> > > > to the unplug/init functions?
> > > The reset on the MX95 is not really a reset, it is clear-only
> > > set-never-again bit which goes only one way, the "unreset" way, so I
> > > don't think this has any impact.
> > 
> > This sounds like the bit is initially set to 1 (reset asserted) and can
> > be cleared by writing 0 (once, to deassert the reset). But in the
> > reset-simple patch it looks to be the other way around (active_low =
> > true)?
> > 
> > If the reset control can't be asserted again on this hardware, it would
> > be better to have custom driver that doesn't implement the .assert()
> > callback at all.
> Maybe the reset-simple driver can be extended with some mode of 
> operation like this instead , to make it skip assert once deasserted , 
> for specific reset controllers ?

How about a second reset_control_ops struct without .assert, selected
in reset_simple_probe() by a new flag in reset_simple_devdata.

regards
Philipp