Re: [PATCH v6 03/12] drm/bridge: cdns-dsi: Fix phy de-init and flag it so

[Dmitry Baryshkov]

On Mon, Jan 13, 2025 at 09:09:11PM +0530, Aradhya Bhatia wrote:
> Thank you for reviewing the patches, Dmitry.
> 
> On 1/13/25 15:10, Dmitry Baryshkov wrote:
> > On Sun, Jan 12, 2025 at 12:57:29AM +0530, Aradhya Bhatia wrote:
> >> From: Aradhya Bhatia <a-bhatia1@xxxxxx>
> >>
> >> The driver code doesn't have a de-initialization path as yet, and so it
> >> does not clear the phy_initialized flag while suspending. This is a
> >> problem because after resume the driver looks at this flag to determine
> >> if a Phy re-initialization is required or not. It is in fact required
> >> because the hardware is resuming from a suspend, but the driver does not
> >> carry out any re-initialization causing the D-Phy to not work at all.
> >>
> >> Add the counterpart of phy_power_on(), that is phy_power_off() from the
> >> _bridge_disable() and clear the flags so that the Phy can be initialized
> >> again when required.
> >>
> >> Move the Phy initialization from _bridge_enable() to _resume(), and
> >> de-initialize during the _suspend() - so that the phy_{init, exit}()
> >> take place once every resume/suspend cycle.
> > 
> > Is it okay to call phy_init() before writing MCTL_DPHY_CFG0 ?
> 
> The phy_init() is a no-op when we look at the D-Phy driver, which does
> not implement the _init() hook at all. So, in this case, all phy_init()
> call ever manages to do is book-keeping. Book-keeping that isn't
> required to be done every time we do a bridge enable/disable.
> But despite the no-op nature of the call, I guess it would still not
> make sense to call it before the reset assert done in MCTL_DPHY_CFG0.

Yes, please.

> Instead of moving it to resume(), I can keep phy_init() as is, and add
> phy_exit() in the bridge disable path, instead of the suspend path.
> 
> 
> Regards
> Aradhya
> 
> > 
> >>

> >> The order of calls still remains the same. phy_init() needs to be called
> >> before phy_power_on() - which happens still. What this patch changes is
> >> the frequency of the phy_init() call. Instead of it being called once
> >> every bridge enable/disable cycle, it is now being called once every
> >> resume/suspend cycle. This move has been considered safe after numerous
> >> tests with the hardware.
> >>
> >> Fixes: fced5a364dee ("drm/bridge: cdns: Convert to phy framework")
> >> Signed-off-by: Aradhya Bhatia <a-bhatia1@xxxxxx>
> >> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@xxxxxxxxx>
> >> ---
> >>  drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 10 ++++++++--
> >>  1 file changed, 8 insertions(+), 2 deletions(-)
> > 

-- 
With best wishes
Dmitry