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

[Aradhya Bhatia]

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.

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(-)
>