[PATCH v6 07/14] drm/bridge: analogix_dp: Add support to get panel from the DP AUX bus

[Damon Ding]

Hi Doug,

On 2025/1/24 11:13, Doug Anderson wrote:
> Hi,
> 
> On Thu, Jan 23, 2025 at 3:25 AM Dmitry Baryshkov
> <dmitry.baryshkov at linaro.org> wrote:
>>
>> On Thu, Jan 23, 2025 at 06:07:40PM +0800, Damon Ding wrote:
>>> The main modification is moving the DP AUX initialization from function
>>> analogix_dp_bind() to analogix_dp_probe(). In order to get the EDID of
>>> eDP panel during probing, it is also needed to advance PM operaions to
> 
> nit: s/operaions/operations
> 

I will fix it in the next version.

> 
>>> ensure that eDP controller and phy are prepared for AUX transmission.
>>
>> This doesn't sound right. Per the documentation of
>> drm_dp_aux::transfer(), the device should power itself up if transfer()
>> is called when it is powered off. The caller must only ensure that the
>> panel is on.
>>
>> Doug, what's your opinion?
> 
> I think maybe the CL description is a bit confusing, but looking at
> the patch I think that the general idea is correct. drm_dp_aux_init()
> is expected to be called in probe() and not in bind(). ...and in order
> for it to work then pm_runtime needs to be enabled at probe and not at
> bind. So both of those two things that this patch does are (in my
> opinion) correct.
> 
> 
>>> In addtion, add a new function analogix_dp_remove() to ensure symmetry
>>> for PM operations.
>>>
>>> Signed-off-by: Damon Ding <damon.ding at rock-chips.com>
>>>
>>> ---
>>>
>>> Changes in v4:
>>> - Use done_probing() to call drm_of_find_panel_or_bridge() and
>>>    component_add() when getting panel from the DP AUX bus
>>>
>>> Changes in v5:
>>> - Advance PM operations to make eDP AUX work well
>>>
>>> Changes in v6:
>>> - Use devm_pm_runtime_enable() instead of devm_add_action_or_reset()
>>> - Add a new function analogix_dp_remove() to ensure symmetry for PM
>>>    operations
>>> ---
>>>   .../drm/bridge/analogix/analogix_dp_core.c    | 57 ++++++++++---------
>>>   .../gpu/drm/rockchip/analogix_dp-rockchip.c   |  4 ++
>>>   include/drm/bridge/analogix_dp.h              |  1 +
>>>   3 files changed, 34 insertions(+), 28 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
>>> index 8251adfce2f9..30da8a14361e 100644
>>> --- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
>>> +++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
>>> @@ -1658,14 +1658,42 @@ analogix_dp_probe(struct device *dev, struct analogix_dp_plat_data *plat_data)
>>>        }
>>>        disable_irq(dp->irq);
> 
> not related to your patch, but probably needs to be a prerequisite of
> your patch: instead of calling disable_irq() here, you should OR in
> "IRQF_NO_AUTOEN" to the "irq_flags" of devm_request_threaded_irq().
> That not only closes a potential race condition but also makes all the
> error handling much more robust.
> 

Yes, it is nice to set the IRQF_NO_AUTOEN flag rather than calling the 
disable_irq().

> 
>>> +     dp->aux.name = "DP-AUX";
>>> +     dp->aux.transfer = analogix_dpaux_transfer;
>>> +     dp->aux.dev = dp->dev;
>>> +     drm_dp_aux_init(&dp->aux);
> 
> FWIW: I would highly encourage you to (in a separate patch) add
> wait_hpd_asserted() support here. It is deprecated to not implement
> wait_hpd_asserted(). See the definition of "wait_hpd_asserted" in
> "struct drm_dp_aux" if you're going to support eDP panels.
> 

Indeed, the &drm_dp_aux.wait_hpd_asserted() help confirm the HPD state 
before doing AUX transfers. I will add it in the next version.

> 
>>> +     if (IS_ENABLED(CONFIG_PM)) {
> 
> Do we really truly need this? Is there anyone actually using this
> driver without "CONFIG_PM", or can we just assume CONFIG_PM. For the
> most part drivers I've interacted with just assume CONFIG_PM and
> they're a lot simpler because of it. If there's truly a need then we
> can keep this complexity, but I'd rather wait until there is a user.
> Maybe you could add this as a dependency in the Kconfig if needed.
> 

I would also like to remove the CONFIG_PM related check, which would 
make the code more concise. And I believe that it would be a good idea 
to remove it and wait until there is a user who actually needs it.

> 
>>> +             pm_runtime_use_autosuspend(dp->dev);
>>> +             pm_runtime_set_autosuspend_delay(dp->dev, 100);
>>> +             ret = devm_pm_runtime_enable(dp->dev);
>>> +             if (ret)
>>> +                     goto err_disable_pm_runtime;
>>> +     } else {
>>> +             ret = analogix_dp_resume(dp);
>>> +             if (ret)
>>> +                     goto err_disable_clk;
> 
> IMO: if analogix_dp_resume() succeeds, use devm_add_action_or_reset()
> to have a function call analogix_dp_suspend(). Then you can keep using
> "devm" for everything and totally get rid of the need for the
> analogix_dp_remove() function.
> 

It may be better to drop the 'complex' check about CONFIG_PM and just 
keep using 'devm' as mentioned above.

> 
>>> +     }
>>> +
>>>        return dp;
>>>
>>> +err_disable_pm_runtime:
>>> +     pm_runtime_dont_use_autosuspend(dp->dev);
> 
> You don't need to call pm_runtime_dont_use_autosuspend(). If you
> enabled pm_runtime with devm_pm_runtime_enable() then it's documented
> to handle calling pm_runtime_dont_use_autosuspend() for you. See the
> kernel doc comment for devm_pm_runtime_enable(). So you can get rid of
> this.
> 

Yeah, I find the comment in the definition of 
pm_runtime_use_autosuspend() and I will remove it in the next version.

> 
>>>   err_disable_clk:
>>>        clk_disable_unprepare(dp->clock);
>>>        return ERR_PTR(ret);
> 
> Huh? Why would you call "err_disable_clk" here? The only thing that
> enables the clock is analogix_dp_resume(), right? There's something
> fishy here and it predates your patch. I suspect there were problems
> in commit f37952339cc2 ("drm/bridge: analogix_dp: handle clock via
> runtime PM"). You should fix that in a separate patch before yours.
> 

Yes, I believe there is a small bug in the commit mentioned above and I 
will add a separate patch to fix it.

> 
>>> +void analogix_dp_remove(struct analogix_dp_device *dp)
>>> +{
>>> +     if (IS_ENABLED(CONFIG_PM))
>>> +             pm_runtime_dont_use_autosuspend(dp->dev);
>>> +     else
>>> +             analogix_dp_suspend(dp);
>>> +}
>>> +EXPORT_SYMBOL_GPL(analogix_dp_remove);
> 
> See above. Proper use of "devm" should mean you don't need a remove() function.
> 

Yeah, the analogix_dp_remove() is not needed based on the above discussion.

> 

Best regards
Damon