Message-ID: <CAD=FV=Ubi11ejFO8asRF57OYGb3fGEFo0mz_04-5yQ89PPw3_A@mail.gmail.com>
Date: Thu, 23 Jan 2025 19:13:57 -0800
From: Doug Anderson <dianders@...omium.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Damon Ding <damon.ding@...k-chips.com>, heiko@...ech.de, robh@...nel.org, 
	krzk+dt@...nel.org, conor+dt@...nel.org, rfoss@...nel.org, vkoul@...nel.org, 
	sebastian.reichel@...labora.com, cristian.ciocaltea@...labora.com, 
	l.stach@...gutronix.de, andy.yan@...k-chips.com, hjc@...k-chips.com, 
	algea.cao@...k-chips.com, kever.yang@...k-chips.com, 
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-phy@...ts.infradead.org
Subject: Re: [PATCH v6 07/14] drm/bridge: analogix_dp: Add support to get
 panel from the DP AUX bus

Hi,

On Thu, Jan 23, 2025 at 3:25 AM Dmitry Baryshkov
<dmitry.baryshkov@...aro.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


> > 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@...k-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.


> > +     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.


> > +     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.


> > +             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.


> > +     }
> > +
> >       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.


> >  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.


> > +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.

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