[PATCH] drm/bridge: ti-sn65dsi86: Properly undo autosuspend

[PATCH] drm/bridge: ti-sn65dsi86: Properly undo autosuspend

[Douglas Anderson]

The PM Runtime docs say:
  Drivers in ->remove() callback should undo the runtime PM changes done
  in ->probe(). Usually this means calling pm_runtime_disable(),
  pm_runtime_dont_use_autosuspend() etc.

We weren't doing that for autosuspend. Let's do it.

Fixes: 9bede63127c6 ("drm/bridge: ti-sn65dsi86: Use pm_runtime autosuspend")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 38616aab12ac..fb6c588b0f71 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -1758,6 +1758,7 @@ static inline void ti_sn_gpio_unregister(void) {}
 
 static void ti_sn65dsi86_runtime_disable(void *data)
 {
+	pm_runtime_dont_use_autosuspend(data);
 	pm_runtime_disable(data);
 }
 
@@ -1817,11 +1818,11 @@ static int ti_sn65dsi86_probe(struct i2c_client *client,
 				     "failed to get reference clock\n");
 
 	pm_runtime_enable(dev);
+	pm_runtime_set_autosuspend_delay(pdata->dev, 500);
+	pm_runtime_use_autosuspend(pdata->dev);
 	ret = devm_add_action_or_reset(dev, ti_sn65dsi86_runtime_disable, dev);
 	if (ret)
 		return ret;
-	pm_runtime_set_autosuspend_delay(pdata->dev, 500);
-	pm_runtime_use_autosuspend(pdata->dev);
 
 	ti_sn65dsi86_debugfs_init(pdata);
 
-- 
2.35.1.473.g83b2b277ed-goog

Re: [PATCH] drm/bridge: ti-sn65dsi86: Properly undo autosuspend

[Linus Walleij]

On Tue, Feb 22, 2022 at 11:19 PM Douglas Anderson <dianders@chromium.org> wrote:
>
> The PM Runtime docs say:
>   Drivers in ->remove() callback should undo the runtime PM changes done
>   in ->probe(). Usually this means calling pm_runtime_disable(),
>   pm_runtime_dont_use_autosuspend() etc.
>
> We weren't doing that for autosuspend. Let's do it.
>
> Fixes: 9bede63127c6 ("drm/bridge: ti-sn65dsi86: Use pm_runtime autosuspend")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

Hm. I know a few places in drivers where I don't do this :/
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

Re: [PATCH] drm/bridge: ti-sn65dsi86: Properly undo autosuspend

[Laurent Pinchart]

On Tue, Feb 22, 2022 at 11:44:54PM +0100, Linus Walleij wrote:
> On Tue, Feb 22, 2022 at 11:19 PM Douglas Anderson <dianders@chromium.org> wrote:
> >
> > The PM Runtime docs say:
> >   Drivers in ->remove() callback should undo the runtime PM changes done
> >   in ->probe(). Usually this means calling pm_runtime_disable(),
> >   pm_runtime_dont_use_autosuspend() etc.
> >
> > We weren't doing that for autosuspend. Let's do it.
> >
> > Fixes: 9bede63127c6 ("drm/bridge: ti-sn65dsi86: Use pm_runtime autosuspend")
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> 
> Hm. I know a few places in drivers where I don't do this :/

It seems to be a very common problem indeed, I haven't seen any driver
yet that uses pm_runtime_dont_use_autosuspend(). We could play a game of
whack-a-mole, but we'll never win. Could this be solved in the runtime
PM framework instead ? pm_runtime_disable() could disable auto-suspend.
If there are legitimate use cases for disabling runtime PM temporarily
without disabling auto-suspend, then a new function designed
specifically for remove() that would take care of cleaning everything up
could be another option.

> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

-- 
Regards,

Laurent Pinchart

Re: [PATCH] drm/bridge: ti-sn65dsi86: Properly undo autosuspend

[Doug Anderson]

Hi,

On Tue, Feb 22, 2022 at 9:08 PM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> On Tue, Feb 22, 2022 at 11:44:54PM +0100, Linus Walleij wrote:
> > On Tue, Feb 22, 2022 at 11:19 PM Douglas Anderson <dianders@chromium.org> wrote:
> > >
> > > The PM Runtime docs say:
> > >   Drivers in ->remove() callback should undo the runtime PM changes done
> > >   in ->probe(). Usually this means calling pm_runtime_disable(),
> > >   pm_runtime_dont_use_autosuspend() etc.
> > >
> > > We weren't doing that for autosuspend. Let's do it.
> > >
> > > Fixes: 9bede63127c6 ("drm/bridge: ti-sn65dsi86: Use pm_runtime autosuspend")
> > > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> >
> > Hm. I know a few places in drivers where I don't do this :/
>
> It seems to be a very common problem indeed, I haven't seen any driver
> yet that uses pm_runtime_dont_use_autosuspend(). We could play a game of
> whack-a-mole, but we'll never win. Could this be solved in the runtime
> PM framework instead ? pm_runtime_disable() could disable auto-suspend.
> If there are legitimate use cases for disabling runtime PM temporarily
> without disabling auto-suspend, then a new function designed
> specifically for remove() that would take care of cleaning everything up
> could be another option.

Yeah, it would be good. It's probably not a yak I have time to shave
right now, though. :(

I _suspect_ that there are legitimate reasons we can't just magically
do it in pm_runtime_disable(). If nothing else I believe there are
legitimate code paths during normal operation that look like this:

  pm_runtime_disable();
  do_something_that_needs_pm_runtime_disabled();
  pm_runtime_enable();

Also: if it were really a simple problem to solve one would have
thought that it would have been solved initially instead of adding
documentation particularly mentioning
pm_runtime_dont_use_autosuspend()

How about a middle ground, though: we could add a devm function that
does all the magic. Somewhat recently devm_pm_runtime_enable() was
added. What if we add a variant for those that use autosuspend, like:

devm_pm_runtime_enable_with_autosuspend(dev, initial_delay)

That would:
* pm_runtime_enable()
* pm_runtime_set_autosuspend_delay()
* pm_runtime_use_autosuspend()
* Use devm_add_action_or_reset() to undo everything.

Assuming that the pm_runtime folks are OK with that, we could
transition things over to the new function once it rolls into
mainline.

So this doesn't magically fix all existing code but provides a path to
make this more discoverable.

-Doug

Re: [PATCH] drm/bridge: ti-sn65dsi86: Properly undo autosuspend

[Laurent Pinchart]

Hi Doug,

On Wed, Feb 23, 2022 at 07:43:27AM -0800, Doug Anderson wrote:
> On Tue, Feb 22, 2022 at 9:08 PM Laurent Pinchart wrote:
> > On Tue, Feb 22, 2022 at 11:44:54PM +0100, Linus Walleij wrote:
> > > On Tue, Feb 22, 2022 at 11:19 PM Douglas Anderson wrote:
> > > >
> > > > The PM Runtime docs say:
> > > >   Drivers in ->remove() callback should undo the runtime PM changes done
> > > >   in ->probe(). Usually this means calling pm_runtime_disable(),
> > > >   pm_runtime_dont_use_autosuspend() etc.
> > > >
> > > > We weren't doing that for autosuspend. Let's do it.
> > > >
> > > > Fixes: 9bede63127c6 ("drm/bridge: ti-sn65dsi86: Use pm_runtime autosuspend")
> > > > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > >
> > > Hm. I know a few places in drivers where I don't do this :/
> >
> > It seems to be a very common problem indeed, I haven't seen any driver
> > yet that uses pm_runtime_dont_use_autosuspend(). We could play a game of
> > whack-a-mole, but we'll never win. Could this be solved in the runtime
> > PM framework instead ? pm_runtime_disable() could disable auto-suspend.
> > If there are legitimate use cases for disabling runtime PM temporarily
> > without disabling auto-suspend, then a new function designed
> > specifically for remove() that would take care of cleaning everything up
> > could be another option.
> 
> Yeah, it would be good. It's probably not a yak I have time to shave
> right now, though. :(

I don't insist on shaving that yak right now :-) This patch is fine.

> I _suspect_ that there are legitimate reasons we can't just magically
> do it in pm_runtime_disable(). If nothing else I believe there are
> legitimate code paths during normal operation that look like this:
> 
>   pm_runtime_disable();
>   do_something_that_needs_pm_runtime_disabled();
>   pm_runtime_enable();
> 
> Also: if it were really a simple problem to solve one would have
> thought that it would have been solved initially instead of adding
> documentation particularly mentioning
> pm_runtime_dont_use_autosuspend()

I'm not sure, look at how long it took for us to get
pm_runtime_resume_and_get(). The problem has been considered for years
as a non-issue by the runtime PM developers. It feels like the API is
developed without considering its users.

> How about a middle ground, though: we could add a devm function that
> does all the magic. Somewhat recently devm_pm_runtime_enable() was
> added. What if we add a variant for those that use autosuspend, like:
> 
> devm_pm_runtime_enable_with_autosuspend(dev, initial_delay)
> 
> That would:
> * pm_runtime_enable()
> * pm_runtime_set_autosuspend_delay()
> * pm_runtime_use_autosuspend()
> * Use devm_add_action_or_reset() to undo everything.
> 
> Assuming that the pm_runtime folks are OK with that, we could
> transition things over to the new function once it rolls into
> mainline.
> 
> So this doesn't magically fix all existing code but provides a path to
> make this more discoverable.

Sounds like a good idea. I wonder if this could be handled by
devm_pm_runtime_enable() actually. If a driver calls
devm_pm_runtime_enable() and then enables auto-suspend, can't the
runtime PM core reasonably expect that auto-suspend should be disabled
at .remove() time ? The pm_runtime_disable_action() function could
disable auto-suspend unconditionally (assuming
pm_runtime_use_autosuspend() and pm_runtime_dont_use_autosuspend() don't
need to be balanced, if they do, then I'll just go cry in a corner).

-- 
Regards,

Laurent Pinchart

Re: [PATCH] drm/bridge: ti-sn65dsi86: Properly undo autosuspend

[Doug Anderson]

Hi,

On Wed, Feb 23, 2022 at 7:55 AM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> > How about a middle ground, though: we could add a devm function that
> > does all the magic. Somewhat recently devm_pm_runtime_enable() was
> > added. What if we add a variant for those that use autosuspend, like:
> >
> > devm_pm_runtime_enable_with_autosuspend(dev, initial_delay)
> >
> > That would:
> > * pm_runtime_enable()
> > * pm_runtime_set_autosuspend_delay()
> > * pm_runtime_use_autosuspend()
> > * Use devm_add_action_or_reset() to undo everything.
> >
> > Assuming that the pm_runtime folks are OK with that, we could
> > transition things over to the new function once it rolls into
> > mainline.
> >
> > So this doesn't magically fix all existing code but provides a path to
> > make this more discoverable.
>
> Sounds like a good idea. I wonder if this could be handled by
> devm_pm_runtime_enable() actually. If a driver calls
> devm_pm_runtime_enable() and then enables auto-suspend, can't the
> runtime PM core reasonably expect that auto-suspend should be disabled
> at .remove() time ? The pm_runtime_disable_action() function could
> disable auto-suspend unconditionally (assuming
> pm_runtime_use_autosuspend() and pm_runtime_dont_use_autosuspend() don't
> need to be balanced, if they do, then I'll just go cry in a corner).

I like your idea. I think you're right that we can just leverage the
existing function. This yak didn't look to hairy, so I posted a patch:

https://lore.kernel.org/r/20220223083441.1.I925ce9fa12992a58caed6b297e0171d214866fe7@changeid

I guess now we see what Rafael thinks. ;-)

-Doug

Re: [PATCH] drm/bridge: ti-sn65dsi86: Properly undo autosuspend

[Doug Anderson]

Hi,

On Wed, Feb 23, 2022 at 7:55 AM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Doug,
>
> On Wed, Feb 23, 2022 at 07:43:27AM -0800, Doug Anderson wrote:
> > On Tue, Feb 22, 2022 at 9:08 PM Laurent Pinchart wrote:
> > > On Tue, Feb 22, 2022 at 11:44:54PM +0100, Linus Walleij wrote:
> > > > On Tue, Feb 22, 2022 at 11:19 PM Douglas Anderson wrote:
> > > > >
> > > > > The PM Runtime docs say:
> > > > >   Drivers in ->remove() callback should undo the runtime PM changes done
> > > > >   in ->probe(). Usually this means calling pm_runtime_disable(),
> > > > >   pm_runtime_dont_use_autosuspend() etc.
> > > > >
> > > > > We weren't doing that for autosuspend. Let's do it.
> > > > >
> > > > > Fixes: 9bede63127c6 ("drm/bridge: ti-sn65dsi86: Use pm_runtime autosuspend")
> > > > > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > > >
> > > > Hm. I know a few places in drivers where I don't do this :/
> > >
> > > It seems to be a very common problem indeed, I haven't seen any driver
> > > yet that uses pm_runtime_dont_use_autosuspend(). We could play a game of
> > > whack-a-mole, but we'll never win. Could this be solved in the runtime
> > > PM framework instead ? pm_runtime_disable() could disable auto-suspend.
> > > If there are legitimate use cases for disabling runtime PM temporarily
> > > without disabling auto-suspend, then a new function designed
> > > specifically for remove() that would take care of cleaning everything up
> > > could be another option.
> >
> > Yeah, it would be good. It's probably not a yak I have time to shave
> > right now, though. :(
>
> I don't insist on shaving that yak right now :-) This patch is fine.

Landed in drm-misc-fixes:

26d347434829 drm/bridge: ti-sn65dsi86: Properly undo autosuspend

-Doug