Re: [PATCH] ALSA: hda/tegra: enable clock during probe

From: Sameer Pujar
Date: Wed Jan 30 2019 - 05:56:41 EST

On 1/30/2019 4:09 PM, Takashi Iwai wrote:
On Wed, 30 Jan 2019 10:35:35 +0100,
Jon Hunter wrote:

On 28/01/2019 06:06, Sameer Pujar wrote:
On 1/25/2019 7:34 PM, Jon Hunter wrote:
On 25/01/2019 13:58, Takashi Iwai wrote:
On Fri, 25 Jan 2019 14:26:27 +0100,
Jon Hunter wrote:
On 25/01/2019 12:40, Takashi Iwai wrote:
On Fri, 25 Jan 2019 12:36:00 +0100,
Jon Hunter wrote:
On 24/01/2019 19:08, Takashi Iwai wrote:
On Thu, 24 Jan 2019 18:36:43 +0100,
Sameer Pujar wrote:
If CONFIG_PM is disabled or runtime PM calls are forbidden, the
will not be ON. This could cause issue during probe, where hda init
setup is done. This patch checks whether runtime PM is enabled
or not.
If disabled, clocks are enabled in probe() and disabled in remove()

This patch does following minor changes as cleanup,
ÂÂ * return code check for pm_runtime_get_sync() to take care of
ÂÂÂÂ and exit gracefully.
ÂÂ * In remove path runtime PM is disabled before calling
ÂÂ * hda_tegra_disable_clocks() is moved out of CONFIG_PM_SLEEP
ÂÂ * runtime PM callbacks moved out of CONFIG_PM check

Signed-off-by: Sameer Pujar <spujar@xxxxxxxxxx>
Reviewed-by: Ravindra Lokhande <rlokhande@xxxxxxxxxx>
Reviewed-by: Jon Hunter <jonathanh@xxxxxxxxxx>
@@ -555,6 +553,13 @@ static int hda_tegra_probe(struct
platform_device *pdev)
ÂÂÂÂÂ if (!azx_has_pm_runtime(chip))
ÂÂÂÂÂÂÂÂÂ pm_runtime_forbid(hda->dev);
 + /* explicit resume if runtime PM is disabled */
+ÂÂÂ if (!pm_runtime_enabled(hda->dev)) {
+ÂÂÂÂÂÂÂ err = hda_tegra_runtime_resume(hda->dev);
+ÂÂÂÂÂÂÂ if (err)
+ÂÂÂÂÂÂÂÂÂÂÂ goto out_free;
+ÂÂÂ }
ÂÂÂÂÂ schedule_work(&hda->probe_work);
Calling runtime_resume here is really confusing...
Why? IMO it is better to have a single handler for resuming the
and so if RPM is not enabled we call the handler directly. This is
we have been advised to do in the past and do in other drivers.
See ...
The point is that we're not "resuming" anything there. It's in the
early probe stage, and the device state is uninitialized, not really
suspended. It'd end up with just calling the same helper
(hda_tegra_enable_clocks()), though.
Yes and you can make the same argument for every driver that calls
pm_runtime_get_sync() during probe to turn on clocks, handle resets,
etc, because at the end of the day the very first call to
pm_runtime_get_sync() invokes the runtime_resume callback, when we have
never been suspended.
Although there are some magical pm_runtime_*() in some places, most of
such pm_runtime_get_sync() is for the actual runtime PM management (to
prevent the runtime suspend), while the code above is for explicitly
setting up something for non-PM cases.

And if pm_runtime_get_sync() is obviously superfluous, we should
remove such calls. Really.
Yes agree.

Yes at the end of the day it is the same and given that we have done
this elsewhere I think it is good to be consistent if/where we can.
The code becomes less readable, and that's a good reason against it :)
I don't its less readable. However, I do think it is less error prone :-)
Do we have a consensus here? Request others to provide opinions to help
close on this.
I am not going to block this and ultimately it is Iwai-san call.

However, I wonder if it would be appropriate to move the whole ...

if (pm_runtime_enabled())
ret = pm_runtime_get_sync();
ret = hda_tegra_runtime_resume();

... into the probe_work function? In other words, we are just resuming
when we really need to. Unless I am still misunderstanding Iwai-san
comment. Otherwise if Iwai-san is happy with V2 then go with that.
Only from my personal taste, I find the v2 patch is better.
It like simpler, after all. That is, the code in v1 patch

probe() {
if (!pm_runtime_enabled())

work() {

becomes shorter in v2:

probe() {

work() {

However, the point about hda_tegra_remove() you raised in the v2 patch
is still valid. (BTW, I guess the discussion followed in that thread
was somehow misunderstood; your argument was about hda_tegra_remove()
while Sameer discussed about the probe.) It can be with
hda_tegra_disable_clocks() if we want more consistency.

Though, I don't mind too much about that as long as the proper comment
is given.
We might need entire functionality of hda_tegra_runtime_suspend() replicated here,
if hda_tegra_disable_clocks() were to be used. Right now it takes care of both the
cases where runtime PM is enabled/disabled. If you all agree, we can move the
discussion to v2 patch.