Re: [PATCH] ALSA: hda: runtime PM is always active

From: Takashi Iwai <tiwai@suse.de>
To: Sameer Pujar <spujar@nvidia.com>
Cc: <abhijeet.kumar@intel.com>, <perex@perex.cz>,
	<alsa-devel@alsa-project.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ALSA: hda: runtime PM is always active
Date: Thu, 24 Jan 2019 20:12:41 +0100	[thread overview]
Message-ID: <s5h4l9xc1jq.wl-tiwai@suse.de> (raw)
In-Reply-To: <3475c359-34ce-c04b-24dc-79458b2b3e2a@nvidia.com>

On Thu, 24 Jan 2019 20:01:13 +0100,
Sameer Pujar wrote:
> 
> 
> On 1/25/2019 12:13 AM, Takashi Iwai wrote:
> > On Thu, 24 Jan 2019 19:15:12 +0100,
> > Sameer Pujar wrote:
> >>
> >> On 1/24/2019 9:34 PM, Takashi Iwai wrote:
> >>> On Thu, 24 Jan 2019 16:57:11 +0100,
> >>> Sameer Pujar wrote:
> >>>> The runtime PM count is incremented and set to active during hda codec
> >>>> device init, but it is decremented and set to suspend during exit only.
> >>>> Hence the runtime PM status is always active and hda device cannot be
> >>>> put to runtime suspend. Keeping device usage active for entire period,
> >>>> though nothing really happening on the device, seems unnecessary.
> >>>>
> >>>> This patch avoides incrementing runtime PM usage count of the device.
> >>>>
> >>>> Signed-off-by: Sameer Pujar <spujar@nvidia.com>
> >>>> Reviewed-by: Ravindra Lokhande <rlokhande@nvidia.com>
> >>>> Reviewed-by: Mohan Kumar D <mkumard@nvidia.com>
> >>> This breaks the existing things, I'm afraid.
> >>> Did you really test and verify the behavior...?
> >>>
> >>> The runtime PM refcount is decremented at snd_hda_codec_register(),
> >>> and that's the place to let runtime suspend of the codec really
> >>> effective.  (It's not about the controller, though.)
> >>>
> >> It worked fine at my end. I could put the device to runtime suspend
> >> and resume it back multiple times.
> >> Since you are suggesting it could break things, let me rework on the
> >> patch and dig up a little more to
> >> see if there is better way to fix this.
> > Well, I don't see what you want to "fix".  Do you see any bug?
> I was expecting the device to be runtime suspended, once probe is
> finished, until I playback something on it.
> But it appears that rutntime PM is always active and runtime PM
> suspend callback never happens.

Does the behavior really appear?  If so, it's a bug.

The current design is to enable the runtime PM *after* the device
registration.  Otherwise it makes no sense -- the problem doesn't
finish yet before that point.

thanks,

Takashi