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Subject: Re: [PATCH 2/2] ALSA: hda: Allow HDA to be runtime suspended when
 dGPU is not bound
From:   Kai-Heng Feng <kai.heng.feng@canonical.com>
In-Reply-To: <20190827223125.GB9987@google.com>
Date:   Wed, 28 Aug 2019 16:25:08 +0800
Cc:     tiwai@suse.com, linux-pci@vger.kernel.org,
        alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org
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Message-Id: <66C43B81-0A08-437F-B099-1C757A42E912@canonical.com>
References: <20190827134756.10807-1-kai.heng.feng@canonical.com>
 <20190827134756.10807-2-kai.heng.feng@canonical.com>
 <20190827223125.GB9987@google.com>
To:     Bjorn Helgaas <helgaas@kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
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Hi Bjorn,

at 06:31, Bjorn Helgaas <helgaas@kernel.org> wrote:

> On Tue, Aug 27, 2019 at 09:47:56PM +0800, Kai-Heng Feng wrote:
>> It's a common practice to let dGPU unbound and use PCI port PM to
>> disable its power through _PR3. When the dGPU comes with an HDA
>> function, the HDA won't be suspended if the dGPU is unbound, so the dGPU
>> power can't be disabled.
>
> Just a terminology question:
>
> I thought "using PCI port PM" meant using the PCI Power Management
> Capability in config space to directly change the device's power
> state, e.g., in pci_raw_set_power_state().

What I meant is to use pcieport.ko directly.

>
> And I thought using _PS3, _PR3, etc would be part of "platform power
> management”?

Ok, will update the wording.

>
> And AFAICT, _PR3 merely returns a list of power resources; it doesn't
> disable power itself.

Yes, through its _PS3 and _OFF. I’ll update the wording.

Kai-Heng

>
>> Commit 37a3a98ef601 ("ALSA: hda - Enable runtime PM only for
>> discrete GPU") only allows HDA to be runtime-suspended once GPU is
>> bound, to keep APU's HDA working.
>>
>> However, HDA on dGPU isn't that useful if dGPU is unbound. So let relax
>> the runtime suspend requirement for dGPU's HDA function, to save lots of
>> power.
>>
>> BugLink: https://bugs.launchpad.net/bugs/1840835
>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
>> ---
>>  sound/pci/hda/hda_intel.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
>> index 99fc0917339b..d4ee070e1a29 100644
>> --- a/sound/pci/hda/hda_intel.c
>> +++ b/sound/pci/hda/hda_intel.c
>> @@ -1285,7 +1285,8 @@ static void init_vga_switcheroo(struct azx *chip)
>>  		dev_info(chip->card->dev,
>>  			 "Handle vga_switcheroo audio client\n");
>>  		hda->use_vga_switcheroo = 1;
>> -		hda->need_eld_notify_link = 1; /* cleared in gpu_bound op */
>> +		/* cleared in gpu_bound op */
>> +		hda->need_eld_notify_link = !pci_pr3_present(p);
>>  		chip->driver_caps |= AZX_DCAPS_PM_RUNTIME;
>>  		pci_dev_put(p);
>>  	}
>> -- 
>> 2.17.1