Re: [PATCH 2/2] ALSA: hda: Allow HDA to be runtime suspended when dGPU is not bound

Kai-Heng Feng
2019-08-28T08:25:18Z

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