[PATCH] ALSA: hda: enable the runtime_pm for non-vgaswitcheroo hda controllers

[Roy Spliet]

Dear Hui, Takashi,

Op 14-04-2020 om 13:35 schreef Hui Wang:
> 
> On 2020/4/14 下午6:27, Takashi Iwai wrote:
>> On Tue, 14 Apr 2020 12:14:05 +0200,
>> Hui Wang wrote:
>>> Before the pci_driver->probe() is called, the pci subsystem calls
>>> runtime_forbib() and runtime_get_sync() on this pci dev, so only call
>>> runtime_put_autosuspend() is not enough to enable the runtime_pm on
>>> this device.
>>>
>>> For controllers with vgaswitcheroo feature, the pci/quirks.c will call
>>> runtime_allow() for this dev, then the controllers could enter
>>> rt_idle/suspend/resume, but for non-vgaswitcheroo controllers like
>>> Intel hda controllers, the runtime_pm is not enabled even it calls
>>> put_autosuspend(). Need to call runtime_allow() for those controllers
>>> in the hda driver.

 From what I can tell there are no ill effects of calling 
runtime_allow() twice. Technically, the check against 
use_vga_switcheroo() is thus redundant.
Is there a good reason why runtime_allow() is called in the pci quirks 
rather than in hda_intel? Is it a suggestion to perform this call in 
hda_intel regardless of whether it's a switcheroo-device or not, and 
removing calls to runtime_allow() from the PCI quirks?
Thanks. Best,

Roy
>>>
>>> Signed-off-by: Hui Wang <hui.wang at canonical.com>
>> Was this behavior changed from the earlier kernels?  I thought this
>> was left untouched because it's supposed to be set via udev rules or
>> such.
> 
> Oh, I don't know that,  according to my test with ubuntu rootfs, the 
> runtime pm is not enabled on Intel's hda controllers. But with the sof 
> driver, the controller driver calls runtime_allow() 
> (soc/sof/sof-pci-dev.c), so I sent this patch.
> 
> Regards,
> 
> Hui.
> 
>> OTOH, enabling the runtime PM is almost mandatory for modern systems,
>> and I'm fine to apply this kind of forcible enablement.
>>
>>
>> thanks,
>>
>> Takashi
>>
>>
>>> ---
>>>   sound/pci/hda/hda_intel.c | 2 ++
>>>   1 file changed, 2 insertions(+)
>>>
>>> diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
>>> index 8519051a426e..779705bef88b 100644
>>> --- a/sound/pci/hda/hda_intel.c
>>> +++ b/sound/pci/hda/hda_intel.c
>>> @@ -2356,6 +2356,8 @@ static int azx_probe_continue(struct azx *chip)
>>>       if (azx_has_pm_runtime(chip)) {
>>>           pm_runtime_use_autosuspend(&pci->dev);
>>> +        if (!use_vga_switcheroo(chip))
>>> +            pm_runtime_allow(&pci->dev);
>>>           pm_runtime_put_autosuspend(&pci->dev);
>>>       }
>>> -- 
>>> 2.17.1
>>>