Re: 答复: [PATCH] vgaswitchroo: set audio client id according to bound gpu client id

[Alex Deucher]

On Mon, Jul 9, 2018 at 6:16 AM, Qu, Jim <Jim.Qu at amd.com> wrote:
> Hi Lukas,
>
> Thanks to your explanation, and see comments in line.
>
>
> Do you need to runtime resume the HDA controller even if user space isn't
> streaming audio?  Why, and in which situation exactly?
>
> Jim: OEM system uses pactl to queiry audio card and audio output sink, since the audio has power down by runtime pm, so the audio card and output sink are all unavailable. they could not select the available HDMI audio for audio playing.
>
> You're saying above that the HDA controller isn't runtime resumed on
> hotplug of a display.  Is that necessary to retrieve ELD or something?
> I'm not sure if there's code in the HDA driver to acquire a runtime PM
> ref on HPD, but maybe it's necessary.  Or maybe the code is there but
> somehow no HPD interrupt is received by the HDA driver?
>
> Jim: So far, I do not find any code about audio response HPD in kernel. the HPD interrupt will sent to user mode via uevent, not sure whether audio user mode driver can receive the event or not.

On the gfx side at least, we can get a hotplug event via ACPI
(depending on the OEM design) if displays are attached/detached while
the dGPU is powered down.  I suppose the gfx driver could call into
the audio driver during one of those events.  On the gfx side at least
we just generate the gfx hotplug event and let userspace deal with it.

Alex

>
> Thanks
> JimQu
>
> ________________________________________
> 发件人: Lukas Wunner <lukas at wunner.de>
> 发送时间: 2018年7月9日 17:27
> 收件人: Qu, Jim
> 抄送: alsa-devel at alsa-project.org; dri-devel at lists.freedesktop.org; Deucher, Alexander; amd-gfx at lists.freedesktop.org
> 主题: Re: [PATCH] vgaswitchroo: set audio client id according to bound gpu client id
>
> On Mon, Jul 09, 2018 at 08:52:33AM +0000, Qu, Jim wrote:
>> Now, I found the audio device will auto suspend even if the gpu is active,
>> and if I plug in a HDMI device it also do not resume back.
>>
>> 1. Did you encounter similar issue before?
>> 2. audio will auto suspend as default at beginning of boot, is it expect
>> behaviour?
>
> Yes, that's expected.  Once you start streaming audio to attached displays,
> user space opens the codec device and this causes the HDA controller to
> runtime resume.  If the discrete GPU is suspended at that moment, it will
> be powered on and kept powered on as long as user space is streaming audio.
>
> Do you need to runtime resume the HDA controller even if user space isn't
> streaming audio?  Why, and in which situation exactly?
>
> You're saying above that the HDA controller isn't runtime resumed on
> hotplug of a display.  Is that necessary to retrieve ELD or something?
> I'm not sure if there's code in the HDA driver to acquire a runtime PM
> ref on HPD, but maybe it's necessary.  Or maybe the code is there but
> somehow no HPD interrupt is received by the HDA driver?
>
> Thanks,
>
> Lukas
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