[alsa-devel] [PATCH] ALSA: hda - Enable runtime pm for Haswell

Rafael J. Wysocki rafael.j.wysocki at intel.com
Mon May 27 15:02:21 CEST 2013

On 5/23/2013 4:59 AM, Wang, Xingchao wrote:
> Hi Rafael,
>> -----Original Message-----
>> From: Wysocki, Rafael J
>> Sent: Wednesday, May 22, 2013 7:09 PM
>> To: Takashi Iwai
>> Cc: Wang, Xingchao; Girdwood, Liam R; Lin, Mengdong; Li, Jocelyn;
>> alsa-devel at alsa-project.org; Wang Xingchao
>> Subject: Re: [PATCH] ALSA: hda - Enable runtime pm for Haswell
>> On 5/22/2013 7:51 AM, Takashi Iwai wrote:
>>> At Wed, 22 May 2013 03:56:00 +0000,
>>> Wang, Xingchao wrote:
>>>> Hi,
>>>> Add Rafael in loop.
>>>>> -----Original Message-----
>>>>> From: Takashi Iwai [mailto:tiwai at suse.de]
>>>>> Sent: Thursday, May 16, 2013 4:49 PM
>>>>> To: Wang Xingchao
>>>>> Cc: Girdwood, Liam R; Lin, Mengdong; Li, Jocelyn;
>>>>> alsa-devel at alsa-project.org; Wang, Xingchao
>>>>> Subject: Re: [PATCH] ALSA: hda - Enable runtime pm for Haswell
>>>>> At Thu, 16 May 2013 16:29:05 +0800,
>>>>> Wang Xingchao wrote:
>>>>>> Haswell doesnot support runtime pm by default.
>>>>>> This patch let haswell Display HD-A controller enter runtime
>>>>>> suspend, and bring more power saving whith power-well.
>>>>>> Signed-off-by: Wang Xingchao <xingchao.wang at linux.intel.com>
>>>>> I don't think it's good to fiddle such a thing in the driver side.
>>>>> If Haswell can support runtime PM really, it should be set commonly.
>>>> I wonder whether it's HD-A driver's policy to only support runtime PM if the
>> device can support signal wakup?
>>>> According to Rafael, the device can support runtime PM regardless, no
>> matter it supports PME or not.
>>>> If so, we should remove the "if" condition check here.
>>> Well, if the decision is purely a driver issue, then we can get rid of
>>> PME check.
>> Yes, it is.
>>>     But in that case, it should be simply like:
>>> azx_probe() {
>>> 	...
>>> 	if (chip->driver_caps & AZX_DCAPS_PM_RUNTIME)
>>> 		pm_runtime_put_noidle(&pci->dev);
>>> 	...
>>> }
>>> azx_remove() {
>>> 	...
>>> 	if (chip->driver_caps & AZX_DCAPS_PM_RUNTIME)
>>> 		pm_runtime_get_noresume(&pci->dev);
>>> 	...
>>> }
>>> AFAIU, calling pm_runtime_allow() enables the runtime PM *forcibly*.
>>> Usually this isn't a good thing.
>> That's correct.  Moreover, calling both pm_runtime_allow() *and*
>> pm_runtime_put_noidle() together would be a bug IMO.
> It's interesting something maybe wrong in my test:
> 1. withtout calling pm_runtime_allow(), azx_runteim_idle/suspend() will not be called.

That's because you need to echo "auto" into the device's 
/sys/devices/.../power/control file from user space for it to work (most 
likely that's the reason).  If that file already contains "auto" when 
this happens, I'll need to look at the code to tell you what may be wrong.

> 2. another trick is on my Haswell ULT C stepping board, the runtime PM only work
> after exit from resume:
> echo mem > /sys/power/state
> if you donot let system enter suspend manually, the runtime pm will not be triggered.
> Is there any dependency between runtime pm suspend and normal suspend?

There shouldn't be any like this, and if there's one, it is a bug most 


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