[alsa-devel] Radeon unconnected HDMI eats samples at 280 kHz

[David Henningsson]

On 2014-09-23 16:07, Deucher, Alexander wrote:
>> -----Original Message-----
>> From: David Henningsson [mailto:david.henningsson at canonical.com]
>> Sent: Tuesday, September 23, 2014 5:48 AM
>> To: Deucher, Alexander; Takashi Iwai
>> Cc: Anssi Hannula; alsa-devel at alsa-project.org
>> Subject: Re: [alsa-devel] Radeon unconnected HDMI eats samples at 280 kHz
>>
>>
>>
>> On 2014-09-22 16:52, Deucher, Alexander wrote:
>>>> -----Original Message-----
>>>> From: David Henningsson [mailto:david.henningsson at canonical.com]
>>>> Sent: Monday, September 22, 2014 10:39 AM
>>>> To: Deucher, Alexander; Takashi Iwai
>>>> Cc: Anssi Hannula; alsa-devel at alsa-project.org
>>>> Subject: Re: [alsa-devel] Radeon unconnected HDMI eats samples at 280
>> kHz
>>>>
>>>> On 2014-09-22 14:46, Deucher, Alexander wrote:
>>>>>> -----Original Message-----
>>>>>> From: David Henningsson [mailto:david.henningsson at canonical.com]
>>>>>> Sent: Friday, September 19, 2014 8:07 PM
>>>>>> To: Deucher, Alexander; Takashi Iwai
>>>>>> Cc: Anssi Hannula; alsa-devel at alsa-project.org
>>>>>> Subject: Re: [alsa-devel] Radeon unconnected HDMI eats samples at
>> 280
>>>> kHz
>>>>>>
>>>>>> Btw, is there a register dump utility I could use to get the current
>>>>>> register value, e g by reading sysfs or procfs? It could be interesting
>>>>>> to see if anything we do on the audio side would affect this register.
>>>>>
>>>>> You can use the radeonreg tool to dump registers:
>>>>> http://cgit.freedesktop.org/~airlied/radeontool
>>>>
>>>> Thanks, I have now tried this, together with the kernel from
>>>> drm-next-3.18-wip.
>>>>
>>>>    From your patches it looks like I should look at the dumped register
>>>> 0x7300, is that correct?
>>>
>>> What GPU do you have?  The offset of that register varies between
>> generations.
>>
>> Not sure exactly what GPU info you need, but here's the lspci info:
>>
>> 01:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc.
>> [AMD/ATI] RV710 [Radeon HD 4550] [1002:9540] (prog-if 00 [VGA controller])
>>           Subsystem: PC Partner Limited / Sapphire Technology Device
>> [174b:e106]
>>
>
> That's an R7xx, so 0x7300 is correct.
>
>>>> At boot up, this register is 001000f0. (Out of curiousity, I tried
>>>> disabling unsol events from the audio side, but this did not change the
>>>> register.)
>>>> After HDMI plug in, the register changed to 0x8f1000f0, the jack
>>>> reported being plugged in, and audio worked.
>>>>
>>>> After HDMI unplugged again, the register remained at 0x8f1000f0, and
>>>> "xrandr --output HDMI-0 --off" did not help.
>>>>
>>>> However, when looking at your code, I also spotted something in the
>>>> patch called "disable audio when we disable hdmi":
>>>>
>>>> if (!enable && dig->afmt->pin) {
>>>>        r600_audio_enable(rdev, dig->afmt->pin, 0xf);
>>>>                                                ^^^
>>>> If enable is false, should we not set the last parameter to 0 instead of
>>>> 0xf?
>>>
>>> Yup.  Good catch.  I've fixed that up and pushed a new drm-next-3.18-wip
>> branch.
>>
>> Ok, I have tested this now, with mixed results. One time when I
>> unplugged I believe it correctly switched back to unplugged on the audio
>> side (after running "xrandr", with no parameters). But the next time it
>> did not.
>>
>
> Like I said, it's not tied to the physical unplug event.  You have to actually turn off the display with xrandr either explicitly or by your desktop environment as a response to a hotplug event.

But it makes sense that the audio is turned off when the video is, right?

Because if first unplug HDMI (nothing happens) and then run "xrandr" 
(without parameters), running that command causes a "re-detection" or 
whatever the correct term is - i e, my DVI screen goes black for a 
second, and afterwards the mouse pointer can no longer move to the other 
non-existent display.
At that point, audio still remains in the "plugged in" state. Also, 
executing "xrandr --output HDMI-0 --off" has no effect in that state.

>> So far, it looks like whenever the audio side reports presence, the
>> 0x7300 register is set to 0x8f1000f0. So as long as we can get the video
>> side to correctly turn off the right bits of that register when the
>> monitor is disabled/disconnected, things should be working on the audio
>> side.
>
> Can you confirm the value of 0x7300 matches what you expect in the audio driver?  E.g., does setting/clearing the appropriate bits reflect properly on the audio side?  I think the only bit that may matter is bit 31 (AUDIO_ENABLED).

I've now tried these commands:

radeonreg regset 0x7300 0x001000f0 and
radeonreg regset 0x7300 0x8f1000f0

Both commands update the audio side to report either unplugged or 
plugged in, so things seem to work as expected w r t the connection 
between this register and the audio side.


-- 
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic