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

[Anssi Hannula]

17.09.2014, 16:40, David Henningsson kirjoitti:
> Hi,

Hi,

> While investigating some interesting debug output from PulseAudio, I 
> tried to figure out the cause.
> 
>  From what I can tell, my Radeon seems to ask for new samples at a very 
> high rate, which I estimate to be around 280 kHz. My radeon card has 
> DVI, HDMI and VGA connectors, and the only thing connected is my screen 
> over DVI.
> 
> I'm currently running the 3.13 kernel with updated hda directory from 
> Takashi's tree, but I think it's been this way for a long time.
> 
> Note that if a screen is connected to the HDMI card, the problem 
> disappears and sample rates are normal.
> In short, do you think this is a driver bug, or just something we have 
> to live with as some sort of hw anomaly?
> Since nothing is connected, it does not really hurt, except PulseAudio 
> gets confused (in a way that could potentially cause problems for 
> low-latency output, should something be connected later on).

Not sure.
IIRC, unlike the other gpus, on radeon the video driver needs to
"manually" set sample rate dividers/etc based on the pixel clock rate,
so I guess this might mean we can't have a proper audio clock without
enabled video...

Alex, any thoughts/info?


If this is the case, it would probably be best if we prevented opening
the device when output is not active (unless this causes some other
issues), but I guess there is currently no easy way for the _audio_
driver to know that...


> For reference, here's lspci of the HDMI card:
> 
> 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]
> 01:00.1 Audio device [0403]: Advanced Micro Devices, Inc. [AMD/ATI] 
> RV710/730 HDMI Audio [Radeon HD 4000 series] [1002:aa38]
> 	Subsystem: PC Partner Limited / Sapphire Technology Device [174b:aa38]
> 
> 


-- 
Anssi Hannula