[alsa-devel] [PATCH 0/3] Make HDMI ELD usable with hotplug

[David Henningsson]

On 02/18/2013 11:39 PM, Ville Syrjälä wrote:
> On Mon, Feb 18, 2013 at 02:50:49PM +0100, David Henningsson wrote:
>> On 02/18/2013 02:35 PM, Takashi Iwai wrote:
>>> At Mon, 18 Feb 2013 14:11:10 +0100,
>>> David Henningsson wrote:
>>>>
>>>> I'm experimenting with using ELD information in PulseAudio and found
>>>> that it didn't work very well with hotplugging.
>>>> Neither the proc file nor the ELD kcontrol was cleared correctly after
>>>> unplug, and there was no way (except polling) to find out when ELD
>>>> has become available.
>>>
>>> Did you try Xingchao's patch for drm/i915?  It's queued in
>>> drm-intel-next:
>>>
>>>       commit 7b9f35a6dd72f89452c58bbdbaf063027bf857ec
>>>       Author: Wang Xingchao <xingchao.wang at intel.com>
>>>       Date:   Tue Jan 22 23:25:25 2013 +0800
>>>
>>>       drm/i915: HDMI/DP - ELD info refresh support for Haswell
>>
>> Thanks for the hint. I'm currently developing not on a Haswell machine,
>> but an (I think) Arrandale that I bought a few years ago. So I guess
>> this patch does not have any effect on my hw?
>
> While reviewing that patch I asked whether we need something like that
> on other platforms. Unfortunately I didn't get a real answer. The logic
> in the patch would seem to apply equally to all platforms, not just HSW.
> We also seem to be doing silly things like flipping the ELD valid bit
> in the register on and off a few times when we update the ELD. But I'm
> not all that familiar with the topic so take my ramblings with a pinch
> of salt.
>
> But in any case, if you're seeing a problem with the behaviour of i915
> you should definitely report it.

Looking at the HDA spec [1], e g "Figure 72: PD and ELDV unsolicited 
responses flow for digital display codecs" it looks like it's not valid 
to first send the PD bit and then ELDV a while later. So then I guess 
it's an issue that this actually seem to happen on the machine I use for 
testing this code.

 From the same figure, it also looks like ELDV can be flipped back and 
forth (due to mode changes) when PD is true; so making patches that deal 
with PD and ELDV independently seem to be the right thing nonetheless.


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

[1] 
http://www.intel.com/content/www/us/en/standards/high-definition-audio-specification.html