HDMI hotplug enable?

Alex Deucher alexdeucher at gmail.com
Wed Jun 13 06:57:42 PDT 2012

On Wed, Jun 13, 2012 at 2:20 AM, Greg G. <dargllun at googlemail.com> wrote:
> Hi,
> [Part of this was already discussed in the thread 'OpenGL video
> performance' but I think this issue warrants a fresh discussion.]
> While researching why Alsa has issues processing the AES0 parameter to
> toggle digital audio pass-through, I realized that for being able to do
> so Alsa seems to need that mysterious /proc/asound/card*/eld#* file -
> which I don't have. Further research indicated that for that to work I
> might need working HDMI hot plug - which doesn't seem to be the case.
> Specifically, I would expect to find messages like this one in my kernel
> log:
> HDMI status: Codec=0 Pin=3 Presence_Detect=1 ELD_Valid=1
> But I don't see any of this, neither when turning my AVR off and on or
> when I physically plug/unplug the HDMI cable.
> Note that I have "drm_kms_helper poll=Y", so I do get the udev hotplug.
> But I really would like to have the "real" thing and get rid of poll=Y.

Hotplug should work fine.  The problem is the polling and hotplug
handling share the same common drm code, so I suspect disabling
polling has an adverse affect on hotplug events getting propagated to
userspace.  If you enable debugging in the drm (as root: echo 1 >
/sys/module/drm/parameters/debug), you should see some HPD messages in
your kernel log when you plug/unplug.  If you see the messages, but
don't see any userspace events, then it's probably the problem I
described above.  Note that enabling debug when X is running will
probably generate more information than is useful, so I'd suggest
enabling it when X is not running (just the radeon kernel driver

> I'm on Ubuntu 12.04 with GA-MA78GM-UD2H mainboard which has a RS780
> (HD3200) chipset. Here is a current dmesg output:
> http://paste.ubuntu.com/1030913/
> Anything I can try? Or is this already proof enough that the MB
> manufacturer has forgotten to wire up some magic hot plug pin?

Hotplug should work, and doesn't really have anything to do with hdmi
audio per se.  The gfx driver needs to get the information for the ELD
from the monitor via DDC, then pass it to the sound driver, at the
moment the radeon driver doesn't handle that.


> --
> Regards
> greg
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