Possible fix for snd-hda-intel model=no-jd failing since ~linux-3.9-rc1

[adam richter <adamrichter4@xxxxxxxxx>]

Hi.

Please feel free to redirect me to another email address.  I did not
notice any contact information for sound/pci/hda in
linux-3.16-rc4/MAINATINERS.

The "model=no-jd" argument has not initialized correctly for me for
linux-3.9-rc1 (if I recall correctly) through linux-3.16-rc4, although
I have not tried every release candidate in between.

The symptom is that, on a computer with an analog audio output jack
that usually does not correctly sense a device is plugged in, audio
output is completely muted until I physically replug the cable, even
though I specified "model=no-jd" as an argument to the snd-hda-intel
kernel module, which is supposed to cause the kernel to ignore the
jack sense reported by hardware and just drive the audio output even
if the hardware jack sense indicates nothing is plugged in.

I have found a few single line workarounds that work, of which my
favorite is the following (also attached to this email, in case any
mailer subjects this message to reformatting), because it does not add
code to anything that gets called frequently.

--- linux-3.16.0-rc4-64bit/sound/pci/hda/hda_jack.c.orig    2014-07-08 15:34
:36.567535340 -0700
+++ linux-3.16.0-rc4-64bit/sound/
pci/hda/hda_jack.c    2014-07-08 15:35:05.1715
34923 -0700
@@ -106,6 +106,7 @@ snd_hda_jack_tbl_new(struct hda_codec *c
    jack->nid = nid;
    jack->jack_dirty = 1;
    jack->tag = codec->jacktbl.used;
+    jack->phantom_jack = codec->no_jack_detect;
    return jack;
}
EXPORT_SYMBOL_GPL(snd_hda_jack_tbl_new);


Signed-off-by: Adam J. Richter <adam_richter2004@xxxxxxxxx>


I consider this a workaround rather than than a perfect fix, because I
think the underlying problem seems to be some kind of initialization
order issue that I don't fully understand.  Basically, by the time
jack->phantom_jack was being set, some caller had already called
jack_detect_update(), which loaded the incorrect jack sense result
from hardware and cleared jack->jack_dirty, so the jack sense would
not be set again.  At least that is what I think the underlying
problem probably is.

Also, if a change like this is to be integrated, I'd like to know if
it might be better for the line that I added to be:

          jack->phantom_jack = !is_jack_detectable(codec, nid);

...which is what add_jack_kctl does (not sure why add_jack_kctls does
not, by the way, at the risk of making a spectacle of my ignorance).
My doubt about this approach is that perhaps is_jack_detectable()
relies on some initialization that has not occurred at that point.

Anyhow, I'd like to get the process started of either pushing this
change upstream or quickly developing a more correct fix.  If a more
correct fix does not become apparent in the next few days, I would
recommend pushing the workaround upstream now until some future code
cleanup, so people will no longer be effected by the bug.

Any technical input or advice on how to proceed is welcome.  Thanks
for taking the time to consider this.

Adam Richter

--- linux-3.16.0-rc4-64bit/sound/pci/hda/hda_jack.c.orig	2014-07-08 15:34:36.567535340 -0700
+++ linux-3.16.0-rc4-64bit/sound/pci/hda/hda_jack.c	2014-07-08 15:35:05.171534923 -0700
@@ -106,6 +106,7 @@ snd_hda_jack_tbl_new(struct hda_codec *c
 	jack->nid = nid;
 	jack->jack_dirty = 1;
 	jack->tag = codec->jacktbl.used;
+	jack->phantom_jack = codec->no_jack_detect;
 	return jack;
 }
 EXPORT_SYMBOL_GPL(snd_hda_jack_tbl_new);