Hi Aradhya,
Thanks for the comments.
On Aug 28, 2023 at 16:34:30 +0530, Aradhya Bhatia wrote:
> Hi Jai,
>
> Thanks for debugging the issue.
>
> On 25-Aug-23 16:32, Jai Luthra wrote:
> > Fix the NULL pointer dereference when no monitor is connected, and the
> > sound card is opened from userspace.
> >
> > Instead return an error as EDID information cannot be provided to
> > the sound framework if there is no connector attached.
> >
> > Fixes: e0fd83dbe924 ("drm: bridge: it66121: Add audio support")
> > Reported-by: Nishanth Menon <nm@xxxxxx>
> > Closes: https://lore.kernel.org/all/20230825105849.crhon42qndxqif4i@gondola/
> > Signed-off-by: Jai Luthra <j-luthra@xxxxxx>
> > ---
> > drivers/gpu/drm/bridge/ite-it66121.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/bridge/ite-it66121.c b/drivers/gpu/drm/bridge/ite-it66121.c
> > index 466641c77fe9..d6fa00dea464 100644
> > --- a/drivers/gpu/drm/bridge/ite-it66121.c
> > +++ b/drivers/gpu/drm/bridge/ite-it66121.c
> > @@ -1446,6 +1446,11 @@ static int it66121_audio_get_eld(struct device *dev, void *data,
> > {
> > struct it66121_ctx *ctx = dev_get_drvdata(dev);
> >
> > + if (!ctx->connector) {
> > + dev_dbg(dev, "No connector present, cannot provide EDID data");
> > + return -EINVAL;
> > + }
> > +
>
> There are not many HDMI bridges that support codecs in the kernel, but
> upon a quick look, bridge/analogix/anx7625.c and
> bridge/synopsys/dw-hdmi* gracefully return a buffer of 0s when the
> connector is unavailable.
Interesting, that sounds cleaner to me.
>
> I am not sure why that is done, but I also don't see the hdmi-codec
> driver handle the 0s situation properly. It is business as usual for the
> hdmi-codec.
Chasing this down through the hdmi-codec driver and sound framework, it
will use sane defaults for supported channels and sample rates if the
actual EDID struct we are passing is all 0s. I tested it out on the
beagle play board and did not see any crashes.
>
> Did you come across some observation when you were testing?
Yes, with the current state of the patch, if I plug-in a monitor after
the soundcard is probed I cannot playback audio, because we returned an
error initially.
This issue goes away if we return a buffer of 0s like those other
bridges. Overall I'm happy with this idea, so I will send a v2 fixing
this.
>
> Regards
> Aradhya
>
> > mutex_lock(&ctx->lock);
> >
> > memcpy(buf, ctx->connector->eld,
> >
> > ---
> > base-commit: 6269320850097903b30be8f07a5c61d9f7592393
> > change-id: 20230825-it66121_edid-6ee98517808b
> >
> > Best regards,
>
--
Thanks,
Jai
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