Re: [PATCH] drm: bridge: it66121: Fix invalid connector dereference

[Jai Luthra]

Hi Nishanth, Helen,

Thanks for the review.

On Aug 31, 2023 at 07:25:31 -0500, Nishanth Menon wrote:
> On 16:35-20230828, Helen Mae Koike Fornazier wrote:
> > On Friday, August 25, 2023 08:02 -03, Jai Luthra <j-luthra@xxxxxx> 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>
> > 
> > Reviewed-by: Helen Koike <helen.koike@xxxxxxxxxxxxx>
> 
> 
> Occurs on today's master: v6.5-8894-gb97d64c72259
> https://gist.github.com/nmenon/6c7166171729342ee0be7de90b65c5c6#file-v6-5-8894-gb97d64c72259-L821
> 
> My only complaint with the patch is - yes, it does'nt crash, but I see
> this spam on my console:
> https://gist.github.com/nmenon/6c7166171729342ee0be7de90b65c5c6#file-with-patch-on-top-L236
> 

Aradhya suggested an alternative approach [1] used by some bridges, 
where we return a buffer of 0s instead of an error here.

That will fix the spam, but more importantly will also allow playback if 
the HDMI monitor is hot-plugged later (after probe). I will send a new 
revision of this patch that uses that approach.

[1] https://lore.kernel.org/dri-devel/d2deac24-d5ab-e1c4-81c5-4874c2f5ea07@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;
> > > +	}
> > > +
> > >  	mutex_lock(&ctx->lock);
> > >  
> > >  	memcpy(buf, ctx->connector->eld,
> > > 
> > > ---
> > > base-commit: 6269320850097903b30be8f07a5c61d9f7592393
> > > change-id: 20230825-it66121_edid-6ee98517808b
> > > 
> > > Best regards,
> > > -- 
> > > Jai Luthra <j-luthra@xxxxxx>
> > >
> > 
> 
> -- 
> Regards,
> Nishanth Menon
> Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D

-- 
Thanks,
Jai

GPG Fingerprint: 4DE0 D818 E5D5 75E8 D45A AFC5 43DE 91F9 249A 7145

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