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

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Message-ID: <ljopjy4gjuduyjq6auhwi3jinblqagf6vghgvw3edfmj6tyerw@q2kglcng3glf>
Date:   Fri, 1 Sep 2023 14:36:27 +0530
From:   Jai Luthra <j-luthra@...com>
To:     Nishanth Menon <nm@...com>,
        Helen Mae Koike Fornazier <helen.koike@...labora.com>
CC:     Phong LE <ple@...libre.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Nicolas Belin <nbelin@...libre.com>,
        "Andy.Hsieh" <Andy.Hsieh@...iatek.com>,
        Aradhya Bhatia <a-bhatia1@...com>, <devarsht@...com>,
        <linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] drm: bridge: it66121: Fix invalid connector dereference

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@...com> 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@...com>
> > > Closes: https://lore.kernel.org/all/20230825105849.crhon42qndxqif4i@gondola/
> > > Signed-off-by: Jai Luthra <j-luthra@...com>
> > 
> > Reviewed-by: Helen Koike <helen.koike@...labora.com>
> 
> 
> 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@ti.com/

> 
> > 
> > > ---
> > >  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@...com>
> > >
> > 
> 
> -- 
> 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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