linux-kernel - Re: [PATCH] lontium-lt9611: check a different register bit for HDMI sensing

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Message-ID: <YZSOzhygBRli1DVh@matsya>
Date:   Wed, 17 Nov 2021 10:40:38 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Peter Collingbourne <pcc@...gle.com>,
        Robert Foss <robert.foss@...aro.org>,
        Anibal Limon <anibal.limon@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lontium-lt9611: check a different register bit for HDMI
 sensing

Hi John,

On 16-11-21, 20:47, John Stultz wrote:
> On Tue, Nov 16, 2021 at 6:07 PM Peter Collingbourne <pcc@...gle.com> wrote:
> >
> > It has been observed that with certain monitors such as the HP Z27n,
> > the register 0x825e reads a value of 0x79 when the HDMI cable is
> > connected and 0x78 when it is disconnected, i.e. bit 0 appears
> > to correspond to the HDMI connection status and bit 2 is never
> > set. Therefore, change the driver to check bit 0 instead of bit 2.
> >
> > Signed-off-by: Peter Collingbourne <pcc@...gle.com>
> > Link: https://linux-review.googlesource.com/id/I7e76411127e1ce4988a3f6d0c8ba5f1c3d880c23
> > ---
> > N.B. I don't currently have easy access to a monitor that works
> > with the existing driver, so it would be great if people with
> > monitors that currently work could test this patch to make sure
> > that it doesn't introduce any regressions. Otherwise I will change
> > it to check both bits.
> 
> So very interesting! I gave this a spin with my monitors and it works fine.
> 
> Vinod: Can you check the datasheet to see if the wrong bit is being used here?

Well the document I have does not list this register :(

I have asked Lontium folks about this register description, will update
if I hear back. Meanwhile we can get this patch tested with different
monitors.

Thanks
-- 
~Vinod