linux-kernel - Re: [PATCH 2/2] drm/bridge: lt9611: Use both bits for HDMI sensing

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Date:   Mon, 23 May 2022 12:18:57 +0200
From:   Robert Foss <robert.foss@...aro.org>
To:     John Stultz <jstultz@...gle.com>
Cc:     linux-kernel@...r.kernel.org, Yongqin Liu <yongqin.liu@...aro.org>,
        Amit Pundir <amit.pundir@...aro.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Vinod Koul <vkoul@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        kernel-team@...roid.com
Subject: Re: [PATCH 2/2] drm/bridge: lt9611: Use both bits for HDMI sensing

On Wed, 11 May 2022 at 03:26, John Stultz <jstultz@...gle.com> wrote:
>
> In commit 19cf41b64e3b ("lontium-lt9611: check a different
> register bit for HDMI sensing"), the bit flag used to detect
> HDMI cable connect was switched from BIT(2) to BIT(0) to improve
> compatibility with some monitors that didn't seem to set BIT(2).
>
> However, with that change, I've seen occasional issues where the
> detection failed, because BIT(2) was set, but not BIT(0).

I was waiting for a review or testing from a previous lt9611
committer, but seeing as how functionality is being re-introduced in
this patch I think a code review is all that's needed.

>
> Unfortunately, as I understand it, the bits and their function
> was never clearly documented. So lets instead check both
> (BIT(2) | BIT(0)) when checking the register.
>
> Cc: Yongqin Liu <yongqin.liu@...aro.org>
> Cc: Amit Pundir <amit.pundir@...aro.org>
> Cc: Peter Collingbourne <pcc@...gle.com>
> Cc: Vinod Koul <vkoul@...nel.org>
> Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
> Cc: Robert Foss <robert.foss@...aro.org>
> Cc: kernel-team@...roid.com
> Fixes: 19cf41b64e3b ("lontium-lt9611: check a different register bit for HDMI sensing")
> Signed-off-by: John Stultz <jstultz@...gle.com>
> ---
>  drivers/gpu/drm/bridge/lontium-lt9611.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/bridge/lontium-lt9611.c b/drivers/gpu/drm/bridge/lontium-lt9611.c
> index bf66af668f61..a11604a56e08 100644
> --- a/drivers/gpu/drm/bridge/lontium-lt9611.c
> +++ b/drivers/gpu/drm/bridge/lontium-lt9611.c
> @@ -584,7 +584,7 @@ static enum drm_connector_status __lt9611_detect(struct lt9611 *lt9611)
>         int connected = 0;
>
>         regmap_read(lt9611->regmap, 0x825e, &reg_val);
> -       connected  = (reg_val & BIT(0));
> +       connected  = (reg_val & (BIT(2) | BIT(0)));
>
>         lt9611->status = connected ?  connector_status_connected :
>                                 connector_status_disconnected;
> --
> 2.36.0.512.ge40c2bad7a-goog
>

I reviewed this series and it looks good.

Reviewed-by: Robert Foss <robert.foss@...aro.org>

Applied to drm-misc-next.