linux-kernel - Re: [PATCH] drm/bridge: analogix_dp: Fix connector status detection for bridges

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Message-ID: <v6aqic6kffc3x42dkb4bika5tvoqdpmmloroqio2656g74pkws@7fe3bsfzbasn>
Date: Fri, 10 Oct 2025 01:30:11 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Heiko Stuebner <heiko@...ech.de>
Cc: damon.ding@...k-chips.com, m.szyprowski@...sung.com,
        andrzej.hajda@...el.com, neil.armstrong@...aro.org, rfoss@...nel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH] drm/bridge: analogix_dp: Fix connector status detection
 for bridges

On Thu, Oct 09, 2025 at 09:30:28PM +0200, Heiko Stuebner wrote:
> Right now if there is a next bridge attached to the analogix-dp controller
> the driver always assumes this bridge is connected to something, but this
> is of course not always true, as that bridge could also be a hotpluggable
> dp port for example.
> 
> On the other hand, as stated in commit cb640b2ca546 ("drm/bridge: display-
> connector: don't set OP_DETECT for DisplayPorts"), "Detecting the monitor
> for DisplayPort targets is more complicated than just reading the HPD pin
> level" and we should be "letting the actual DP driver perform detection."
> 
> So use drm_bridge_detect() to detect the next bridge's state but ignore
> that bridge if the analogix-dp is handling the hpd-gpio.
> 
> Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> ---
> As this patch stands, it would go on top of v6 of Damon's bridge-connector
> work, but could very well be also integrated into one of the changes there.
> 
> I don't know yet if my ordering and/or reasoning is the correct one or if
> a better handling could be done, but with that change I do get a nice
> hotplug behaviour on my rk3588-tiger-dp-carrier board, where the
> Analogix-DP ends in a full size DP port.
> 
>  drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> index c04b5829712b..cdc56e83b576 100644
> --- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> +++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> @@ -983,8 +983,12 @@ analogix_dp_bridge_detect(struct drm_bridge *bridge, struct drm_connector *conne
>  	struct analogix_dp_device *dp = to_dp(bridge);
>  	enum drm_connector_status status = connector_status_disconnected;
>  
> -	if (dp->plat_data->next_bridge)
> -		return connector_status_connected;
> +	/*
> +	 * An optional next bridge should be in charge of detection the
> +	 * connection status, except if we manage a actual hpd gpio.
> +	 */
> +	if (dp->plat_data->next_bridge && !dp->hpd_gpiod)
> +		return drm_bridge_detect(dp->plat_data->next_bridge, connector);

And it's also not correct because the next bridge might be a retimer
with the bridge next to it being a one with the actual detection
capabilities. drm_bridge_connector solves that in a much better way. See
the series at [1]

[1] https://lore.kernel.org/dri-devel/41c2a141-a72e-4780-ab32-f22f3a2e0179@samsung.com/

>  
>  	if (!analogix_dp_detect_hpd(dp))
>  		status = connector_status_connected;
> -- 
> 2.47.2
> 

-- 
With best wishes
Dmitry