Re: [PATCH v10 43/69] drm/vc4: hdmi: Propagate -EDEADLK to the top level

From: Maxime Ripard <mripard@kernel.org>
To: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Cc: "Andrzej Hajda" <andrzej.hajda@intel.com>,
	"Neil Armstrong" <neil.armstrong@linaro.org>,
	"Robert Foss" <rfoss@kernel.org>,
	"Laurent Pinchart" <Laurent.pinchart@ideasonboard.com>,
	"Jonas Karlman" <jonas@kwiboo.se>,
	"Jernej Skrabec" <jernej.skrabec@gmail.com>,
	"Luca Ceresoli" <luca.ceresoli@bootlin.com>,
	"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"David Airlie" <airlied@gmail.com>,
	"Simona Vetter" <simona@ffwll.ch>,
	"Chen-Yu Tsai" <wens@kernel.org>,
	"Samuel Holland" <samuel@sholland.org>,
	"Dave Stevenson" <dave.stevenson@raspberrypi.com>,
	"Maíra Canal" <mcanal@igalia.com>,
	"Raspberry Pi Kernel Maintenance" <kernel-list@raspberrypi.com>,
	"Sandy Huang" <hjc@rock-chips.com>,
	"Heiko Stübner" <heiko@sntech.de>,
	"Andy Yan" <andy.yan@rock-chips.com>,
	"Algea Cao" <algea.cao@rock-chips.com>,
	"Daniel Stone" <daniels@collabora.com>,
	"Liu Ying" <victor.liu@nxp.com>, "Phong LE" <ple@baylibre.com>,
	kernel@collabora.com, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org,
	linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev, linux-rockchip@lists.infradead.org
Subject: Re: [PATCH v10 43/69] drm/vc4: hdmi: Propagate -EDEADLK to the top level
Date: Thu, 20 Aug 2026 10:55:09 +0200	[thread overview]
Message-ID: <20260820-sceptical-friendly-panther-6cdfd4@houat> (raw)
In-Reply-To: <20260731-dw-hdmi-qp-scramb-v10-43-294364b2cf15@collabora.com>

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On Fri, Jul 31, 2026 at 07:19:50PM +0300, Cristian Ciocaltea wrote:
> drm_connector_helper_funcs.detect_ctx() is expected to propagate
> -EDEADLK so that context owners, e.g. drm_helper_probe_detect_ctx(), can
> perform the required backoff and retry.
> 
> vc4_hdmi_handle_hotplug() instead runs its own retry loop and calls
> drm_modeset_backoff() on an acquire context it does not own.  This drops
> all locks in the context, including connection_mutex held by the core.
> 
> Drop the local retry logic and propagate -EDEADLK to the caller instead.
> This aligns VC4 with the expected detect_ctx() semantics.
> 
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
> ---
>  drivers/gpu/drm/vc4/vc4_hdmi.c | 23 +++++++----------------
>  1 file changed, 7 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index ba16e7944cf3..72042fad04c5 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -344,12 +344,11 @@ static int vc4_hdmi_reset_link(struct drm_connector *connector,
>  	return drm_atomic_helper_reset_crtc(crtc, ctx);
>  }
>  
> -static void vc4_hdmi_handle_hotplug(struct vc4_hdmi *vc4_hdmi,
> -				    struct drm_modeset_acquire_ctx *ctx,
> -				    enum drm_connector_status status)
> +static int vc4_hdmi_handle_hotplug(struct vc4_hdmi *vc4_hdmi,
> +				   struct drm_modeset_acquire_ctx *ctx,
> +				   enum drm_connector_status status)
>  {
>  	struct drm_connector *connector = &vc4_hdmi->connector;
> -	int ret;
>  
>  	/*
>  	 * NOTE: This function should really be called with vc4_hdmi->mutex
> @@ -368,17 +367,9 @@ static void vc4_hdmi_handle_hotplug(struct vc4_hdmi *vc4_hdmi,
>  	drm_atomic_helper_connector_hdmi_hotplug(connector, ctx, status);
>  
>  	if (status != connector_status_connected)
> -		return;
> +		return 0;
>  
> -	for (;;) {
> -		ret = vc4_hdmi_reset_link(connector, ctx);
> -		if (ret == -EDEADLK) {
> -			drm_modeset_backoff(ctx);
> -			continue;
> -		}
> -
> -		break;
> -	}
> +	return vc4_hdmi_reset_link(connector, ctx);
>  }
>  
>  static int vc4_hdmi_connector_detect_ctx(struct drm_connector *connector,
> @@ -416,10 +407,10 @@ static int vc4_hdmi_connector_detect_ctx(struct drm_connector *connector,
>  			status = connector_status_connected;
>  	}
>  
> -	vc4_hdmi_handle_hotplug(vc4_hdmi, ctx, status);
> +	ret = vc4_hdmi_handle_hotplug(vc4_hdmi, ctx, status);
>  	pm_runtime_put(&vc4_hdmi->pdev->dev);
>  
> -	return status;
> +	return ret == -EDEADLK ? ret : status;

Don't we mask any error that isn't EDEADLK here?

Maxime

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