Re:[PATCH v11 04/21] drm/bridge: synopsys: dw-dp: Document missing reset line deassert

From: "Andy Yan" <andyshrk@163.com>
To: "Sebastian Reichel" <sebastian.reichel@collabora.com>
Cc: "Heiko Stübner" <heiko@sntech.de>,
	Sashiko <sashiko-bot@kernel.org>,
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
	"Laurent Pinchart" <Laurent.pinchart@ideasonboard.com>,
	"Andrzej Hajda" <andrzej.hajda@intel.com>,
	kernel@collabora.com, "David Airlie" <airlied@gmail.com>,
	"Simona Vetter" <simona@ffwll.ch>,
	"Rob Herring" <robh@kernel.org>, "Robert Foss" <rfoss@kernel.org>,
	"Jernej Skrabec" <jernej.skrabec@gmail.com>,
	linux-rockchip@lists.infradead.org,
	"Luca Ceresoli" <luca.ceresoli@bootlin.com>,
	devicetree@vger.kernel.org, "Conor Dooley" <conor+dt@kernel.org>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"Jonas Karlman" <jonas@kwiboo.se>,
	"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	"Maxime Ripard" <mripard@kernel.org>,
	"Alexey Charkov" <alchark@flipper.net>,
	"Damon Ding" <damon.ding@rock-chips.com>,
	linux-arm-kernel@lists.infradead.org,
	"Dmitry Baryshkov" <dmitry.baryshkov@oss.qualcomm.com>,
	"Neil Armstrong" <neil.armstrong@linaro.org>,
	"Dmitry Baryshkov" <lumag@kernel.org>,
	"Sandy Huang" <hjc@rock-chips.com>,
	"Philipp Zabel" <p.zabel@pengutronix.de>,
	"Andy Yan" <andy.yan@rock-chips.com>,
	"Krzysztof Kozlowski" <krzk+dt@kernel.org>
Subject: Re:[PATCH v11 04/21] drm/bridge: synopsys: dw-dp: Document missing reset line deassert
Date: Sun, 16 Aug 2026 20:47:08 +0800 (CST)	[thread overview]
Message-ID: <2b761354.18f3.1a00a9c9379.Coremail.andyshrk@163.com> (raw)
In-Reply-To: <20260806-synopsys-dw-dp-improvements-v11-4-0d508505f383@collabora.com>

Hello Sebastian,

At 2026-08-07 01:02:10, "Sebastian Reichel" <sebastian.reichel@collabora.com> wrote:
>If the driver uses devm_reset_control_get_exclusive_deasserted() instead
>of devm_reset_control_get() and thus automatically deasserts during
>probe, the SoC will hang when the device is unbound.
>
>This does not happen, when runtime PM is being used (not yet supported
>in mainline), which suggests the power-domain involved requires this reset
>line to be deasserted.
>
>Even with runtime PM there is no gurantee that the power-domain is
>disabled as it is shared. Considering the power-domain does not have
>the reset dependency described in DT, document the problem but leave
>things in the current state until a better solution is found as the
>reset line is deasserted by default on all supported platforms.
>
>Reported-by: Sashiko <sashiko-bot@kernel.org>
>Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

   Reviewed-by: Andy Yan <andy.yan@rock-chips.com>
>---
> drivers/gpu/drm/bridge/synopsys/dw-dp.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
>diff --git a/drivers/gpu/drm/bridge/synopsys/dw-dp.c b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
>index 21d60e89126f..52e3b37259a6 100644
>--- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
>+++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
>@@ -2090,6 +2090,10 @@ struct dw_dp *dw_dp_probe(struct platform_device *pdev, const struct dw_dp_plat_
> 		return ERR_CAST(dp->hdcp_clk);
> 	}
> 
>+	/*
>+	 * This reset line is deasserted by default; asserting it hangs the SoC if the
>+	 * related power-domain is still active.
>+	 */
> 	dp->rstc = devm_reset_control_get(dev, NULL);
> 	if (IS_ERR(dp->rstc)) {
> 		dev_err_probe(dev, PTR_ERR(dp->rstc), "failed to get reset control\n");
>
>-- 
>2.53.0
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