Re: [PATCH v3 08/10] drm/rockchip: dw_dp: Add runtime PM support

From: Sebastian Reichel <sebastian.reichel@collabora.com>
To: Andy Yan <andyshrk@gmail.com>
Cc: "Heiko Stübner" <heiko@sntech.de>,
	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>,
	"Jonas Karlman" <jonas@kwiboo.se>,
	"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	"Maxime Ripard" <mripard@kernel.org>,
	"Damon Ding" <damon.ding@rock-chips.com>,
	yubing.zhang@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>,
	"Alexey Charkov" <alchark@gmail.com>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"Andy Yan" <andy.yan@rock-chips.com>,
	"Krzysztof Kozlowski" <krzk+dt@kernel.org>
Subject: Re: [PATCH v3 08/10] drm/rockchip: dw_dp: Add runtime PM support
Date: Wed, 15 Jul 2026 21:00:12 +0200	[thread overview]
Message-ID: <alfV1691ZgZ6KylX@venus> (raw)
In-Reply-To: <CANbgqATR-V0rRGfzj0hdJ2hsJex-iWzHMwD1L4vavTi2Jd79Kw@mail.gmail.com>

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Hello Andy,

On Tue, Jul 14, 2026 at 06:08:06PM +0800, Andy Yan wrote:
> > @@ -58,6 +59,8 @@ static void dw_dp_rockchip_hpd_sw_sel(void *data, bool
> > force_hpd_from_sw)
> >
> >         dp->hpd_sel = force_hpd_from_sw;
> >
> > +       ACQUIRE(pm_runtime_active_auto, pm)(dp->dev);
> 
> This can triger  HPD irq for USB-C DP AltMode, but for a standard
> DP port, this is no way to acquire runtime, so there will no irq
> when plug in.

Right. I don't have any RK3588 or RK3576 system exposing a DP
connector directly. This this is non-trivial to test for me :/

I see the following options:

1. Only enable runtime PM when running in USB-C mode
2. Mux the HPD pin as GPIO to support waking up with the controller
   being suspended; either remux when the controller is awake or use
   the same mechanism as USB-C to do software based HPD on top of the
   GPIO (which would allow using any GPIO as HPD).
3. Have a poll function, which wakes up the controller regularly to
   check the status

I consider going for option 1 for now, which allows option 2 to be
implemented as a follow up. Mostly to avoid that the series becomes
as big and messy as the USBDP PHY series became.

Greetings,

-- Sebastian

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