linux-kernel - Re: [PATCH v6 1/8] usb: typec: Add default HPD device when register DisplayPort altmode

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Message-ID: <aPdI7Vb_djrfCfbT@kuha.fi.intel.com>
Date: Tue, 21 Oct 2025 11:48:45 +0300
From: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To: Chaoyi Chen <chaoyi.chen@...k-chips.com>
Cc: Chaoyi Chen <kernel@...kyi.com>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Vinod Koul <vkoul@...nel.org>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Heiko Stuebner <heiko@...ech.de>, Sandy Huang <hjc@...k-chips.com>,
	Andy Yan <andy.yan@...k-chips.com>,
	Yubing Zhang <yubing.zhang@...k-chips.com>,
	Frank Wang <frank.wang@...k-chips.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Amit Sunil Dhamne <amitsd@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dragan Simic <dsimic@...jaro.org>, Johan Jonker <jbx6244@...il.com>,
	Diederik de Haas <didi.debian@...ow.org>,
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
	Peter Robinson <pbrobinson@...il.com>, linux-usb@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-phy@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v6 1/8] usb: typec: Add default HPD device when register
 DisplayPort altmode

Hi,

On Mon, Oct 20, 2025 at 07:07:46PM +0800, Chaoyi Chen wrote:
> Hi Heikki,
> 
> On 10/20/2025 6:02 PM, Heikki Krogerus wrote:
> > On Thu, Oct 16, 2025 at 10:27:34AM +0800, Chaoyi Chen wrote:
> > > From: Chaoyi Chen <chaoyi.chen@...k-chips.com>
> > > 
> > > Add default DRM AUX HPD bridge device when register DisplayPort
> > > altmode. That makes it redundant for each Type-C driver to implement
> > > a similar registration process in embedded scenarios.
> > > 
> > > Signed-off-by: Chaoyi Chen <chaoyi.chen@...k-chips.com>
> > > ---
> > > 
> > > Changes in v6:
> > > - Fix depend in Kconfig.
> > > 
> > > Changes in v5:
> > > - Remove the calls related to `drm_aux_hpd_bridge_notify()`.
> > > - Place the helper functions in the same compilation unit.
> > > - Add more comments about parent device.
> > > 
> > >   drivers/usb/typec/Kconfig         |  2 ++
> > >   drivers/usb/typec/class.c         | 26 ++++++++++++++++++++++++++
> > >   include/linux/usb/typec_altmode.h |  2 ++
> > >   3 files changed, 30 insertions(+)
> > > 
> > > diff --git a/drivers/usb/typec/Kconfig b/drivers/usb/typec/Kconfig
> > > index 2f80c2792dbd..a6730fbb576b 100644
> > > --- a/drivers/usb/typec/Kconfig
> > > +++ b/drivers/usb/typec/Kconfig
> > > @@ -2,6 +2,8 @@
> > >   menuconfig TYPEC
> > >   	tristate "USB Type-C Support"
> > > +	depends on DRM || DRM=n
> > > +	select DRM_AUX_HPD_BRIDGE if DRM_BRIDGE && OF
> > This is wrong. DRM should not dictate how this entire subsystem core
> > is configured. The dependency needs to be on the DRM bridge side.
> > 
> > You can for example use the bus notification there to see when a new
> > alternate mode is being registered, or use some other notification
> > mechanism.
> 
> Is it a good idea to implement notification functions like
> drivers/usb/core/notify.c in TCPM, and then let other subsystems (such as DRM)
> listen to these notifications?

Don't limit this to tcpm only. I would suggest something similar what
we have for usb bus: drivers/usb/core/notify.c

So that, but for the typec bus. Then in DRM bridge code you just use
typec_register/unregister_notify().

thanks,

-- 
heikki