linux-kernel - Re: [PATCH v7 1/9] usb: typec: Add notifier functions

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Message-ID: <2025102308-glorified-greedy-e41c@gregkh>
Date: Thu, 23 Oct 2025 13:29:58 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Chaoyi Chen <chaoyi.chen@...k-chips.com>
Cc: Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.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>,
	Andrzej Hajda <andrzej.hajda@...el.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Robert Foss <rfoss@...nel.org>,
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
	Jonas Karlman <jonas@...boo.se>,
	Jernej Skrabec <jernej.skrabec@...il.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>,
	Dragan Simic <dsimic@...jaro.org>, Johan Jonker <jbx6244@...il.com>,
	Diederik de Haas <didi.debian@...ow.org>,
	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 v7 1/9] usb: typec: Add notifier functions

On Thu, Oct 23, 2025 at 07:21:31PM +0800, Chaoyi Chen wrote:
> Hi Heikki,
> 
> On 10/23/2025 5:44 PM, Heikki Krogerus wrote:
> > On Thu, Oct 23, 2025 at 12:04:44PM +0300, Heikki Krogerus wrote:
> > > On Thu, Oct 23, 2025 at 11:10:20AM +0300, Heikki Krogerus wrote:
> > > > Hi,
> > > > 
> > > > > diff --git a/include/linux/usb/typec_notify.h b/include/linux/usb/typec_notify.h
> > > > > new file mode 100644
> > > > > index 000000000000..a3f1f3b3ae47
> > > > > --- /dev/null
> > > > > +++ b/include/linux/usb/typec_notify.h
> > > > > @@ -0,0 +1,17 @@
> > > > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > > > +
> > > > > +#ifndef __USB_TYPEC_NOTIFY
> > > > > +#define __USB_TYPEC_NOTIFY
> > > > > +
> > > > > +#include <linux/notifier.h>
> > > > > +
> > > > > +enum usb_typec_event {
> > > > > +	TYPEC_ALTMODE_REGISTERED
> > > > > +};
> > > > Don't you need to know when the altmode is removed?
> > > I noticed that you don't because drm_dp_hpd_bridge_register() is
> > > always resource managed. But I think you could still send an event
> > > also when the altmode is removed already now. That way it does not
> > > need to be separately added if and when it is needed.
> > Hold on! Every bus has already a notifier chain. That's the one that
> > we should also use. Sorry for not noticing that earlier.
> > 
> > So let's just export the bus type in this patch - you can then use
> > bus_register_notifier() in your driver:
> > 
> > diff --git a/drivers/usb/typec/bus.c b/drivers/usb/typec/bus.c
> > index a884cec9ab7e..65ded9e3cdaa 100644
> > --- a/drivers/usb/typec/bus.c
> > +++ b/drivers/usb/typec/bus.c
> > @@ -547,3 +547,4 @@ const struct bus_type typec_bus = {
> >          .probe = typec_probe,
> >          .remove = typec_remove,
> >   };
> > +EXPORT_SYMBOL_GPL(typec_bus);
> > diff --git a/drivers/usb/typec/bus.h b/drivers/usb/typec/bus.h
> > index 643b8c81786d..af9edb3db9d0 100644
> > --- a/drivers/usb/typec/bus.h
> > +++ b/drivers/usb/typec/bus.h
> > @@ -5,7 +5,6 @@
> >   #include <linux/usb/typec_altmode.h>
> > -struct bus_type;
> >   struct typec_mux;
> >   struct typec_retimer;
> > @@ -28,7 +27,6 @@ struct altmode {
> >   #define to_altmode(d) container_of(d, struct altmode, adev)
> > -extern const struct bus_type typec_bus;
> >   extern const struct device_type typec_altmode_dev_type;
> >   #define is_typec_altmode(_dev_) (_dev_->type == &typec_altmode_dev_type)
> > diff --git a/include/linux/usb/typec.h b/include/linux/usb/typec.h
> > index 309251572e2e..c6fd46902fce 100644
> > --- a/include/linux/usb/typec.h
> > +++ b/include/linux/usb/typec.h
> > @@ -20,12 +20,15 @@ struct typec_port;
> >   struct typec_altmode_ops;
> >   struct typec_cable_ops;
> > +struct bus_type;
> >   struct fwnode_handle;
> >   struct device;
> >   struct usb_power_delivery;
> >   struct usb_power_delivery_desc;
> > +extern const struct bus_type typec_bus;
> > +
> >   enum typec_port_type {
> >          TYPEC_PORT_SRC,
> >          TYPEC_PORT_SNK,
> 
> Thank you for your detailed explanation. I noticed that there is a device_register() action in typec_register_altmode(), so we can just take advantage of this.
> 
> 
> Another thing is that we need to distinguish between different devices in the notifier callback, as typec_register_altmode()/typec_register_partner()/typec_register_plug()/typec_register_cable() may all register devices. Since the data passed in bus_notify() is struct device *dev, I think we can distinguish them through `dev->type.name`? We may already have such names, "typec_alternate_mode", "typec_partner", "typec_plug" in class.c . And then extract these names as macros and put them in the typec header file.
> 
> 
> Or do you have any better ideas? Thank you.

Check based on the type itself, NOT on the type name, as all device
types on a bus should be unique.  If the structure for that is not
properly exported for you to use, just export it.

thanks,

greg k-h