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

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Message-ID: <aPn4-S7upPOOtenr@kuha.fi.intel.com>
Date: Thu, 23 Oct 2025 12:44:25 +0300
From: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To: Chaoyi Chen <kernel@...kyi.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	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>,
	Chaoyi Chen <chaoyi.chen@...k-chips.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 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,

thanks,

-- 
heikki