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

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Message-ID: <9c52db41-14f3-41a8-9423-3efe604361aa@rock-chips.com>
Date: Thu, 23 Oct 2025 19:21:31 +0800
From: Chaoyi Chen <chaoyi.chen@...k-chips.com>
To: Heikki Krogerus <heikki.krogerus@...ux.intel.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

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.


> thanks,
>
-- 
Best,
Chaoyi