linux-kernel - Re: [PATCH v1 1/5] usb: typec: Add alt_mode

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Message-ID: <aKWpI0RhPR2mFlql@kuha.fi.intel.com>
Date: Wed, 20 Aug 2025 13:53:23 +0300
From: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To: Andrei Kuchynski <akuchynski@...omium.org>
Cc: Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
	Benson Leung <bleung@...omium.org>,
	Jameson Thies <jthies@...gle.com>,
	Tzung-Bi Shih <tzungbi@...nel.org>, linux-usb@...r.kernel.org,
	chrome-platform@...ts.linux.dev,
	Guenter Roeck <groeck@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
	"Christian A. Ehrhardt" <lk@...e.de>,
	Venkat Jayaraman <venkat.jayaraman@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/5] usb: typec: Add alt_mode_override field to port
 property

On Thu, Aug 14, 2025 at 06:44:51PM +0000, Andrei Kuchynski wrote:
> This new field in the port properties dictates whether the Platform Policy
> Manager (PPM) allows the OS Policy Manager (OPM) to change the currently
> active, negotiated alternate mode.
> 
> Signed-off-by: Andrei Kuchynski <akuchynski@...omium.org>
> ---
>  drivers/usb/typec/class.c | 14 +++++++++++---
>  drivers/usb/typec/class.h |  2 ++
>  include/linux/usb/typec.h |  1 +
>  3 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/typec/class.c b/drivers/usb/typec/class.c
> index 67a533e35150..a72325ff099a 100644
> --- a/drivers/usb/typec/class.c
> +++ b/drivers/usb/typec/class.c
> @@ -459,9 +459,16 @@ static umode_t typec_altmode_attr_is_visible(struct kobject *kobj,
>  	struct typec_altmode *adev = to_typec_altmode(kobj_to_dev(kobj));
>  
>  	if (attr == &dev_attr_active.attr)
> -		if (!is_typec_port(adev->dev.parent) &&
> -		    (!adev->ops || !adev->ops->activate))
> -			return 0444;
> +		if (!is_typec_port(adev->dev.parent)) {
> +			struct typec_partner *partner =
> +				to_typec_partner(adev->dev.parent);

That looks a bit unnecessary. Also, can't the altmode be a plug alt mode?

> +			struct typec_port *port =
> +				to_typec_port(partner->dev.parent);
> +
> +			if (!port->alt_mode_override || !adev->ops ||
> +				!adev->ops->activate)
> +				return 0444;
> +		}

How about:

	struct typec_altmode *adev = to_typec_altmode(kobj_to_dev(kobj));
        struct typec_port *port = typec_altmode2port(adev);

        if (attr == &dev_attr_active.attr) {
               if (!is_typec_port(adev->dev.parent)) {
                        if (!port->alt_mode_override || !adev->ops || !adev->ops->activate)
                                return 0444;
                }
        }

>  	return attr->mode;
>  }
> @@ -2681,6 +2688,7 @@ struct typec_port *typec_register_port(struct device *parent,
>  	}
>  
>  	port->pd = cap->pd;
> +	port->alt_mode_override = cap->alt_mode_override;

This needs to be enabled by default:

	port->alt_mode_override = !cap->no_mode_control;

>  	ret = device_add(&port->dev);
>  	if (ret) {
> diff --git a/drivers/usb/typec/class.h b/drivers/usb/typec/class.h
> index db2fe96c48ff..f05d9201c233 100644
> --- a/drivers/usb/typec/class.h
> +++ b/drivers/usb/typec/class.h
> @@ -80,6 +80,8 @@ struct typec_port {
>  	 */
>  	struct device			*usb2_dev;
>  	struct device			*usb3_dev;
> +
> +	bool				alt_mode_override;

s/alt_mode_override/mode_control/ ?

>  };
>  
>  #define to_typec_port(_dev_) container_of(_dev_, struct typec_port, dev)
> diff --git a/include/linux/usb/typec.h b/include/linux/usb/typec.h
> index 252af3f77039..6e09e68788dd 100644
> --- a/include/linux/usb/typec.h
> +++ b/include/linux/usb/typec.h
> @@ -304,6 +304,7 @@ struct typec_capability {
>  	enum typec_accessory	accessory[TYPEC_MAX_ACCESSORY];
>  	unsigned int		orientation_aware:1;
>  	u8			usb_capability;
> +	bool			alt_mode_override;
>  
>  	struct fwnode_handle	*fwnode;
>  	void			*driver_data;
> -- 
> 2.51.0.rc0.215.g125493bb4a-goog

-- 
heikki