linux-kernel - Re: [PATCH v3 4/5] usb: typec: Implement alternate mode priority handling

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Message-ID: <2025091029-snarl-decimal-aea2@gregkh>
Date: Wed, 10 Sep 2025 15:31:37 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Andrei Kuchynski <akuchynski@...omium.org>
Cc: Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	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>,
	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 v3 4/5] usb: typec: Implement alternate mode priority
 handling

On Fri, Sep 05, 2025 at 02:22:05PM +0000, Andrei Kuchynski wrote:
> This patch introduces APIs to manage the priority of USB Type-C alternate
> modes. These APIs allow for setting and retrieving a priority number for
> each mode. If a new priority value conflicts with an existing mode's
> priority, the priorities of the conflicting mode and all subsequent modes
> are automatically incremented to ensure uniqueness.
> 
> Signed-off-by: Andrei Kuchynski <akuchynski@...omium.org>
> ---
>  drivers/usb/typec/Makefile         |  2 +-
>  drivers/usb/typec/mode_selection.c | 38 ++++++++++++++++++++++++++++++
>  drivers/usb/typec/mode_selection.h |  6 +++++
>  include/linux/usb/typec_altmode.h  |  1 +
>  4 files changed, 46 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/usb/typec/mode_selection.c
>  create mode 100644 drivers/usb/typec/mode_selection.h
> 
> diff --git a/drivers/usb/typec/Makefile b/drivers/usb/typec/Makefile
> index 7a368fea61bc..8a6a1c663eb6 100644
> --- a/drivers/usb/typec/Makefile
> +++ b/drivers/usb/typec/Makefile
> @@ -1,6 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0
>  obj-$(CONFIG_TYPEC)		+= typec.o
> -typec-y				:= class.o mux.o bus.o pd.o retimer.o
> +typec-y				:= class.o mux.o bus.o pd.o retimer.o mode_selection.o
>  typec-$(CONFIG_ACPI)		+= port-mapper.o
>  obj-$(CONFIG_TYPEC)		+= altmodes/
>  obj-$(CONFIG_TYPEC_TCPM)	+= tcpm/
> diff --git a/drivers/usb/typec/mode_selection.c b/drivers/usb/typec/mode_selection.c
> new file mode 100644
> index 000000000000..2179bf25f5d4
> --- /dev/null
> +++ b/drivers/usb/typec/mode_selection.c
> @@ -0,0 +1,38 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright 2025 Google LLC.
> + */
> +
> +#include "mode_selection.h"
> +#include "class.h"
> +#include "bus.h"
> +
> +static int increment_duplicated_priority(struct device *dev, void *data)
> +{
> +	struct typec_altmode **alt_target = (struct typec_altmode **)data;
> +
> +	if (is_typec_altmode(dev)) {
> +		struct typec_altmode *alt = to_typec_altmode(dev);
> +
> +		if (alt != *alt_target && alt->priority == (*alt_target)->priority) {
> +			alt->priority++;
> +			*alt_target = alt;
> +			return 1;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +void typec_mode_set_priority(struct typec_altmode *alt,
> +		const unsigned int priority)
> +{
> +	struct typec_port *port = to_typec_port(alt->dev.parent);
> +	int res = 1;
> +
> +	alt->priority = priority;
> +
> +	while (res)
> +		res = device_for_each_child(&port->dev, &alt,
> +				increment_duplicated_priority);
> +}
> diff --git a/drivers/usb/typec/mode_selection.h b/drivers/usb/typec/mode_selection.h
> new file mode 100644
> index 000000000000..cbf5a37e6404
> --- /dev/null
> +++ b/drivers/usb/typec/mode_selection.h
> @@ -0,0 +1,6 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#include <linux/usb/typec_altmode.h>
> +
> +void typec_mode_set_priority(struct typec_altmode *alt,
> +		const unsigned int priority);
> diff --git a/include/linux/usb/typec_altmode.h b/include/linux/usb/typec_altmode.h
> index b3c0866ea70f..571c6e00b54f 100644
> --- a/include/linux/usb/typec_altmode.h
> +++ b/include/linux/usb/typec_altmode.h
> @@ -28,6 +28,7 @@ struct typec_altmode {
>  	int				mode;
>  	u32				vdo;
>  	unsigned int			active:1;
> +	unsigned int			priority;

What is the range of this?  And this value is only incremented, never
decremented?

thanks,

greg k-h