linux-kernel - Re: [RFC PATCH 2/3] usb: typec: Add product_type sysfs attribute file for partners and cables

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Date:   Wed, 18 Nov 2020 10:53:50 -0800
From:   Prashant Malani <pmalani@...omium.org>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Benson Leung <bleung@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [RFC PATCH 2/3] usb: typec: Add product_type sysfs attribute
 file for partners and cables

Hi Heikki,

On Wed, Nov 18, 2020 at 06:00:58PM +0300, Heikki Krogerus wrote:
> USB Power Delivery Specification defines a set of product
> types for partners and cables. The product type is defined
> in the ID Header VDO, which is the first object in the
> response to the Discover Identity command.
> 
> This sysfs attribute file is only created for the partners
> and cables if the product type is really known in the
> driver. Some interfaces do not give access to the Discover
> Identity response from the partner or cable, but they may
> still supply the product type separately in some cases.
> 
> When the product type of the partner or cable is detected,
> uevent is also raised with PRODUCT_TYPE set to show the
> actual product type (for example PRODUCT_TYPE=host).
> 
> Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>

I tried this out with the following peripherals:
- Thunderbolt 3 active cable.
- Thunderbolt 3 passive cable.
- Dell WD19TB dock.
- Type C DisplayPort enabled monitor (which advertises as AMA).

For the above, the product_type seems to be getting parsed and displayed
correctly, so FWIW:

Tested-by: Prashant Malani <pmalani@...omium.org>

> ---
>  Documentation/ABI/testing/sysfs-class-typec |  55 ++++++++
>  drivers/usb/typec/class.c                   | 132 ++++++++++++++++++--
>  2 files changed, 180 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-typec b/Documentation/ABI/testing/sysfs-class-typec
> index b7794e02ad205..4c09e327c62be 100644
> --- a/Documentation/ABI/testing/sysfs-class-typec
> +++ b/Documentation/ABI/testing/sysfs-class-typec
> @@ -139,6 +139,42 @@ Description:
>  		Shows if the partner supports USB Power Delivery communication:
>  		Valid values: yes, no
>  
> +What:		/sys/class/typec/<port>-partner/product_type
> +Date:		December 2020
> +Contact:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> +Description:	USB Power Delivery Specification defines a set of product types
> +		for the partner devices. This file will show the product type of
> +		the partner if it is known. Dual-role capable partners will have
> +		both UFP and DFP product types defined, but only one that
> +		matches the current role will be active at the time. If the
> +		product type of the partner is not visible to the device driver,
> +		this file will not exist.
> +
> +		When the partner product type is detected, or changed with role
> +		swap, uvevent is also raised that contains PRODUCT_TYPE=<product
> +		type> (for example PRODUCT_TYPE=hub).
> +
> +		Valid values:
> +
> +		UFP / device role
> +		========================  ==========================
> +		undefined		  -
> +		hub			  PDUSB Hub
> +		peripheral		  PDUSB Peripheral
> +		psd			  Power Bank
> +		ama			  Alternate Mode Adapter
> +		vpd			  VCONN Powered USB Device
> +		========================  ==========================
> +
> +		DFP / host role
> +		========================  ==========================
> +		undefined		  -
> +		hub			  PDUSB Hub
> +		host			  PDUSB Host
> +		power_brick		  Power Brick
> +		amc			  Alternate Mode Controller
> +		========================  ==========================
> +
>  What:		/sys/class/typec/<port>-partner>/identity/
>  Date:		April 2017
>  Contact:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> @@ -202,6 +238,25 @@ Description:
>  		- type-c
>  		- captive
>  
> +What:		/sys/class/typec/<port>-cable/product_type
> +Date:		December 2020
> +Contact:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> +Description:	USB Power Delivery Specification defines a set of product types
> +		for the cables. This file will show the product type of the
> +		cable if it is known. If the product type of the cable is not
> +		visible to the device driver, this file will not exist.
> +
> +		When the cable product type is detected, uvevent is also raised
> +		with PRODUCT_TYPE showing the product type of the cable.
> +
> +		Valid values:
> +
> +		========================  ==========================
> +		undefined		  -
> +		active			  Active Cable
> +		passive			  Passive Cable
> +		========================  ==========================

There exists a /sys/class/typec/<port>-cable/type attribute (connected
to the "active" field in struct typec_cable [1]), which is supposed
to be populated by the Type C port driver. Won't the newly introduced
attribute duplicate the same information as "type"?

[1]
https://elixir.bootlin.com/linux/v5.10-rc4/source/include/linux/usb/typec.h#L170

Thanks,

-Prashant