linux-kernel - Re: [PATCH RFC 0/8] USB Type-C alternate mode selection

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Message-ID: <aTrTvA8Srak1mNGS@kuha>
Date: Thu, 11 Dec 2025 16:22:52 +0200
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>,
	Abel Vesa <abel.vesa@...aro.org>,
	Pooja Katiyar <pooja.katiyar@...el.com>,
	Pavan Holla <pholla@...omium.org>, Madhu M <madhu.m@...el.com>,
	Venkat Jayaraman <venkat.jayaraman@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 0/8] USB Type-C alternate mode selection

Thu, Dec 11, 2025 at 03:40:24PM +0200, Heikki Krogerus kirjoitti:
> Without going into the code review yet, I'm okay with this in general,
> except with the artificial SID for the USB4. I still don't understand
> why do you guys think we should use that instead of an USB4 specific
> device type?
> 
> I think somebody said earlier that the user space can't see the device
> type of the alt modes? If that's really the case, then I think there
> is some bigger issue here. Are you really sure that if you check the
> device type of an alternate mode for example with udevadm, it does not
> say DEVTYPE=typec_alternate_mode ?
> 
>         % udevadm info -q property --property=DEVTYPE /sys/bus/typec/devices/port0-partner.0
>         DEVTYPE=typec_alternate_mode

Or just use grep :)

        % grep DEVTYPE /sys/bus/typec/devices/port0-partner.0/uevent
        DEVTYPE=typec_alternate_mode

So, if that really does not work, then there is a bug somewhere that
we obviously need to fix.

Please note that the port altmodes are now also part of the bus.

Br,

-- 
heikki