linux-kernel - Re: [PATCH v2 2/2] platform/chrome: cros_ec

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Message-ID: <CACKy9TJHtA5K2YqdNdnMuTvOsz4OCkRds4Hbj8aZdK5VXpMgWw@mail.gmail.com>
Date: Mon, 14 Jul 2025 10:32:03 +0200
From: Radu Vele <raduvele@...gle.com>
To: Tzung-Bi Shih <tzungbi@...nel.org>
Cc: Benson Leung <bleung@...omium.org>, 
	Abhishek Pandit-Subedi <abhishekpandit@...omium.org>, Jameson Thies <jthies@...gle.com>, 
	Andrei Kuchynski <akuchynski@...omium.org>, chrome-platform@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] platform/chrome: cros_ec_typec: Add lock per-port

On Fri, Jul 11, 2025 at 6:12 AM Tzung-Bi Shih <tzungbi@...nel.org> wrote:
>
> On Fri, Jul 11, 2025 at 12:35:02AM +0000, Radu Vele wrote:
> > Add a lock associated to each port to protect port data against
> > concurrent access. Concurrency may result from sysfs commands
> > and ec events.
>
> I realized the critical sections are way too large.  What exactly data the
> lock tries to protect?  Is the race possibility introduced by any previous
> commits?  Please provide more context.

With the implementation of the role swap operations from the previous
commit (and also enter usb mode from another recent commit) we
introduce the possibility of concurrent access to the cros_ec_typec port
data from the userspace (e.g. trigger a power role swap from sysfs) vs
from EC events (e.g. partner triggered a role swap that we accept).
This is the main reason to propose a per-port lock. This way we ensure
we protect the state of each port in the cros_ec_typec driver.