linux-kernel - Re: [PATCH 0/5] Fix various races in UCSI

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Date: Fri, 22 Mar 2024 12:02:58 +0200
From: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To: "Christian A. Ehrhardt" <lk@...e.de>
Cc: linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Prashant Malani <pmalani@...omium.org>,
	Jameson Thies <jthies@...gle.com>,
	Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
	Samuel Čavoj <samuel@...oj.net>,
	linux-usb@...r.kernel.org, Kenneth Crudup <kenny@...ix.com>
Subject: Re: [PATCH 0/5] Fix various races in UCSI

On Wed, Mar 20, 2024 at 08:39:21AM +0100, Christian A. Ehrhardt wrote:
> Fix various races in UCSI code:
> - The EVENT_PENDING bit should be cleared under the PPM lock to
>   avoid spurious re-checking of the connector status.
> - The initial connector change notification during init may be
>   lost which can cause a stuck UCSI controller. Observed by me
>   and others during resume or after module reload.
> - Unsupported commands must be ACKed. This was uncovered by the
>   recent change from Jameson Thies that did sent unsupported commands.
> - The DELL quirk still isn't quite complete and I've found a more
>   elegant way to handle this. A connector change ack _is_ accepted
>   on affected systems if it is bundled with a command ack.
> - If we do two consecutive resets or the controller is already
>   reset at boog the second reset might complete early because the
>   reset complete bit is already set. ucsi_ccg.c has a work around
>   for this but it looks like an more general issue to me.
> 
> NOTE:
> As a result of these individual fixes we could think about the
> question if there are additional cases where we send some type
> of command to the PPM while the bit that indicates its completion
> is already set in CCI. And in fact there is one more case where
> this can happen: The ack command that clears the connector change
> is sent directly after the ack command for the previous command.
> It might be possible to simply ack the connector change along with
> the first command ucsi_handle_connector_change() and not at the
> end. AFAICS the connector lock should protect us from races that
> might arise out of this.

That sounds good to me.

thanks,

-- 
heikki