linux-kernel - Re: [PATCH 6.1,6.2,6.3 v3 1/6] counter: 104-quad-8: Fix race condition between FLAG and CNTR reads

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Message-ID: <ZBW8XN71fYwJe6rW@ishi>
Date:   Sat, 18 Mar 2023 09:27:56 -0400
From:   William Breathitt Gray <wbg@...nel.org>
To:     William Breathitt Gray <william.gray@...aro.org>
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        jic23@...nel.org, lars@...afoo.de, stable@...r.kernel.org
Subject: Re: [PATCH 6.1,6.2,6.3 v3 1/6] counter: 104-quad-8: Fix race
 condition between FLAG and CNTR reads

On Sun, Mar 12, 2023 at 07:15:49PM -0400, William Breathitt Gray wrote:
> The Counter (CNTR) register is 24 bits wide, but we can have an
> effective 25-bit count value by setting bit 24 to the XOR of the Borrow
> flag and Carry flag. The flags can be read from the FLAG register, but a
> race condition exists: the Borrow flag and Carry flag are instantaneous
> and could change by the time the count value is read from the CNTR
> register.
> 
> Since the race condition could result in an incorrect 25-bit count
> value, remove support for 25-bit count values from this driver;
> hard-coded maximum count values are replaced by a LS7267_CNTR_MAX define
> for consistency and clarity.
> 
> Fixes: 28e5d3bb0325 ("iio: 104-quad-8: Add IIO support for the ACCES 104-QUAD-8")
> Cc: <stable@...r.kernel.org> # 6.1.x
> Cc: <stable@...r.kernel.org> # 6.2.x
> Signed-off-by: William Breathitt Gray <william.gray@...aro.org>

Applied to counter-fixes.

William Breathitt Gray

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