linux-kernel - Re: [PATCH] i2c: pasemi: Wait for write xfers to finish

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Date:   Fri, 15 Apr 2022 23:12:28 +0200
From:   Wolfram Sang <wsa@...nel.org>
To:     Martin Povišer <povik+lin@...ebit.org>
Cc:     Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>,
        Michael Ellerman <mpe@...erman.id.au>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Jean Delvare <khali@...ux-fr.org>,
        Olof Johansson <olof@...om.net>,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, Janne Grunau <j@...nau.net>
Subject: Re: [PATCH] i2c: pasemi: Wait for write xfers to finish

On Tue, Mar 29, 2022 at 08:38:17PM +0200, Martin Povišer wrote:
> Wait for completion of write transfers before returning from the driver.
> At first sight it may seem advantageous to leave write transfers queued
> for the controller to carry out on its own time, but there's a couple of
> issues with it:
> 
>  * Driver doesn't check for FIFO space.
> 
>  * The queued writes can complete while the driver is in its I2C read
>    transfer path which means it will get confused by the raising of
>    XEN (the 'transaction ended' signal). This can cause a spurious
>    ENODATA error due to premature reading of the MRXFIFO register.
> 
> Adding the wait fixes some unreliability issues with the driver. There's
> some efficiency cost to it (especially with pasemi_smb_waitready doing
> its polling), but that will be alleviated once the driver receives
> interrupt support.
> 
> Fixes: beb58aa39e6e ("i2c: PA Semi SMBus driver")
> Signed-off-by: Martin Povišer <povik+lin@...ebit.org>

Applied to for-current, thanks!


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