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Date:   Fri, 15 Apr 2022 23:12:28 +0200
From:   Wolfram Sang <wsa@kernel.org>
To:     Martin =?utf-8?Q?Povi=C5=A1er?= <povik+lin@cutebit.org>
Cc:     Hector Martin <marcan@marcan.st>, Sven Peter <sven@svenpeter.dev>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Alyssa Rosenzweig <alyssa@rosenzweig.io>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Jean Delvare <khali@linux-fr.org>,
        Olof Johansson <olof@lixom.net>,
        linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, linux-i2c@vger.kernel.org,
        linux-kernel@vger.kernel.org, Janne Grunau <j@jannau.net>
Subject: Re: [PATCH] i2c: pasemi: Wait for write xfers to finish
Message-ID: <YlnfvJDyluEDfu39@shikoro>
Mail-Followup-To: Wolfram Sang <wsa@kernel.org>,
        Martin =?utf-8?Q?Povi=C5=A1er?= <povik+lin@cutebit.org>,
        Hector Martin <marcan@marcan.st>, Sven Peter <sven@svenpeter.dev>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Alyssa Rosenzweig <alyssa@rosenzweig.io>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Jean Delvare <khali@linux-fr.org>, Olof Johansson <olof@lixom.net>,
        linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org,
        linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
        Janne Grunau <j@jannau.net>
References: <20220329183817.21656-1-povik+lin@cutebit.org>
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On Tue, Mar 29, 2022 at 08:38:17PM +0200, Martin Povi=C5=A1er 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:
>=20
>  * Driver doesn't check for FIFO space.
>=20
>  * 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.
>=20
> 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.
>=20
> Fixes: beb58aa39e6e ("i2c: PA Semi SMBus driver")
> Signed-off-by: Martin Povi=C5=A1er <povik+lin@cutebit.org>

Applied to for-current, thanks!


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