linux-kernel - Re: [PATCH v4] i2c: designware: fix __i2c_dw_disable() in case master is holding SCL low

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Message-ID: <ZQn9YtgWKQpUM4od@shikoro>
Date:   Tue, 19 Sep 2023 21:58:26 +0200
From:   Wolfram Sang <wsa@...nel.org>
To:     Yann Sionneau <ysionneau@...ray.eu>
Cc:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jan Dabros <jsd@...ihalf.com>,
        Andi Shyti <andi.shyti@...nel.org>,
        Julian Vetter <jvetter@...rayinc.com>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jonathan Borne <jborne@...ray.eu>
Subject: Re: [PATCH v4] i2c: designware: fix __i2c_dw_disable() in case
 master is holding SCL low

On Mon, Sep 11, 2023 at 04:07:49PM +0200, Yann Sionneau wrote:
> The DesignWare IP can be synthesized with the IC_EMPTYFIFO_HOLD_MASTER_EN
> parameter.
> In this case, when the TX FIFO gets empty and the last command didn't have
> the STOP bit (IC_DATA_CMD[9]), the controller will hold SCL low until
> a new command is pushed into the TX FIFO or the transfer is aborted.
> 
> When the controller is holding SCL low, it cannot be disabled.
> The transfer must first be aborted.
> Also, the bus recovery won't work because SCL is held low by the master.
> 
> Check if the master is holding SCL low in __i2c_dw_disable() before trying
> to disable the controller. If SCL is held low, an abort is initiated.
> When the abort is done, then proceed with disabling the controller.
> 
> This whole situation can happen for instance during SMBus read data block
> if the slave just responds with "byte count == 0".
> This puts the driver in an unrecoverable state, because the controller is
> holding SCL low and the current __i2c_dw_disable() procedure is not
> working. In this situation only a SoC reset can fix the i2c bus.
> 
> Co-developed-by: Jonathan Borne <jborne@...ray.eu>
> Signed-off-by: Jonathan Borne <jborne@...ray.eu>
> Signed-off-by: Yann Sionneau <ysionneau@...ray.eu>

Applied to for-current, thanks!


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