linux-kernel - Re: [PATCH v3] i2c: designware: fix __i2c_dw_disable() in case master is holding SCL low

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Date:   Wed, 30 Aug 2023 13:42:48 +0300
From:   Jarkko Nikula <jarkko.nikula@...ux.intel.com>
To:     Yann Sionneau <ysionneau@...ray.eu>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Julian Vetter <jvetter@...rayinc.com>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jonathan Borne <jborne@...ray.eu>
Subject: Re: [PATCH v3] i2c: designware: fix __i2c_dw_disable() in case master
 is holding SCL low

Hi

On 8/22/23 12:02, 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>
> ---
> V2 -> V3:
> * do not rename timeout variable for disabling loop
> in order to ease backports
> * replace abort loop with regmap_read_poll_timeout()
> * remove extra empty line.
> 
> V1 -> V2:
> * use reverse christmas tree order for variable declarations
> * use unsigned int type instead of u32 for regmap_read
> * give its own loop to the abort procedure with its own timeout
> * print an error message if the abort never finishes during the timeout
> * rename the timeout variable for the controller disabling loop
> * with the usleep_range(10, 20) it takes only 1 loop iteration.
> Without it takes 75 iterations and with udelay(1) it takes 16
> loop iterations.
> 
>   drivers/i2c/busses/i2c-designware-common.c | 17 +++++++++++++++++
>   drivers/i2c/busses/i2c-designware-core.h   |  3 +++
>   2 files changed, 20 insertions(+)
> 
This doesn't apply against current code. Looks like your base is older 
than v6.2? I.e. before commit 966b7d3c738a ("i2c: designware: Align 
defines in i2c-designware-core.h").

Jarkko