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

[Yann Sionneau]

Hi,

On 8/30/23 12:42, Jarkko Nikula wrote:
> 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@xxxxxxxxx>
> > Signed-off-by: Jonathan Borne <jborne@xxxxxxxxx>
> > Signed-off-by: Yann Sionneau <ysionneau@xxxxxxxxx>
> > ---
> > 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").


Oops, I've rebased it on v6.6-rc1 and re-sent it as V4.

Thanks.

Regards,

--

Yann