Re: [PATCH v2] i2c: iproc: reset bus after timeout if START_BUSY is stuck

[Jonas Gorski]

Hi,

On Fri, 17 Jul 2026 at 11:40, Mukesh Savaliya
<mukesh.savaliya@xxxxxxxxxxxxxxxx> wrote:
>
>
>
> On 7/17/2026 2:25 PM, Jonas Gorski wrote:
> > If a transaction times out, the START_BUSY signal can stay up, and
> What's exactly START_BUSY signal
> > subsequent transactaction attempts will fail as the bus is still
> transactaction => transaction
> > considered busy.

aah, I was so concentrated on getting the recipients right I forgot to
spell check @_@

> >
> > I can easily trigger this by attempting to read from an address with no
> > device, e.g. when running i2cdetect. After the first read times out, all
> > subsequent read attempts return busy.
> >
> > To get to a working state again, the controller needs to be reset to
> > clear the START_BUSY signal. So check for START_BUSY still asserted on a
> > timeout, and do reset in case it is,
> >
> what's here after it is, ? wanted to end the statement ?

I think I forgot an "it" there, "and do reset it in case it is."

> > This is also done by the original non-upstream iproc-smbus driver
> > implementation [1].
> >
> > Works around situations like:
> >
> >      bcm-iproc-2c 1803b000.i2c: transaction timed out
> >      bcm-iproc-2c 1803b000.i2c: bus is busy
> >      bcm-iproc-2c 1803b000.i2c: bus is busy
> >      bcm-iproc-2c 1803b000.i2c: bus is busy
> >      bcm-iproc-2c 1803b000.i2c: bus is busy
> >      bcm-iproc-2c 1803b000.i2c: bus is busy
> >      ...
> >
> > where the bus never recovers after a timeout.
> isn't there a max retry count ?

In this case it is an already bound driver(s) trying to do (new)
things. Each busy (likely) comes from a new request. In our case there
is an RTC and several SFPs behind an i2c-mux.

So there are two scenarios where I encountered it:

- during runtime after a few hours of uptime, a timeout occurs
accessing an existing device with a bound driver
- and recently while working on a different device I noticed that
reading from an unoccupied address triggers this also

> >
> [...]
> >       if (!time_left && !iproc_i2c->xfer_is_done) {
> > +             /*
> > +              * The controller may fail to clear START_BUSY after a timeout,
> > +              * reset the controller to recover in that case.
> > +              */
> Make it simple ?
> Recover controller if START_BUSY signal is high after timeout

That's more or less what I had in the first version, but was asked to
expand it (split about two short comments)

> > +             if (!!(iproc_i2c_rd_reg(iproc_i2c, M_CMD_OFFSET) &
> > +                    BIT(M_CMD_START_BUSY_SHIFT))) {
> > +                     bcm_iproc_i2c_enable_disable(iproc_i2c, false);
> > +                     bcm_iproc_i2c_init(iproc_i2c);
> > +                     bcm_iproc_i2c_enable_disable(iproc_i2c, true);
> > +             }
> > +
> >               /* flush both TX/RX FIFOs */
> >               val = BIT(M_FIFO_RX_FLUSH_SHIFT) | BIT(M_FIFO_TX_FLUSH_SHIFT);
> >               iproc_i2c_wr_reg(iproc_i2c, M_FIFO_CTRL_OFFSET, val);
>

Best regards,
Jonas

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