[PATCH] at91: i2c-at91: improve time-out handling

[Wolfram Sang]

On Wed, Jan 07, 2015 at 11:31:14AM +0100, Ludovic Desroches wrote:
> Hi Douglas,
> 
> On Thu, Jan 01, 2015 at 01:02:13PM -0500, Douglas Gilbert wrote:
> > With lk 3.19.0-rc2 and a at91sam9g25 (9x5) based system I
> > connected a NXP SC16IS750 I2C to serial bridge. After
> > routing the 750's IRQ back to the sc16is7xx driver and some
> > simple successful test, it was time for some intense testing:
> > Tx looped back to Rx on the 750, open picocom on /dev/ttySC0
> > at 38400, and use hexdump to blast a binary file (in hex) at
> > ttySC0. The I2C SCL speed was 200,000 Hz.
> > 
> > It worked as expected for a few seconds then it wedged the
> > I2C bus. That was repeatable. In the cases that I checked SCL
> > was high, SDA was low (driven by _both_ the G25's macrocell
> > and the 750!!) and IRQ was active (low). This patch stopped
> > the G25 macrocell from driving SDA low in the above wedge
> > (and stopped copious error reports going to the log). I was
> > surprised that a NXP I2C chip got into this situation, IMO
> > SDA on a slave should have a driven low timeout. IMO all
> > I2C master drivers should have provision to drive a gpio
> > connected to a (or all the) slave's RESET line(s).
> > 
> > 
> > ChangeLog:
> >    when handling an I2C bus time-out, first clean-up the
> >    DMA transfer, then do an I2C macrocell software reset
> >    and restore some registers, including the interrupt
> >    mask
> > 
> 
> I am wondering why you need to call at91_twi_irq_save() and
> at91_twi_irq_restore(). The interrupts enabled in the driver are
> AT91_TWI_TXCOMP, AT91_TWI_RXRDY and AT91_TWI_TXRDY and they are managed
> in at91_do_twi_transfer() so they would be set correctly for the next
> transfer.

Douglas, any more info you could provide?

> 
> Regards
> 
> Ludovic
> 
> > Signed-off-by: Douglas Gilbert <dgilbert at interlog.com>
> 
> > diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
> > index 636fd2e..4d78708 100644
> > --- a/drivers/i2c/busses/i2c-at91.c
> > +++ b/drivers/i2c/busses/i2c-at91.c
> > @@ -382,6 +382,7 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
> >  {
> >  	int ret;
> >  	bool has_unre_flag = dev->pdata->has_unre_flag;
> > +	bool timed_out = false;
> >  
> >  	dev_dbg(dev->dev, "transfer: %s %d bytes.\n",
> >  		(dev->msg->flags & I2C_M_RD) ? "read" : "write", dev->buf_len);
> > @@ -440,7 +441,7 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
> >  					     dev->adapter.timeout);
> >  	if (ret == 0) {
> >  		dev_err(dev->dev, "controller timed out\n");
> > -		at91_init_twi_bus(dev);
> > +		timed_out = true;
> >  		ret = -ETIMEDOUT;
> >  		goto error;
> >  	}
> > @@ -471,6 +472,11 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
> >  
> >  error:
> >  	at91_twi_dma_cleanup(dev);
> > +	if (timed_out) {
> > +		at91_twi_irq_save(dev);
> > +		at91_init_twi_bus(dev);
> > +		at91_twi_irq_restore(dev);
> > +	}
> >  	return ret;
> >  }
> >  
> 
> --
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