Hello,
On Thu, Sep 27, 2012 at 11:53:12AM +0200, Sascha Hauer wrote:
> Sounds good. We often have this problem.
>
> I wonder if it's worth to have this as a general callback in the i2c
> layer.
Unfortunately my patch doesn't work. The problem is that if an i2c slave
is stuck with sda low the imx diagnoses a loss of arbitration before
even trying to start pulling SDA low to create a start indication.
So I have to use gpio bitbanging and there is no chance to implement
this in generic code only.
> On Thu, Sep 27, 2012 at 12:56:46AM +0200, Uwe Kleine-König wrote:
> > If an i2c slave pulls SDA low when the SoC wants to start a transfer, it
> > cannot get the bus. This can happen for example if the SoC is reset when
> > it just successfully addressed a slave but before it rises SCL for the
> > slave to ack. Currently this makes the driver refuse to do anything. You
> > can force this situation with the following code assuming you have a
> > device on address 0x50:
> >
BTW, part of the reason I first thought my patch would help is that this
recipe is wrong...
> > /* generate a start condition */
> > gpio_direction_input(I2CSCL);
> > gpio_direction_input(I2CSDA);
> > mdelay(1);
> > gpio_direction_output(I2CSDA, 0);
> >
> > mdelay(1);
> >
> > /* address device 0x50 */
> > for (i = 0; i < 8; ++i) {
> > gpio_direction_output(I2CSCL, 0);
> > mdelay(1);
> > if ((0x50 << 1) >> (7 - i))
... This has to read: if ((0x50 << 1) & (1 << (7 - i))) to actually
stuck the device with address 0x50.
> > gpio_direction_input(I2CSDA);
> > else
> > gpio_direction_output(I2CSDA, 0);
> > mdelay(1);
> > gpio_direction_input(I2CSCL);
> > mdelay(1);
> > }
> > gpio_direction_output(I2CSCL, 0);
> >
> > reset_cpu(0);
> >
(And my bus reset used to help because I asserted that the pinmuxing is
right before the reset but not after this stuck recipe, sigh ⊙_◎.)
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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