Hi Bastian,
On Fri, Mar 18, 2011 at 12:13:31, Bastian.Ruppert@xxxxxxxxxx wrote:
> Dear Sekhar,
>
> >
> > RE: How to put extra clock cycles on i2c cavinci, problems on
> > omapl138 (logic pd som)
> >
> > On Thu, Mar 17, 2011 at 18:55:00, Ben Gardiner wrote:
> >
> > > I noticed on the e2e forums that there is a reason why the PSP uses a
> > > bitbanging i2c interface -- since the 1.0v OPP makes the i2c
> > > controller unusable [1] (I've added Sekhar to the CC since he pointed
> > > out the problem in that post).
> >
> > There was a problem with the way I2C was implemented on the SoM. Here is
> > the information I have for the modifications required on the SoM.
> >
> > "
> > It is likely that the errors seen were a result of the buffer on the
> > I2C clock. The hardware fix for this issue is to remove U24 and
> > R161 and short U24 pins 2 to 4.
> > "
>
> I have a hardware here without this buffer in the I2C clock wire!
Okay. So, I guess the two issues have different root causes.
>
> > There should be an EVM with these fixes already, though I have not
> > tested it myself.
> >
> > Also, recently a bug in the I2C driver was brought to my attention.
> > In the bus busy function:
> >
> > /*
> > * Waiting for bus not busy
> > */
> > static int i2c_davinci_wait_bus_not_busy(struct davinci_i2c_dev *dev,
> > char allow_sleep)
> > {
> > unsigned long timeout;
> > static u16 to_cnt;
> >
> > timeout = jiffies + dev->adapter.timeout;
> > while (davinci_i2c_read_reg(dev, DAVINCI_I2C_STR_REG)
> > & DAVINCI_I2C_STR_BB) {
> > if (to_cnt <= DAVINCI_I2C_MAX_TRIES) {
> > if (time_after(jiffies, timeout)) {
> > dev_warn(dev->dev,
> > "timeout waiting for bus ready\n");
> > to_cnt++;
> > return -ETIMEDOUT;
> > } else {
> > to_cnt = 0;
> > i2c_recover_bus(dev);
> > i2c_davinci_init(dev);
> > }
> > }
> > if (allow_sleep)
> > schedule_timeout(1);
> > }
> >
> > return 0;
> > }
> >
> > If there is a context switch immediately after the while statement,
> > the loop can return a timeout error while there is none. The
> > simple solution would be to check for bus busy again if the
> > timeout condition occurs.
>
> It seems the following patch suggests to your presumption, but
> it is not the solution yet.
Yes, I don't think this bug is the root cause of this issue
either. Ben already tried a fix for this, but it has not
helped him as well.
Thanks,
Sekhar
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