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!
> 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.
diff --git a/drivers/i2c/busses/i2c-davinci.c
b/drivers/i2c/busses/i2c-davinci.c
index 5795c83..5ddefd6 100644
--- a/drivers/i2c/busses/i2c-davinci.c
+++ b/drivers/i2c/busses/i2c-davinci.c
@@ -283,11 +283,13 @@ static int i2c_davinci_wait_bus_not_busy(struct
davinci_i2c_dev *dev,
& DAVINCI_I2C_STR_BB) {
if (to_cnt <= DAVINCI_I2C_MAX_TRIES) {
if (time_after(jiffies, timeout)) {
- dev_warn(dev->dev,
+ dev_err(dev->dev,
"timeout waiting for bus ready\n");
to_cnt++;
return -ETIMEDOUT;
} else {
+ dev_err(dev->dev,
+ "timeout waiting for bus ready2\n");
to_cnt = 0;
i2c_recover_bus(dev);
i2c_davinci_init(dev);
@@ -381,6 +383,15 @@ i2c_davinci_xfer_msg(struct i2c_adapter *adap, struct
i2c_msg *msg, int sto
dev->adapter.timeout);
if (r == 0) {
dev_err(dev->dev, "controller timed out\n");
+ if(i2c_davinci_wait_bus_not_busy(dev, 1))
+
+ dev_err(dev->dev, "there is really a timeout\n");
+
+ else
+
+ dev_err(dev->dev, "there is no timeout\n");
+
+ }
dev->buf_len = 0;
This is the result:
tps6507x 1-0048: ADC config write failed
i2c_davinci i2c_davinci.1: controller timed out
i2c_davinci i2c_davinci.1: there is no timeout
i2c_davinci i2c_davinci.1: controller timed out
i2c_davinci i2c_davinci.1: there is no timeout
tps6507x 1-0048: TSC mode read failed
i2c_davinci i2c_davinci.1: controller timed out
i2c_davinci i2c_davinci.1: there is no timeout
i2c_davinci i2c_davinci.1: controller timed out
i2c_davinci i2c_davinci.1: there is no timeout
tps6507x 1-0048: TSC mode read failed
...and so on.
> There should be a more elegant way
> to write the loop, but it is too late in the evening to think
> about it :)
>
Perhaps you can help us in the morning, please.
> I doubt if this is related to the errors you guys are seeing,
> but it is worth trying anyway.
>
> Thanks,
> Sekhar
>
Best Regards,
Bastian.
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