AM3352: Cannot enable I2C test mode (via I2C_SYSTEST) in Linux kernel module

Leffe Brune

Part Number: AM3352
Other Parts Discussed in Thread: AMIC110

Hello there!

We are trying to enable I2C test mode as described in section 21.4.1.25 of "AM335x and AMIC110 Sitara™ Processors Technical Reference Manual".

Here is our code:

        omap_i2c_write_reg(_dev, OMAP_I2C_CON_REG, OMAP_I2C_CON_EN);
        dev_info(_dev->dev, "Going to write SYSTEST");
        omap_i2c_write_reg(omap_i2c_test_dev, OMAP_I2C_SYSTEST_REG, reg);
        dev_info(_dev->dev, "Wrote SYSTEST : 0x%08x", reg);
        dev_info(_dev->dev, "Going to read SYSTEST");
        reg = omap_i2c_read_reg(_dev, OMAP_I2C_SYSTEST_REG);
        dev_info(_dev->dev, "SYSTEST is 0x%08x", reg);

The value we are trying to write is 0x0000f001.

Unfortunately, the read always returns value 0x000001e0 which indicates no test mode has been enabled.

[ 318.074813] omap_i2c 4819c000.i2c: Going to write SYSTEST
[ 318.080545] omap_i2c 4819c000.i2c: Wrote SYSTEST : 0x0000f001
[ 318.086557] omap_i2c 4819c000.i2c: Going to read SYSTEST
[ 318.092112] omap_i2c 4819c000.i2c: SYSTEST is 0x000001e0

What is the correct flow to enable I2C test mode?

over 6 years ago

0 Nick Saulnier over 6 years ago

TI__Guru** 101750 points

Hello Leffe,

What version of Linux are you running?

Regards,

Nick

0 Leffe Brune over 6 years ago in reply to Nick Saulnier

Prodigy 40 points

Hi Nick,
We are using a custom buildroot based on Linux with kernel 3.8.13

0 Leffe Brune over 6 years ago in reply to Nick Saulnier

Prodigy 40 points

Further investigation showed we are able to write I2C_SYSTEST register for Sitara I2C bus 2 (which is enumerated as bus 1 by Linux kernel because Sitara I2C bus is disabled by dts configuration).

Can anybody help understand the difference in behavior we see?

Thanks in advance!

0 Nick Saulnier over 6 years ago in reply to Leffe Brune

TI__Guru** 101750 points

Hello Leffe,

Please provide more information about "the difference in behavior we see".

1) Are you saying that you are not able to write to the SYSTEST register of the I2C that has been disabled in Linux, but you can write to the SYSTEST register of the enabled I2C? Or are you saying something else?

2) Did you use the exact same code for both results, or did you change something?

3) Are there any other differences between the two behaviors you are observing?

Regards,
Nick

0 Leffe Brune over 6 years ago in reply to Nick Saulnier

Prodigy 40 points

Hi Nick,

We have two enabled I2C buses in our system - bus 0 and bus 1.
We would like to write SYSTEST register on bus 0 but it fails as described above. However, exactly the same write operation (and same code) succeeds on bus 1.

0 Nick Saulnier over 6 years ago in reply to Leffe Brune

TI__Guru** 101750 points

Hello Leffe,

I am sorry for the delayed response. I have not yet found anyone on this end who has much experience with SYSTEST, so I am not sure if this is a vestigial part of the IP that was inherited from some previous processor, or if it is just not commonly used. It should work the same on all active instances of I2C, however.

Did you resolve the issue, or do you need additional assistance?

Regards,
Nick

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AM3352: Cannot enable I2C test mode (via I2C_SYSTEST) in Linux kernel module