Linux/DRA756: Does J6 support I2C stretch feature?

Tao Han

Part Number: DRA756

Tool/software: Linux

Hi expert:

We connect J6 I2c with DS90UH925, the touch panel connect to J6 through DS90UH925/UH926 I2C interface.

The touch panel some time will stop work at 400KHz mode. We find that it maybe have relation ship with I2C stretch feature.

(e2e.ti.com/.../465109)

We find that some engineer has ask Vayu whether support I2C stretch feature but we did not find the confirmed information.

Could you please tell us whether now J6 support I2C stretch feature?

At TRM and dirver at linux kernel/driver/i2c/buses/i2c-omap.c we did not find the work around setting about I2C stretch.

Best Regards!

Han Tao

Below are DS90UB925 engineer provided capture wave at i2C interface, slave device pull SCL low till next bit ready.

over 8 years ago

0 Ravikumar Kattekola over 8 years ago

TI__Expert 4230 points

Hi Tao,

Yes, as per the section 24.1.2.2.10 HS I2C Clock Generation and Synchronization in TRM i2c on DRA75x supports clock stretching. There's no register control over this it's all handled at the bus level in the HW.

Refer to TRM for further details.

Regards,
RK

0 Stanislav Stilyanov over 8 years ago

TI__Mastermind 18400 points

A possible cause could be that corresponding PADCONF register for the CLK pin was not configured with INPUTENABLE=1.

As Ravikumar already said, there is no bit-stretching-enable because it is an i2c standard requirement.

Regards,

Stan

0 Tao Han over 8 years ago in reply to Stanislav Stilyanov

TI__Expert 6435 points

Hi Stan & RK:

Thanks for your suggest and confirm. Looks like excpet clock stretch feature.

The touch panel did not work maybe have another resaon.

We will work with customer to try it. Thanks a lot!

Best Regards!

Han Tao

0 Stanislav Stilyanov over 8 years ago in reply to Tao Han

TI__Mastermind 18400 points

Han Tao,

You can check for INPUTENABLE=1 in the CLK PADCONF register just in case.

Best regards,

Stan

0 Tao Han over 8 years ago in reply to Stanislav Stilyanov

TI__Expert 6435 points

Hi Stan:

I check customer setting INPUT is enable. They connect FPD-link to I2C1 interface.
Looks like I2C configure is right.
Best Regards!
han tao

# in32 0x4a003800
0x4a003800 : 0x00070000
# in32 0x4a003804
0x4a003804 : 0x00070000

0 Stanislav Stilyanov over 8 years ago in reply to Tao Han

TI__Mastermind 18400 points

Right, INPUTENABLE is 1. However, why they decided to use I2C1? It is typically reserved for PMIC, and this could cause some issues. I would recommend other I2C, if possible.

Regards,
Stan

0 Tao Han over 8 years ago in reply to Stanislav Stilyanov

TI__Expert 6435 points

Hi Stan:

Thanks for your suggest about do not use PMIC I2C1 at design.
Now customer find that DS90US925/926 signal D+/D- affect those problem.
Looks like it is not I2C interface affect touch panel no response.
This version of hardware customer can not change the I2C1 connect, we will suggest them change at next version.
Best Regards!
Han Tao

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Linux/DRA756: Does J6 support I2C stretch feature?