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SubjectRe: [RFC 1/1] drivers: i2c: omap: Add slave support

On Thursday 25 August 2016 10:44 PM, Wolfram Sang wrote:
> Hi,
>> The omap i2c controller (at least on dra7x devices)
>> doesn't have start/stop (STT/STP) support for slave mode
>> so event #5 is not implemented in the driver.
> I think you can deduce that. If a new {READ|WRITE}_REQUESTED slave event
> comes in when you had *_PROCESSED events before, there must have been a
> STOP on the bus inbetween.
I've found that the Bus free interrupt can be used for STOP condition in
slave mode.
So this shouldn't be a problem anymore.
>> + if (stat & OMAP_I2C_STAT_XRDY) {
>> + i2c_slave_event(omap->slave, I2C_SLAVE_READ_REQUESTED,
>> + &value);
>> + omap_i2c_write_reg(omap, OMAP_I2C_DATA_REG, value);
>> + i2c_slave_event(omap->slave, I2C_SLAVE_READ_PROCESSED,
>> + &value);
> This looks fishy. READ_REQUESTED is only sent after the address phase.
> Have you read the documentation (Documentation/i2c/slave-interface)?
> Please say if it was unclear.
Will fix this.
>> + /* As of now, We dont need all interrupts be enabled */
>> + omap->iestate = OMAP_I2C_IE_AAS | OMAP_I2C_IE_XRDY | OMAP_I2C_IE_RRDY;
> This looks even more fishy. Are you disabling the master interrupts?
> That's a no (unless there are HW constraints). Your driver should be
> able to switch between master and slave depending on what happens on the
> bus.
Dynamic switching on OMAP I2C IP could be a difficult task.
There is no separate status register for master mode vs slave mode, it's
a common register.
Even the interrupt status bits are reused.

So i cant do a check on status like if(!MSR) slave_irq_handler();

I think instead of status I may need to check the MST(1:master mode,
0:slave mode] bit in I2C_CON
to take a decision on whether to call slave irq_handler or not.
> For more guidance, here is my talk at ELCE 2015:
Thanks for sharing the video.
> Regards,
> Wolfram


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