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

[Ravikumar]

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:
> https://www.youtube.com/watch?v=JdQ21jlwb58
Thanks for sharing the video.
> Regards,
>
>     Wolfram

Regards,
RK