[v13,2/2] usb: typec: ucsi: add support for Cypress CCGx

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Tue, Oct 23, 2018 at 06:56:59PM +0000, Ajay Gupta wrote:
> > On Wed, Oct 03, 2018 at 11:27:28AM -0700, Ajay Gupta wrote:
> > > Latest NVIDIA GPU cards have a Cypress CCGx Type-C controller over I2C
> > > interface.
> > >
> > > This UCSI I2C driver uses I2C bus driver interface for communicating
> > > with Type-C controller.

> > > +	/*
> > > +	 * Flush CCGx RESPONSE queue by acking interrupts. Above ucsi
> > control
> > > +	 * register write will push response which must be cleared.
> > > +	 */
> > > +	status = ccg_read(uc, CCGX_RAB_INTR_REG, &data, sizeof(data));
> > > +	if (status < 0)
> > > +		return status;

(1)

> > > +	do {
> > > +		status = ccg_write(uc, CCGX_RAB_INTR_REG, &data,
> > sizeof(data));
> > > +		if (status < 0)
> > > +			return status;

(2)

> > > +
> > > +		usleep_range(10000, 11000);
> > > +
> > > +		status = ccg_read(uc, CCGX_RAB_INTR_REG, &data,
> > sizeof(data));
> > > +		if (status < 0)
> > > +			return status;
> > > +	} while ((data != 0x00) && count--);
> > 
> > What's the significance of that count?
> It is like a retry count to clear interrupt status.
> 
> > Shouldn't you return -ETIMEDOUT if count == 0?
> Yes. Good catch. Does the below fix looks ok?

At least for me looks OK (I dunno why I missed that what Heikki found recently).
Nevertheless, I have one more question about (1) and (2) above.

Is it necessary to do one more read before do-while loop?

> 
>         do {
>                 status = ccg_write(uc, CCGX_RAB_INTR_REG, &data, sizeof(data));
>                 if (status < 0)
>                         return status;
> 
>                 usleep_range(10000, 11000);
> 
>                 status = ccg_read(uc, CCGX_RAB_INTR_REG, &data, sizeof(data));
>                 if (status < 0)
>                         return status;
> 
>                 if (!data)
>                         return 0;
>         } while (data && count--);
> 
>         return -ETIMEDOUT;