Re: [RFC]: Supporting PIO mode of operation in i2c_msg->flags

[Vaibhav Hiremath <vaibhav.hiremath-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On Friday 12 June 2015 05:11 AM, Wolfram Sang wrote:
>> Current implementation:
>> --------------------
>>
>> Everyone probably does have their own custom implementation for this.
>> Or some other mechanism to achieve this (may be hardware support).
>
> Do you have examples? It is easier to look at code.
>

As I mentioned in the "Problem Statement",

I2C interface for PMIC may need to be used at the end of poweroff
sequence where you cannot afford to sleep/schedule, as interrupt has
been disabled.

Earlier I was working on OMAP platform, where I remember we had
implemented something for such requirement, but as I am not in TI
anymore, I can not access the internal code.

Let me check whether I can share the current marvell codebase
outside.


>> /* We can also check i2c_check_functionality(adap,I2C_FUNC_PIO) */
>> 	if (msg->flags & I2C_M_PIO) {
>> 		/* PIO mode operation */
>> 	} else {
>> 		/* non-pio mode of operation */
>> 	}
>
> I'd rather let the core decide. Like introduce a master_xfer_nosleep
> callback and let the core use the standard or the nosleep one. We'd need
> the same for smbus as well.
>
> This leads to the question if we need a M_FLAG or expose the *_nosleep
> functions directly?
>

I thought of it, but did not convince myself after looking at the usage
of this. This function would be used only when interrupt is disabled.


> And I wonder about the demand for it. There are a number of SoCs with
> designated I2C cores for the PMIC which do automated transfers.
>

This is exactly the same reason I did not propose it as a core change.
as I feel that the use of this is very minimal and with M_FLAG driver
can very well handle it.

Thanks,
Vaibhav