Re: [PATCH] i2c: davinci: Fix bus rate calculation on Keystone SoC

[Sekhar Nori <nsekhar-l0cyMroinI0@public.gmane.org>]

Hi Alexander,

On Thursday 18 June 2015 02:39 PM, Alexander Sverdlin wrote:
> Hi!
> 
> On 18/06/15 11:00, ext Sekhar Nori wrote:
>>> +	if (davinci_i2c_read_reg(dev, DAVINCI_I2C_ICPID2_REG) == 0x2206) {
>>>> +		dev_dbg(dev->dev, "Keystone SoC detected\n");
>>>> +		d = 6;
>>>> +	}
>> I think its better to use a different compatible string for i2c on
>> keystone devices rather than using a fixed hardcoded IP version.
> 
> Yeah, this should have been done from the beginning, when the driver has been
> re-used for Keystone, but this time is already missed, so I don't want
> to introduce huge incompatibility with the existing device-trees.

How is backward compatibility broken? compatible property is a list, so
you would do something like:

	compatible = "ti,keystone-i2c", "ti,davinci-i2c";

Newer kernels would keep working with older device tree blobs. Older
kernels wont have the fix, but thats true even now.

> And from the other PoV, device-trees are for something one cannot probe. We
> can probe for Keystone revisions and can free the end-user from this headache
> completely.

Keep in mind that this can invite driver patching whenever version
number is tinkered with in hardware - even for otherwise
software-invsible changes.

Thanks,
Sekhar