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

[Alexander Sverdlin <alexander.sverdlin-xNZwKgViW5gAvxtiuMwx3w@public.gmane.org>]

Hello!

On 18/06/15 11:25, 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.

Ah, beyond the evalboards, there are device-trees not linked into the kernel,
but flashed into the boards, as originally in OF. They are part of the HW, its
description. Not part or description of the Kernel. And you have no way to
introduce this fix any more without updating this OF part if you go with
new compatible property.

>> > 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.

That's true. But I do not have an overview, how many IP versions do you actually have?
I've found one revision in Davinci manual, one revision in Keystone manual, even
including minor revision. Checking only major revision now can survive couple of minor
changes in IP.

-- 
Best regards,
Alexander Sverdlin.