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

From: Sekhar Nori <nsekhar-l0cyMroinI0@public.gmane.org>
To: Alexander Sverdlin
	<alexander.sverdlin-xNZwKgViW5gAvxtiuMwx3w@public.gmane.org>,
	Kevin Hilman
	<khilman-1D3HCaltpLuhEniVeURVKkEOCMrvLtNR@public.gmane.org>,
	Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>,
	linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Murali Karicheri <m-karicheri2-l0cyMroinI0@public.gmane.org>
Subject: Re: [PATCH] i2c: davinci: Fix bus rate calculation on Keystone SoC
Date: Thu, 18 Jun 2015 16:42:47 +0530	[thread overview]
Message-ID: <5582A7AF.5030000@ti.com> (raw)
In-Reply-To: <558297B3.2060406-xNZwKgViW5gAvxtiuMwx3w@public.gmane.org>

On Thursday 18 June 2015 03:34 PM, Alexander Sverdlin wrote:
> Hi!
> 
> On 18/06/15 11:47, ext Sekhar Nori wrote:
>>> 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.
>> I see. So how critical is this fix? That should be described in the
>> commit description. And if its really critical, stable kernel should be
>> CCed too.
> 
> Now we got to the point, see below...
> 
>>>>>>>>>> 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.
>> Yeah, sticking to major version should help. What I am worried about are
>> versions coming in future, not those existing. And development on
>> keystone architecture is ongoing in TI.
> 
> This is not really critical fix. Currently bus rate is lower than expected because of these
> calculation errors. The fix maximizes the bus rate. So newer SoCs will run little bit slower
> until support is added to this part of the code. Not really critical. So no point in CCing
> stable maintainers also.

If its not a critical fix, do we really need to care about older DTBs
which have been ROM'ed into production?

Thanks,
Sekhar