linux-kernel - Re: [PATCH v3 7/7] i2c: bcm2835: Add support for dynamic clock

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Message-ID: <05d1c9d8-644e-a2b1-2853-67b7b77f8509@tronnes.org>
Date:   Thu, 29 Sep 2016 00:10:37 +0200
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Eric Anholt <eric@...olt.net>, wsa@...-dreams.de,
        swarren@...dotorg.org
Cc:     linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 7/7] i2c: bcm2835: Add support for dynamic clock


Den 28.09.2016 23:24, skrev Eric Anholt:
> Noralf Trønnes <noralf@...nnes.org> writes:
>
>> Support a dynamic clock by reading the frequency and setting the
>> divisor in the transfer function instead of during probe.
> Is this fixing some particular case you could note in the commit
> message?  As is, it makes me think that we should be using a notifier
> for when the parent clock (that's the one I assume you're talking about
> being dynamic) changes.  But maybe you're working around a variable VPU
> clock being set by the firmware, because we don't have a notifier for
> it?
>
> I'm a bit worried because I think this is going to be pretty expensive
> to be doing per transfer.

Actually I thought that this was a known problem, but trying to track
it down now, I can't find anything definitive. I don't have any tool
to look at the bus signals, so I couldn't actually test it.
Sorry about this, we can just drop this patch.

Noralf.