linux-kernel - Re: [PATCH v2 1/1] i2c: aspeed: add proper support fo 24xx clock params

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Message-ID: <CAFd5g45O7rJymFgnWj3SnSKhCvXoX4_xCO8FqeBFCe0-Du9AYg@mail.gmail.com>
Date:   Fri, 28 Jul 2017 17:06:02 -0700
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Rick Altherr <raltherr@...gle.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Joel Stanley <joel@....id.au>,
        Robi Buranyi <rburanyi@...gle.com>,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        linux-i2c@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] i2c: aspeed: add proper support fo 24xx clock params

On Fri, Jul 28, 2017 at 2:00 PM, Rick Altherr <raltherr@...gle.com> wrote:
> Is clk_fractional_divider from include/linux/clk-provider.h appropriate here?
>

Alas, no. clk_fractional_divider is not flexible enough to specify the
divider the
way that it is represented in the Aspeed 24xx/25xx parts which have the divider
expressed as a "base clock" which is always a power of 2 along with the time
where SCL is high and the time that the SCL is low in units of base clock.
Thus, there are two separate "numerator" values and the denominator is
represented as the ilog2 of the actual value.

That being said, I could implement this as a custom clock subclass, which
would probably be cleaner that what I have done.