linux-kernel - Re: [PATCH 1/2] clk: ingenic: Fix round_rate misbehaving with non-integer dividers

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Message-ID: <155085944882.77512.7360345623017019976@swboyd.mtv.corp.google.com>
Date:   Fri, 22 Feb 2019 10:17:28 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Paul Cercueil <paul@...pouillou.net>
Cc:     Maarten ter Huurne <maarten@...ewalker.org>,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paul Cercueil <paul@...pouillou.net>, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] clk: ingenic: Fix round_rate misbehaving with non-integer dividers

Quoting Paul Cercueil (2019-01-27 18:09:20)
> Take a parent rate of 180 MHz, and a requested rate of 4.285715 MHz.
> This results in a theorical divider of 41.999993 which is then rounded
> up to 42. The .round_rate function would then return (180 MHz / 42) as
> the clock, rounded down, so 4.285714 MHz.
> 
> Calling clk_set_rate on 4.285714 MHz would round the rate again, and
> give a theorical divider of 42,0000028, now rounded up to 43, and the
> rate returned would be (180 MHz / 43) which is 4.186046 MHz, aka. not
> what we requested.
> 
> Fix this by rounding up the divisions.
> 
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> Tested-by: Maarten ter Huurne <maarten@...ewalker.org>
> Cc: <stable@...r.kernel.org>
> ---

Applied to clk-next