linux-kernel - Re: [PATCH 01/15] clk: sunxi-ng: Add check for minimal rate to NM PLLs

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Message-ID: <CAGb2v67X8BpvSbxj4So0fdPnY5c6yEKza6b=KZWf7qxMaOUXWg@mail.gmail.com>
Date:   Mon, 26 Feb 2018 18:28:43 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Jernej Skrabec <jernej.skrabec@...l.net>,
        David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH 01/15] clk: sunxi-ng: Add check for minimal rate to NM PLLs

On Mon, Feb 26, 2018 at 6:25 PM, Maxime Ripard
<maxime.ripard@...tlin.com> wrote:
> On Mon, Feb 26, 2018 at 05:43:01PM +0800, Chen-Yu Tsai wrote:
>> On Mon, Feb 26, 2018 at 5:38 PM, Maxime Ripard
>> <maxime.ripard@...tlin.com> wrote:
>> > Hi,
>> >
>> > On Sat, Feb 24, 2018 at 10:45:31PM +0100, Jernej Skrabec wrote:
>> >> Some NM PLLs doesn't work well when their output clock rate is set below
>> >> certain rate.
>> >>
>> >> Add support for that constrain.
>> >
>> > In such a case, you should round the rate to the minimum the clock can
>> > operate at, and not return an error.
>>
>> That's true for round_rate. But what's the expected behavior of set_rate?
>> AFAIK we presume all users call round_rate before set_rate, but that doesn't
>> seem to be true all the time.
>
> One of the first things that happens during a set_rate is a round_rate:
> https://elixir.bootlin.com/linux/v4.16-rc3/source/drivers/clk/clk.c#L1873

Ah! This was added recently in commit ca5e089a32c5 ("clk: use round rate
to bail out early in set_rate").

Thanks for the tip!
ChenYu