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

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Date:   Mon, 26 Feb 2018 11:25:57 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Chen-Yu Tsai <wens@...e.org>
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 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

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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