linux-kernel - Re: [PATCH v2 06/14] ARM: sun8i: clk: Add clk-factor rate application method

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Message-ID: <20160715081954.GQ4761@lukather>
Date:	Fri, 15 Jul 2016 10:19:54 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Ondřej Jirman <megous@...ous.com>
Cc:	dev@...ux-sunxi.org, linux-arm-kernel@...ts.infradead.org,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Chen-Yu Tsai <wens@...e.org>,
	Emilio López <emilio@...pez.com.ar>,
	"open list:COMMON CLK FRAMEWORK" <linux-clk@...r.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 06/14] ARM: sun8i: clk: Add clk-factor rate
 application method

On Fri, Jul 01, 2016 at 02:53:52AM +0200, Ondřej Jirman wrote:
> On 30.6.2016 22:40, Maxime Ripard wrote:
> > Hi,
> > 
> > On Sat, Jun 25, 2016 at 05:45:03AM +0200, megous@...ous.com wrote:
> >> From: Ondrej Jirman <megous@...ous.com>
> >>
> >> PLL1 on H3 requires special factors application algorithm,
> >> when the rate is changed. This algorithm was extracted
> >> from the arisc code that handles frequency scaling
> >> in the BSP kernel.
> >>
> >> This commit adds optional apply function to
> >> struct factors_data, that can implement non-trivial
> >> factors application method, when necessary.
> >>
> >> Also struct clk_factors_config is extended with position
> >> of the PLL lock flag.
> > 
> > Have you tested the current implementation, and found that it was not
> > working, or did you duplicate the arisc code directly?
> 
> Also of note is that similar code probably doesn't crash in u-boot,
> because there, before changing the PLL1 clock, the cpu is switched to
> 24MHz osc, so it is not overclocked, even if factors align in such a way
> that you'd get the behavior I described in the other email.

That's also something that we can do.

See Meson's clk-cpu clock notifiers for example.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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