linux-kernel - Re: [PATCHv2 08/16] clk: mvebu: add suspend/resume for gatable clocks

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Message-ID: <20141121095954.5f708f54@free-electrons.com>
Date:	Fri, 21 Nov 2014 09:59:54 +0100
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Mike Turquette <mturquette@...aro.org>
Cc:	"Jason Cooper" <jason@...edaemon.net>,
	"Andrew Lunn" <andrew@...n.ch>,
	"Sebastian Hesselbarth" <sebastian.hesselbarth@...il.com>,
	"Gregory Clement" <gregory.clement@...e-electrons.com>,
	linux-arm-kernel@...ts.infradead.org,
	"Tawfik Bayouk" <tawfik@...vell.com>,
	"Nadav Haklai" <nadavh@...vell.com>,
	"Lior Amsalem" <alior@...vell.com>,
	"Ezequiel Garcia" <ezequiel.garcia@...e-electrons.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 08/16] clk: mvebu: add suspend/resume for gatable
 clocks

Dear Mike Turquette,

On Mon, 17 Nov 2014 14:46:04 -0800, Mike Turquette wrote:
> Quoting Thomas Petazzoni (2014-11-14 07:21:28)
> > This commit adds suspend/resume support for the gatable clock driver
> > used on Marvell EBU platforms. When getting out of suspend, the
> > Marvell EBU platforms go through the bootloader, which re-enables all
> > gatable clocks. However, upon resume, the clock framework will not
> > disable again all gatable clocks that are not used.
> > 
> > Therefore, if the clock driver does not save/restore the state of the
> > gatable clocks, all gatable clocks that are not claimed by any device
> > driver will remain enabled after a resume. This is why this driver
> > saves and restores the state of those clocks.
> 
> It might be a good idea to call clk_disable_unused() from the clk core
> after resuming from suspend.

Yes, this might be an interesting clk core improvement.

> > @@ -177,14 +178,18 @@ struct clk_gating_ctrl {
> >         spinlock_t *lock;
> >         struct clk **gates;
> >         int num_gates;
> > +       struct syscore_ops syscore_ops;
> 
> You are registering suspend/resume ops per clock. Have you considered
> registering a single set of ops for your clock controller driver? See
> drivers/clk/samsung/clk-exynos5420.c for an example.
> 
> Combined with a table of clocks registered by your driver, centralized
> suspend/resume methods might be a cleaner solution.

Ok, I've changed. To be honest, I don't think it makes much change: if
we had two instances of a gatable clock controller, then we would have
two calls to mvebu_clk_gating_setup(), which would register twice the
same syscore_ops. But we were anyway already assuming that we have
already one instance of a gatable clock controller, since the
syscore_ops operation implementation already used a global pointer to
the gatable clock controller.

Will be part of the upcoming v3.

Thanks for the review!

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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