linux-kernel - Re: [PATCH v6 3/8] ARM: sunxi: Move the clock protection to machine hooks

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Date:	Wed, 23 Apr 2014 15:17:20 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Emilio Lopez <emilio@...pez.com.ar>,
	Dan Williams <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>, devicetree@...r.kernel.org,
	Mike Turquette <mturquette@...aro.org>,
	andriy.shevchenko@...el.com, linux-kernel@...r.kernel.org,
	zhuzhenhua@...winnertech.com, shuge@...winnertech.com,
	linux-sunxi@...glegroups.com, kevin.z.m.zh@...il.com,
	sunny@...winnertech.com, dmaengine@...r.kernel.org
Subject: Re: [PATCH v6 3/8] ARM: sunxi: Move the clock protection to machine
 hooks

On Wed, Apr 23, 2014 at 02:39:02PM +0200, Arnd Bergmann wrote:
> On Thursday 17 April 2014, Maxime Ripard wrote:
> > Since we start to have a lot of clocks to protect, some of them in a few boards
> > only, it becomes difficult to handle the clock protection without having to add
> > per machine exceptions.
> > 
> > Move these where they belong, in the machine definition code.
> > 
> > Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> 
> I don't like the fact that these are required to be hardcoded
> anywhere in source code.

I agree, but that would also mean having a driver for everything that
would need a clock: a CPU, the RAM. I'm not sure we want that either.

> > +#include <linux/clk.h>
> >  #include <linux/init.h>
> >  #include <linux/of_platform.h>
> >  
> > @@ -19,9 +20,17 @@
> >  
> >  static void __init sun4i_dt_init(void)
> >  {
> > +       struct clk *clk;
> > +
> >         sunxi_setup_restart();
> >  
> >         of_platform_populate(NULL, of_default_bus_match_table, NULL, NULL);
> > +
> > +       /* Make sure the clocks we absolutely need are enabled */
> > +       /* DDR clock */
> > +       clk = clk_get(NULL, "pll5_ddr");
> > +       if (!IS_ERR(clk))
> > +               clk_prepare_enable(clk);
> >  }
> 
> Isn't there already DT syntax to do the same? If not, should there be?

I don't think there is, and I gave some thought about it too. But
something a la regulator-always-on wouldn't work with clocks with
multiple outputs (like pll5), because you might need to leave only one
of the output enabled, but not the others, and I couldn't think of a
nice way to do so.

If you have one, I'd be happy to implement it.

Maxime

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

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