linux-kernel - Re: [PATCH] ARM: imx: clk-vf610: introduce clks_init

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Date:	Tue, 29 Jul 2014 20:39:20 +0200
From:	Stefan Agner <stefan@...er.ch>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org, shawn.guo@...escale.com,
	kernel@...gutronix.de, peter.chen@...escale.com,
	linux-kernel@...r.kernel.org, jingchang.lu@...escale.com
Subject: Re: [PATCH] ARM: imx: clk-vf610: introduce clks_init_on

Am 2014-07-29 16:44, schrieb Arnd Bergmann:
> On Tuesday 29 July 2014 16:20:28 Stefan Agner wrote:
>> At the end of the boot process, the clock framework might disable
>> required main PLL's. So far, this was no issue since drivers
>> requested clocks, which are descended of the main PLL's (e.g.
>> pll1_pfd1, which provides the system clock).
>>
>> To archive the full 500MHz system clock, DDR clock need to be a
>> descendant of PLL2 rather than PLL1 (DDRC_CLK_SEL set to 0). The
>> bootloader sets up the clocks accordingly before making use of
>> DDR at all. However, in Linux, there is no driver using PLL2,
>> which lead to PLL2 being disabled by the clock framework.
>>
>> With this patch, we make sure that the main system clock and the
>> DDR clock are initially enabled and are kept enabled.
>>
>> Signed-off-by: Stefan Agner <stefan@...er.ch>
>>
> 
> Wouldn't it be better to list this in the DT as a default for
> the respective clocks?
> 

What do you mean by that exactly? Creating a driver for the main PLL's
and add device tree entries to instantiate them, along with a property
like "boot-enabled" or similar?

The approach chosen in this patch is aligned the way it's done for i.MX6
(see arch/arm/mach-imx/clk-imx6q.c). The whole clock module(s) in Vybrid
are slightly striped variants found in i.MX6. For now, I would prefer to
leave it that way. 

--
Stefan
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