linux-kernel - Re: [RFC 17/17] clk: zynq: remove call to of_clk

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Message-ID: <d17acba9-85f9-40cd-a176-2005e3e924f8@CO1EHSMHS002.ehs.local>
Date:	Thu, 22 Aug 2013 17:26:47 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
CC:	Mike Turquette <mturquette@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Michal Simek <michal.simek@...inx.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC 17/17] clk: zynq: remove call to of_clk_init

Hi Sebastian,

On Tue, Aug 20, 2013 at 04:04:31AM +0200, Sebastian Hesselbarth wrote:
> With arch/arm calling of_clk_init(NULL) from time_init(), we can now
> remove it from corresponding drivers/clk code.

I think that would break Zynq.
If I see this correctly you call of_clk_init() from common code,
_before_ the SOC specific time init function is called.
The problem is, that we have code setting up a global pointer which is
required by zynq_clk_setup() which is triggered when of_clk_init() is
called.

Let me try to illustrate the current call graph:

time_init()
	zynq_timer_init()		// this machines init_time()
		zynq_slcr_init()	// setup System Level Control Registers including a global pointer
			zynq_clock_init()
				of_clk_init()
					zynq_clk_setup()   // requires pointer setup in zynq_slcr_init()
					...

IIUC, your series would change this to:
time_init()
	of_clk_init()
		zynq_clk_setup()	// SLCR pointer is not setup/NULL
		...
	zynq_timer_init()
		zynq_slcr_init()	// now the pointer becomes valid

	Sören


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