linux-kernel - Re: [PATCH 2/2] AT91 slow-clock resume: don't restore the PLL settings when the PLL was off

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Date:	Tue, 13 Apr 2010 10:46:50 +0200
From:	Anders Larsen <al@...rsen.net>
To:	Andrew Victor <avictor.za@...il.com>
Cc:	Julien Langer <julien.langer@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] AT91 slow-clock resume: don't restore the PLL
 settings when the PLL was off

Hi Andrew,

On 2010-04-13 10:14:53, Andrew Victor wrote:
> > +       tst     r3, #(AT91_PMC_MUL &  0xff0000)
> > +       bne     1f
> > +       tst     r3, #(AT91_PMC_MUL & ~0xff0000)
> > +       beq     2f
> > +1:
> >        wait_pllblock
> > +2:
> 
> AT91_PMC_MUL is 11 bits (so 0x7ff0000)

it's not possible to use that constant directly; there are too many bits
set (the ARM instruction set has room for an 8-bit constant and a shift
value)...

> Is the mask (0xff0000) correct in the above code?
> It looks like wait_pllblock will be skipped if the MUL field is set to
> 0x100, 0x200, 0x300, etc.

...so I made the test a two-step process; the first 'tst' checks if
the bits masked by (AT91_PMC_MUL & 0xff0000) = 0x00ff0000 are all zero,
the second 'tst' checks if the bits masked by
(AT91_PMC_MUL & ~0xff0000) = 0x07000000 are zero, so all 11 bits are
indeed tested.

There might well be an easier way to do this, but I didn't manage to
find it - the code isn't on a hot path anyway (it's executed _once_ upon
resume after suspend).

Cheers
Anders

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