Clock register in early init

Turquette, Mike mturquette at
Mon May 21 14:05:57 EDT 2012

On Mon, May 21, 2012 at 1:46 AM, Peter De Schrijver
<pdeschrijver at> wrote:
>> On OMAP I think the only "gotcha" is setting up the timer.  One
>> solution is to open code the register reads and the rate calculation
>> in the timer code.  That is ugly... but it works.
>> > Which advantages do you see in dynamically allocating all this?
>> >
>> There are many but I'll name a couple.  The most significant point is
>> that we can avoid exposing the definition of struct clk if we
>> dynamically allocate stuff.  One can use struct clk_hw_init to
>> statically initialize data, or instead rely on direct calls to
>> clk_register with a bunch of parameters.
> Which means if you make a mistake in specifying parents for example, it will
> only fail at runtime, possibly before any console is active. With static
> initialization, this will fail at compiletime. Much easier to debug.

Is this really a problem?  Once you have good data it does not change.
 Debugging bad data when introducing a new chip is just a fact of
life.  Static versus dynamic is irrelevant here.

>> Another point is that copying the data at registration-time makes
>> __initdata possible.  I haven't done the math yet to see if this
>> really makes a difference.  However if we start doing single zImage's
>> with multiple different ARM SoCs then this could recover some pages.
> On the other hand most clock structures are small, so there will be internal
> fragmentation. Also the arrays of parent clock pointers can be shared between
> different clocks. We have about 70 muxes in Tegra30 and 12 different parent
> arrays.

What is missing from struct clk_hw_init to do what your static arrays do today?


> Cheers,
> Peter.
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> linux-arm-kernel at

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