Subject: [PATCH 2/3] ARM: sched_clock: support 64-bit counters

From: [email-masked] (Christopher Covington)
Date: Thu, 21 Mar 2013 10:02:57 -0400

Hi Rob,

On 03/11/2013 10:26 PM, Rob Herring wrote:
> From: Rob Herring <[email-masked]>
> 
> With architected timers, we now have 64-bit counters which can be used
> directly for sched_clock. However, the ARM sched_clock code currently just
> uses the lower 32-bits and handles wrapping in software. Add support for
> using the full 64-bit counter values. If multiple counters are registered,
> a 64-bit counter is preferred.

To be more precise, architected timers are anywhere between 56 and 64 bits
wide, zero-extended to 64-bits. See section B8.1.1 of the ARM ARM rev C.b. I
don't know if the code really needs to change until someone has a need to
distinguish more finely between timers, but if you're using access size as an
approximation for counter width, I feel like it at least deserves a mention in
the comments.

[...]

Regards,
Christopher

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