[PATCH 0/3] ARM sched_clock selection enhancements

Russell King - ARM Linux linux at arm.linux.org.uk
Tue Mar 12 05:23:58 EDT 2013

On Mon, Mar 11, 2013 at 09:26:34PM -0500, Rob Herring wrote:
> In preparation to move more timer initialization to use CLKSRC_OF and
> out of the platforms, a way to select the timer used for sched_clock is
> needed. This series makes the ARM sched_clock support code prefer 64-bit
> counters or higher frequency counters. This is sufficient at least on
> ARM Ltd boards to use the 24MHz counter rather than sp804 and to always
> use the 64-bit architected timer when present. This mechanism can be
> extended to DT properties if needed for any non-discoverable h/w feature.

No - this stuff is designed specifically to cope with the dilemas of
less-than-64-bit sched_clock sources.  If you have 64-bit sources, then
that should be dealt with differently - this code will break with 64-bit
sources due to the multiplication and shift losing the high order bits.

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