[MIPS] Sibyte: Fix race in sb1250_gettimeoffset().
From Dave Johnson <email@example.com>: sb1250_gettimeoffset() simply reads the current cpu 0 timer remaining value, however once this counter reaches 0 and the interrupt is raised, it immediately resets and begins to count down again. If sb1250_gettimeoffset() is called on cpu 1 via do_gettimeofday() after the timer has reset but prior to cpu 0 processing the interrupt and taking write_seqlock() in timer_interrupt() it will return a full value (or close to it) causing time to jump backwards 1ms. Once cpu 0 handles the interrupt and timer_interrupt() gets far enough along it will jump forward 1ms. Fix this problem by implementing mips_hpt_*() on sb1250 using a spare timer unrelated to the existing periodic interrupt timers. It runs at 1Mhz with a full 23bit counter. This eliminated the custom do_gettimeoffset() for sb1250 and allowed use of the generic fixed_rate_gettimeoffset() using mips_hpt_*() and timerhi/timerlo. Signed-off-by: Ralf Baechle <firstname.lastname@example.org>
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