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Loongson2 cpu_wait function

DISCUSSION Ralf Baechle 2 participants 2 messages May 23, 2013 MIPS

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Ralf Baechle

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During the 3.10 merge cycle many MIPS platforms were broken by the generic idle loop patches. A patch series to fix this has already been merged but I'm wondering if fb40bc3e94933007d3e42e96daf1ec8044821cb8 [MIPS: Idle: Re-enable irqs at the end of r3081, au1k and loongson2 cpu_wait.] is sufficient and correct for Loongson 2.

In particular:

o drivers/cpufreq/loongson2_cpufreq.c protects accesses to LOONGSON_CHIPCFG0 in loongson2_cpu_wait with a spinlock. This spinlock is not used anywhere else in the kernel so it would appear there is still a race with other accesses to LOONGSON_CHIPCFG0.
o It's not SMPly correct - even if cpufreq_exit restores the old value of cpu_wait on a SMP system another processor might still be executing loongson2_cpu_wait().
o I'd appreciate if at least some basic power saving would be used even if CONFIG_LOONGSON2_CPUFREQ was disabled, that is loongson2_cpu_wait should go back to arch/mips/kernel/idle.c.
o Could somebody test if Loongson 2 is working? Thanks!

Ralf

#1 lore raw

Hi,

Quoted 8 lines · Ralf Baechle

During the 3.10 merge cycle many MIPS platforms were broken by the generic idle loop patches. A patch series to fix this has already been merged but I'm wondering if fb40bc3e94933007d3e42e96daf1ec8044821cb8 [MIPS: Idle: Re-enable irqs at the end of r3081, au1k and loongson2 cpu_wait.] is sufficient and correct for Loongson 2.

In particular:

Quoted 7 lines

o drivers/cpufreq/loongson2_cpufreq.c protects accesses to LOONGSON_CHIPCFG0 in loongson2_cpu_wait with a spinlock. This spinlock is not used anywhere else in the kernel so it would appear there is still a race with other accesses to LOONGSON_CHIPCFG0.
o It's not SMPly correct - even if cpufreq_exit restores the old value of cpu_wait on a SMP system another processor might still be executing loongson2_cpu_wait().

I think Loongson2 is UP-only?

Quoted 4 lines

o I'd appreciate if at least some basic power saving would be used even if CONFIG_LOONGSON2_CPUFREQ was disabled, that is loongson2_cpu_wait should go back to arch/mips/kernel/idle.c.
o Could somebody test if Loongson 2 is working? Thanks!

It works (tested d97955625710b57f24427e403f150126078273c2), but cpufreq seems to be broken for some reason:

[    6.136000] calling  cpufreq_init+0x0/0x8c @ 1
[    6.140000] cpufreq: Loongson-2F CPU frequency driver.
[    6.144000] initcall cpufreq_init+0x0/0x8c returned -19 after 4000 usecs

I would also like to remind that the boot is still unreliable without this patch: http://patchwork.linux-mips.org/patch/4958/

A.