________________________________________ From: Daniel Lezcano [daniel.lezcano@xxxxxxxxxx] Sent: Wednesday, September 17, 2014 8:22 PM To: Shilimkar, Santosh; Menon, Nishanth; Tony Lindgren; Kristo, Tero; Paul Walmsley Cc: Kevin Hilman; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-omap@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; J, KEERTHY; Benoît Cousson Subject: Re: [PATCH 08/10] ARM: OMAP5/DRA7: PM: cpuidle MPU CSWR support On 09/17/2014 04:20 PM, Shilimkar, Santosh wrote: > Sorry for the format. Emailing from webmail. > ________________________________________ [ ... ] >> + cx->mpu_state_vote++; >> + if (cx->mpu_state_vote == num_online_cpus()) { >> + pwrdm_set_logic_retst(mpu_pd, cx->mpu_logic_state); >> + omap_set_pwrdm_state(mpu_pd, cx->mpu_state); >> + } >> + raw_spin_unlock_irqrestore(&mpu_lock, flag); >> + >> + omap4_enter_lowpower(dev->cpu, cx->cpu_state); >> + >> + raw_spin_lock_irqsave(&mpu_lock, flag); >> + if (cx->mpu_state_vote == num_online_cpus()) >> + omap_set_pwrdm_state(mpu_pd, PWRDM_POWER_ON); >> + cx->mpu_state_vote--; >> + raw_spin_unlock_irqrestore(&mpu_lock, flag); > > I am not sure that will work. What happens if a cpu exits idle and then > re-enter idle immediately ? > > [Santosh] It works and that case is already taken care. CPU exist the idle and then votes > out for cluster state and if it reenters with the right targeted state, the cluster state would > be picked. It isn't possible to have one cpu disabling the coherency, while the other one is looking for a lock ? Or eg. cpu0 is on WFI then cpu1 is the last entering idle. While cpu1 is entering 'lowpower', cpu0 exits the wfi check the state vote and set the power domain on. In the meantime cpu1 disables the coherency and cpu0 decrease the vote and release the lock. Could be possible there is a very small racy window here ? [Santosh] The coherency isn't disable by CPU. Thats actually taken care by hardware. CPU takes it own power domain down and takes itself out of coherency. The Coherency is always ON as long as there is a CPU ON and SMP bit on that CPU is enabled. The scenario, you mentioned can never happen on this hardware thanks to the inbuilt smart hardware. If you have more questions, lets discuss. I am around here at connect. ;-) Regards, Santosh-- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html