jouni.hogander@xxxxxxxxx (Högander Jouni) writes: > "ext Kevin Hilman" <khilman@xxxxxxxxxx> writes: > >> "Rajendra Nayak" <rnayak@xxxxxx> writes: >> >>>> "Rajendra Nayak" <rnayak@xxxxxx> writes: >>>> >>>> > This patch adds the OMAP3 cpuidle driver. Irq enable/disable is done >>>> > in the core cpuidle driver before it queries the governor for the >>>> > next state. >>>> >>>> Can you explain why you need the IRQ/FIQ disable added to >>>> cpuidle_idle_call() >>>> >>> >>> This was done to prevent any interrupts firing in between a >>> cpuidle_curr_governor->select() and target_state->enter(). >> >> I understand that, but I still don't understand exactly what you're >> trying to prevent. Did you have a specific bug that this prevented? >> >>> An interrupt in between could end up with a previously selected >>> state to be programmed. >> >> Remember that this function _is_ the idle loop, meaning when this runs >> nothing else is happening. After the select, if other system activity >> has happened (e.g. and interrupt, or thread wakeup etc.), it will run >> before the target_state->enter() because of the check for >> need_resched(). > > What happens if this interrupt, or thread wakeup causes change on > latency requirements? Then we are entering sleep state which was > selected using wrong latency requirement data. If a thread is awoken by an interrupt, then need_resched() will be true, and the idle loop will exit without trying to enter the idle state. >> >>> Any suggestions on a better way to handle this? >> >> Just drop the IRQ/FIQ disables altogether. > > At least these are needed at some point in idle loop. Otherwise we > might stepout from idle and sram in a point where it is not acceptable. Agreed, interrupt enable/disable is needed in the idle loop, but not in the CPUidle code. The current OMAP idle loop code (omap2_pm_idle) already does this, but the CPUidle "enter state" hook does not. The omap3_enter_idle() function should be the one who enables/disables interrupts. At a minimulm, the omap_sram_idle should be called with interrupts disabled. Kevin -- 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
