Rajendra Nayak <rnayak@xxxxxx> writes: > Hi Kevin, > > On Saturday 05 November 2011 04:12 AM, Kevin Hilman wrote: >> However, as mentioned previously[1], due to a HW sleepdep between MPU >> and CORE, this constraint isn't actually needed for CORE UARTs, so it's >> a bit wasteful to go through all the constraint setting for no reason. > > I had a short chat with Govind on this and was trying to understand > this better. > Are you referring to the 'autodeps' for omap3 here, because they would > prevent any clock domain from idling as long as MPU or IVA are active, No, I was thinking of HW sleepdeps. However, I looked back at the OMAP3430 TRM and see that MPU does not have a HW sleepdep on CORE like I thought. > but not the other way round. Which means MPU can still idle, while CORE > does not. > > My guess was, its probably the CORE domain idling itself thats causing > the UART sluggishness, (and not MPU idling), due to higher latency, > which is prevented with an active UART module in CORE, but not in PER. OK, that indeed makes sense. Thanks for correcting me. > So Govind did a small experiment to prevent just CORE idling and let MPU > idle alone and that did not show any sluggishness. OK, good. > Now, putting a pm-qos constraint for a UART in CORE still looks > redundant because the latency requirement that UART has is in > some way *indirectly* met (because the active UART in CORE prevents > CORE transitions in idle). > But don't you think the UART driver should express its > latency constraints regardless, without thinking of any indirect ways > in which the same requirements would have already been met? Yes, you're right. The driver should not need to know which powerdomain a given UART is in. It's probably best (and most portable) to have UART always express its requirements all the time. Thanks for digging into this, 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
