On Wed, 13 Oct 2010, Dmitry Shmidt wrote: > On Tue, Oct 12, 2010 at 5:53 PM, Nicolas Pitre <nico@xxxxxxxxxxx> wrote: > >> > Yes, but in this case the suspend methods are inappropriate when the > >> > phone is in live usage. They are meant to be used, say, when the phone > >> > becomes unused and its flap is folded. Otherwise, what is supposed to > >> > happen when you actually want the SDIO card to be suspended if the > >> > suspend method is cut out? > >> > >> "Flap is folded"... It is not the case for usual smartphones anymore. :) > >> Simple scenario - you are siting in chat, wait like 15 sec and your > >> screen goes Off, after another 5 sec kernel gets suspend command and > >> tries to suspend. And you are getting new message - you want to resume > >> quickly and process this packet with no delay. > > > > OK... and how do you want to achieve that? > > > > Why isn't MMC_PM_KEEP_POWER suitable for this? > It just allows to keep power for SDC controller. It doesn't change > suspend/resume behavior from SDIO device > perspective. I think you misunderstood the purpose of MMC_PM_KEEP_POWER. Let's assume the context of a WIFI card. There are cases when you want the WIFI card to be suspended, and some other cases you want it to remain alive when the host CPU does suspend itself. So the decision has to come from the WIFI driver not from the host controller as this is where the information about the device usage is. And that's exactly what MMC_PM_KEEP_POWER is about. When the WIFI driver receives a suspend request, it can set that flag to tell the rest of the stack that it wants to remain alive regardless of what the rest of the system does to go to sleep. Then the firmware on the WIFI card can be notified of that state and go on with its business until it decides it has data for which the host CPU should pay attention. Then the host resumes itself as usual, except for the WIFI driver which simply has to continue operating the card without having to go through reconfiguration, firmware loading, and so on. > >> Maybe what I am describing seems weird, but phone developers are > >> fighting for every mA. > > > > How can you save power when the WIFI interface is not in use if you > > disabled the suspend method with your patch? > You see, we are not talking about wlan chip power. CPU is consuming in > average more energy, so > we are talking about overall savings or consumption and not > specifically wlan. I mean, definitely > turn off SDC controller and remove device will save power, BUT we will > spend much more time on resume > meaning - more power for CPU... I still disagree with your patch. If you want to turn the CPU off and not the peripherals then this is more about some idle state than suspend state. Or at least that's how you should conceptualize it. If some peripherals are not in use, they should always be powered off anyway, whether or not the CPU is suspended. But disabling suspend methods like your patch does is fundamentally the wrong approach. Nicolas
