On Wed, Jul 13, 2011 at 8:29 PM, Kevin Hilman <khilman@xxxxxx> wrote: > "Dong, Chuanxiao" <chuanxiao.dong@xxxxxxxxx> writes: > > [...] > >>> >>> Basially, the question is: can the driver be reworked such that a system >>> suspend does not need to runtime resume the device? For most devices, >>> we kind of expect that if the device is runtime suspended, a system >>> suspend will have nothing extra to do, but this driver runtime resumes >>> the device during system suspend in order to do "stuff", which I >>> admitedly don't fully undestand. >>> >>> Ideally, the "stuff" needed for runtime suspend and system suspend could >>> be made to be common such that a system suspend of a runtime suspended >>> device would be a noop. >>> >>> Is this possible? >>> >>> Kevin >> >> During system suspended patch, a callback named .prepare will be first >> done before .suspend is called, and .complete callback will be called >> after .resume is called. These two callbacks are in pair. If driver >> can implement the .prepare and hold the usage count in this callback, >> then runtime pm suspend/resume will not happen during device >> suspending. So there will be no need to add pm_runtime_get* and >> pm_runtime_put* in .suspend/.resume. > > That doesn't avoid the problem, since the device is still runtime > resumed and then re-suspended during system suspend. > > My basic question is this: why does this device need to be runtime > resumed during system suspend? Why can't it just stay runtime > suspended? > >From my understanding, the runtime suspend is usually implemented to not lose the card 'context', i.e. transactions can continue after a runtime suspend / resume cycle. For system suspend, the MMC core sends a sleep command (which, in itself, is a transaction) to the card to go to sleep state, and for all practical purposes, the card is treated as 'removed'. When the system resumes, the card is rescanned and re-initialized. Hence, for system suspend, the MMC controller needs to be enabled to actually send the command which puts the card to sleep (and hence the resume). Best regards, Venkat. -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
