On Saturday, February 18, 2012, huang ying wrote: > On Sat, Feb 18, 2012 at 7:54 AM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > > On Thursday, February 16, 2012, Zhang Rui wrote: > >> On 二, 2012-02-14 at 23:39 +0100, Rafael J. Wysocki wrote: > >> > On Tuesday, February 14, 2012, Zhang Rui wrote: > >> > > On 一, 2012-02-13 at 20:38 +0100, Rafael J. Wysocki wrote: > >> > > > On Monday, February 13, 2012, Alan Stern wrote: > >> > > > > On Mon, 13 Feb 2012, Lin Ming wrote: > [snip] > >> Yeah, I have thought about this for quite a while before, there ARE > >> several ways to do this, but these need a lot of changes in bus code, at > >> least for the buses that support device runtime D3 (off) by ACPI. > >> > >> Lets also take SATA port and ZPODD for example, > >> proposal one, > >> 1) introduce scsi_can_power_off and ata_can_power_off. > >> 2) sr driver set scsi_can_power_off bit and scsi layer is aware of this, > >> thus the scsi host can set this bit as well. > >> 3) in the .runtime_suspend callback of ata port, it knows that its scsi > >> host interface can be powered off, thus it invokes ata_can_power_off to > >> tell the ata layer. > > > > Hmm. I'm not sure why you want to introduce this special "power off" > > condition. In fact, it's nothing special, it only means that the device > > in question shouldn't be accessed by software, which pretty much is equivalent > > to the "suspended" condition (as defined in the runtime PM docs). > > I think some reasons to introduce can_poweroff can be: > > 1) To indicate the implementation of .runtime_suspend/.runtime_resume > is compatible with power off. That is, .runtime_suspend will save all > needed information and .runtime_resume can work on the uninitialized > device. > > If this is already the requirement of > .runtime_suspend/.runtime_resume. Yes, it is. > Then this is not needed. Maybe we > can make that explicitly for these callbacks via some kind of > documentation. I thought it was documented. > 2) To support something like pm-qos. power off device may have more > exit.latency than normal low power state (such as D3Hot). Some device > may disable can_power_off based on that. No, please. There would be totally _no_ _meaning_ of that flag at the core level. Please use subsys_data in struct dev_pm_info for subsystem-specific data (which is this one). > 3) Whether to go to power off should be determined by leaf device > (such as SATA disk), but that may be done by its parent device (such > as SATA port). It's a way for leaf device to tell its parent device > whether it want to go to power off. Well, please see above. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
