On Thu, 15 May 2014, Jacob Pan wrote: > On Thu, 15 May 2014 10:29:42 -0400 (EDT) > Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > On Thu, 15 May 2014, Jacob Pan wrote: > > > > > > > should we respect ignore_children flag here? not all parent > > > > > devices create children with proper .prepare() function. this > > > > > allows parents override children. > > > > > I am looking at USB, a USB device could have logical children > > > > > such as ep_xx, they don't go through the same > > > > > subsystem .prepare(). > > > > > > > > Well, I'm not sure about that. Let me consider that for a while. > > > OK. let me be more clear about the situation i see in USB. Correct > > > me if I am wrong, a USB device will always has at least one > > > endpoint/ep_00 as a kid for control pipe, it is a logical device. > > > So when device_prepare() is called, its call back is NULL which > > > makes .direct_complete = 0. Since children device suspend is called > > > before parents, the parents .direct_complete flag will always get > > > cleared. > > > > > > What i am trying to achieve here is to see if we avoid resuming > > > built-in (hardwired connect_type) non-hub USB devices based on this > > > new patchset. E.g. we don't want to resume/suspend USB camera every > > > time in system suspend/resume cycle if they are already rpm > > > suspended. We can save ~100ms resume time for the devices we have > > > tested. > > > > This is a good point, but I don't think it is at all related to > > ignore_children. > > > > Instead, it seems that the best way to solve it would be to add a > > ->prepare() handler for usb_ep_device_type that would always turn > > on direct_complete. > > > yeah, that would solve the problem with EP device type. But what about > other subdevices. e.g. for USB camera, uvcvideo device? We can add > .prepare(return 1;) for each level but would it be better to have a > flag similar to ignore_children if not ignore_children itself. Something like that could always be added. > Actually, I don't understand why this is not related to > ignore_children. Could you explain? It's hard to explain why two things are totally separate. Much better for you to describe why you think they _are_ related, so that I can explain how you are wrong. > If the parent knows it can ignore children and already rpm suspended, > why do we still ask children? The "ignore_children" flag doesn't mean that the parent can ignore its children. It means that the PM core is allowed to do a runtime suspend of the parent while leaving the children at full power. In particular, it doesn't mean that the children's ->suspend() callback will work correctly if it is called while the parent is runtime suspended. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
