On Tue, 19 Nov 2019, Ikjoon Jang wrote: > On Sun, Nov 17, 2019 at 11:46 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Sun, 17 Nov 2019, Ikjoon Jang wrote: > > > > > This patchset enables hard wired hub device to use different bInterval > > > from its descriptor when the hub has a combined device node. > > > > > > When we know the specific hard wired hub supports changing its polling > > > interval, we can adjust hub's interval to reduce the time of waking up > > > from autosuspend or connect detection of HIDs. > > > > In fact, _all_ hubs support changing the polling interval. The value > > given in the USB spec is just an upper limit; any smaller value is > > equally acceptable. > > > > So why are you doing this only for hard-wired hubs? Why not for all > > hubs? > > Because we only want to apply it to a specific device instance under > our control. Why? What's so special about that device instance? For example, why not instead have a poll_interval sysfs attribute for all hubs that can be written from userspace? Then people could reduce the autoresume latency for any device they want. > We apply autosuspend to built-in touchpad device for power savings, > > Users can attach external hub devices with same VID:PID that we don't want to > change the behavior. Why don't you want to change the behavior? Or allow the user to change the behavior? > Maybe disabling autosuspend for external HIDs > can be more reasonable for that case? If it makes sense to to save power for your built-in touchpad device, why doesn't it also make sense to save power for other external HIDs? > > And is 250 ms really too long to wait for remote wakeup or connect > > detection? What's the real motivation behind this change? > > When a user starts to move the cursor while touchpad is in autosuspend state, > It takes more than >250ms (worst case can be >500ms) to wake up and response. > That makes the cursor stuck for a while and warp to another location suddenly. All right, that's a good reason. But doesn't it apply just as well to other devices, not only your built-in touchpad? Alan Stern
