On Thu, 14 Apr 2016, Mathias Nyman wrote: > On 14.04.2016 01:36, Greg KH wrote: > > On Wed, Apr 13, 2016 at 03:21:09PM -0700, Matthew Giassa wrote: > >> The devices support LPM and are USB3.0 certified, and they work fine in > >> Windows using the same Intel 8/9/10 Series USB host controllers, along > >> with Renesas and Fresco controllers. On Linux the devices either seize > >> up or slow down dramatically ever since LPM support was enabled. > > > > Then we need to fix Linux, as it must be our bug. > > > > Mathias, any ideas? > > > > Matthews usbmon log show a flood of LPM related requests that match > something continuously calling usb_disable_lpm() and usb_enable_lpm(). > > I Understood that Matthew uses usbfs (libusb), not uvc. That means > the pm callback in usb_device_pm_ops are used, right? > > usb_runtime_suspend() and usb_runtime_resume() will end up calling > usb_disable_lpm() and usb_enable_lpm() through usb_generic_driver.suspend / resume. > > So I see two possible issues here > > * Unnecessary LPM enabling/ disabling at runtime resume/suspsend > > We should avoid changing LPM values at runtime suspend/resume. The original > motivation for this was that devices can not move from LPM U2 state to U3 directly, > they need to go via U0. Disabling LPM will force the link state to U0, but we do a lot > of request to get this done, both to hub and device (4 at least). > I think this is not a task for the driver. Hub hardware should be able to move the link from U2 > to U0 and finally to U3 on a single Set Port Feature(PORT_LINK_STATE U3) by itself [1]. > > * way too active runtime resuming/suspending using usbfs > It could be possible that runtime suspsend/resume are called way too often when using > usbfs. Not sure if libusb is opening/closing usbfs files all the time, or what triggers it. > I haven't looked into this part yet. Maybe we need a way to prevent autosuspend, or set > autosuspend delay via usbfs Runtime PM already is disabled for any device that is open in usbfs. Unless Matthew's program repeatedly open and closes the device file, the device will remain unsuspended. And indeed, the usbmon file does not show the device getting suspended. As far as I can see, the only other things in the USB stack that disable/enable LPM are: Set-Config, Set-Interface, claim/release_interface. The log file does not show any Set-Config or Set-Interface calls. Matthew, does your program claim and release the interface a lot? This should be necessary only at the start and end of the program. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
