Re: Power state of USB port on computer reboot
Greg KH gregkh@... writes: On Tue, Apr 09, 2013 at 02:00:51PM +, Blaz Malnersic wrote: Is it possible to influence USB power on OS reboot? Linux and BIOS don't interrupt the power of USB port on reboot, only Windows (all versions we tested do). This along with different times of power lack leads me to conclusion that there is no standard regarding this issue. Also we are dealing with SW+HW, since we only found this issue with Lenovo ThinkPads. As you are having problems with Windows, not Linux, why are you asking this on a Linux mailing list? Please just file a bug with Windows if this is a needed thing for your systems (hint, you can never rely on USB power being present across a reboot, that's an undefined system state, sorry.) good luck, greg k-h -- To unsubscribe from this list: send the line unsubscribe linux-usb in the body of a message to majordomo@... More majordomo info at http://vger.kernel.org/majordomo-info.html Hi, :) I am trying with Lenovo and Microsoft but there is not much happening from their side. If it is as you said concerning the undefined state of the USB power across a reboot, that information is very helpful for me. It means we have to design things differently (apart from the obvious one which is to replace the notebooks...). How come this is undefined? Best regards, Blaz P.S. This is why I love Linux community - open exchange of knowledge. I am not saying it is not happening in MS/commercial world... -- To unsubscribe from this list: send the line unsubscribe linux-usb in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Power state of USB port on computer reboot
Hi, subject: Power supply interrupted on USB port (normal and Always-on) when performing reboot from any Windows version but not when rebooting from Linux or BIOS (Lenovo ThinkPad T4xx). Why the difference? According to my research there is no standard describing the power state (power on/power off) of USB port on computer reboot. Is that really so? The problem we are having is the following. We have external hardware VPN device which is powered through USB port. In order to establish VPN, one must access web page on the device and enter password. To be able to log-in to domain and apply Computer Configuration part of Group Policy assigned through AD, one must first log-in (offline, cached mode), establish VPN tunnel, perform OS reboot and log-in to domain. Since the device is USB powered it is mandatory that there is no interruption of power supply during this procedure. On Dell laptops (several models) and Apple Mac Books Pros this works perfectly. However, on Lenovo ThinkPad (tested T410 and T420), the USB power supply is interrupted during Windows OS reboot. Strangely it is not interrupted when performing reboot in Linux or when still in POST/BIOS mode. Another strange thing is that power supply is interrupted for different periods of time. T410 WinXP 225ms (525ms), T410 Win7x86 25ms(350ms), T410 Win7x64 75ms (350ms), T410 Win8 1050ms (1350ms), T420 Win7x86 5ms. The values in parenthesis denote measurements on Allways-On USB port. Is it possible to influence USB power on OS reboot? Linux and BIOS don't interrupt the power of USB port on reboot, only Windows (all versions we tested do). This along with different times of power lack leads me to conclusion that there is no standard regarding this issue. Also we are dealing with SW+HW, since we only found this issue with Lenovo ThinkPads. Blaz Malnersic -- To unsubscribe from this list: send the line unsubscribe linux-usb in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
