Re: [PATCH] usb: host: xhci-tegra: Tegra186/Tegra194 LPM

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On 26.2.2020 10.12, JC Kuo wrote:
> Hi Thierry,
> Yes, it can be verified with a LPM capable device. For example, a VIA USB 3.0
> hub is connected to Jetson-Xavier. "lsusb -v" output [1] shows the device
> supports LPM and the host has enabled U1/U2 states for the device. If host LPM
> is disabled, there will be no "U1 Enabled" and "U2 Enabled" strings in "Device
> Status" section.
> 
> To check LPM operation, disconnect all USB 3.0 devices from the hub and disable
> runtime PM for the super-speed portion of the hub, so that it won't be
> auto-suspended.
> root@tegra-ubuntu:~# echo on > /sys/bus/usb/devices/2-4/power/control
> 
> Since there is no data transaction for the hub, link will enter U2 soon. This
> can be checked by reading XHCI.PORTSC register. In below, PLS (Port Link State)
> field is U2.
> root@tegra-ubuntu:~# devmem 0x3610450
> 0x00001243

A more human friendly way to read portsc registers:

# cat /sys/kernel/debug/usb/xhci/0000\:00\:14.0/ports/port02/portsc 
Powered Connected Enabled Link:U0 PortSpeed:3 Change: Wake: 

-Mathias



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