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

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Hi Mathias,
Thanks for the tip. It's really helpful.

root@tegra-ubuntu:/d/usb/xhci/3610000.usb/ports/port04# cat portsc
Powered Connected Enabled Link:U2 PortSpeed:4 Change: Wake:

-JC

On 2/26/20 5:32 PM, Mathias Nyman wrote:
> 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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