Re: [RFC PATCH] usb/acpi: Add support usb port power off mechanism for device fixed on the motherboard

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On 2012年05月12日 01:44, Alan Stern wrote:
On Sat, 12 May 2012, Lan Tianyu wrote:

     The power saving depends on devices. I test a usb3.0 ssd. The power saving of
power off is about 2.2w more than just selective suspend. In theory, power
off can help to save remaining power after selective suspend.

That's a lot of power!  Suspended USB devices aren't supposed to
consume more than 2.5 mA of bus current, which at 5 V amounts to<=
0.0125 W.  Does the port really use that much?  Or does the SSD have a
separate power supply that it disables when port power is removed?

The device consumes about 3.1w. The selective suspend can cut down 0.7-0.9w
After power off port, all power will removed.
I test all the motherboard power consumption and get the result.
From lsusb, it's self-powered.

lsusb
Bus 003 Device 006: ID 174c:55aa ASMedia Technology Inc.
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.10
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0
  bDeviceProtocol         0
  bMaxPacketSize0        64
  idVendor           0x174c ASMedia Technology Inc.
  idProduct          0x55aa
  bcdDevice            1.00
  iManufacturer           2 01234567890123456789012345678901234567890123
  iProduct                3 012345678901234567890123456789012345678901234567
  iSerial                 1 0123456789ABCDEF019F
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           32
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          0
    bmAttributes         0xc0
      Self Powered
    MaxPower                0mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass         8 Mass Storage
      bInterfaceSubClass      6 SCSI
      bInterfaceProtocol     80 Bulk (Zip)
      iInterface              0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x02  EP 2 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
Device Status:     0x0001
  Self Powered



--
Best Regards
Tianyu Lan
linux kernel enabling team
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