Trying to understand udev

Marvell Orion based
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KeyCat
Posts: 70
Joined: Tue Apr 05, 2011 8:07 am

Trying to understand udev

Post by KeyCat » Thu May 03, 2012 7:46 pm

I tried to make my own udev rules to set a (missing) latency parameter for FTDI USB <-> Serial interface but I'm probably missing something...

First I run udevinfo to get information...

udevinfo -a -p $(udevinfo -q path -n /dev/ttyUSB0)

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  ...
  abbrivated list
  ...
  looking at parent device '/devices/platform/ehci_platform.16781/usb2/2-1':
    KERNELS=="2-1"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{configuration}==""
    ATTRS{serial}=="FTFK232B"
    ATTRS{product}=="USB Serial Converter"
    ATTRS{manufacturer}=="FTDI"
    ATTRS{maxchild}=="0"
    ATTRS{version}==" 1.10"
    ATTRS{devnum}=="2"
    ATTRS{speed}=="12"
    ATTRS{bMaxPacketSize0}=="8"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bDeviceProtocol}=="00"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bDeviceClass}=="00"
    ATTRS{bcdDevice}=="0200"
    ATTRS{idProduct}=="6001"
    ATTRS{idVendor}=="0403"
    ATTRS{bMaxPower}=="100mA"
    ATTRS{bmAttributes}=="a0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bNumInterfaces}==" 1"
    ...


Then according to a howto guide I created a file named "10-local.rules" in /etc/udev/rules.d and tried with following..

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KERNELS=="2-1", SUBSYSTEMS=="usb", ATTRS{manufacturer}=="FTDI", ATTRS{latency_timer}="2"


Then restarted udev but no luck.... udevinfo still shows the same info as listed above and I'm unable to add the "latency_timer" attribute for the FTDI USB <-> Serial interface or am I wrong thinking I can????

According to another guide they mention an easier way to set the latency timer and I tried that first but when entering (as suggested)...

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echo 2 > /sys/bus/usb-serial/devices/ttyUSB0/latency_timer


as root I get back...

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bash: /sys/bus/usb-serial/devices/ttyUSB0/latency_timer: Permission denied


Which I cant figure out either??

/KC

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