Hi,
Recently I am writing a program to test the flash card through card
readers with Linux 2.6.12.5. Module usb-storage is used so that I can
open the device "/dev/sdX" to do raw read/write tests. The flash cards
are all of the same capacity. And all the card readers are the same
(VID, PID, serial numbers, etc.). At least two pairs of card/carders are
tested at the same time.
If they are connected to the root hub ports, the tests seem mostly okay.
If a hub is used, they become much easier to fail and /dev/sdX will
become inaccessible ("No such device or address", etc...) although still
present after some long delays. The probability of failure depends on
which hub is used (I think it's a signal quality issue -- PHY issue).
After inspecting the USB bus, I find that the device failed to respond
correctly when this condition happens. For example, it always NAK'ed
when something is wrong. However, the host should be able to do error
recovery. That is, do port reset to recover it.
Kernel 2.6.13 will do better. However, sometimes the I/O operation will
still fail. Then I have to close the file descriptor and reopen the
/dev/sdX to continue testing. Nevertheless, occassionally the I/O
operation will hang there even after all the readers are unplugged.
lsusb will hang also. All accesses to my USB devices hang. A power cycle
of Linux is required to solve this problem so that I can't used Kernel
2.6.13. (The USB system of Kernel 2.6.12 is still possible to hang like
2.6.13. However, the probability seems lower)
I am curious if I can do my user-space error handling. That is, reset
the storage device when /dev/sdX becomes inaccessable with the presence
of usb-storage since some testings of other devices may be still
running? I do a ioctl(fd, IOCTL_USB_RESET, NULL) to
/proc/bus/usb/00X/00X and it succeeds. Howerver, the block device is
still inaccessible. Something when I write the string "running" to
/sys/block/sdX/device/state, the block device will be accessible again.
Is there a formal user-space command sequence to do this kind of job?
Thanks a lot...
Frank Yang
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