On Sat, 10 Jul 2010, Sarah Sharp wrote: > (I recently found this patch languishing in my git tree. I've updated it > to 2.6.35-rc4, but I haven't retested it.) > > A while back, Oliver Neukum made a patch to suspend mass storage devices > between SCSI commands. This patch uses some of the work from Oliver's > patch. > > Unfortunately, Oliver's patch made SD readers lose their minds. After a > suspend, all previous internal state is lost and they can't tell > whether a card had been recently inserted or removed. After a suspend, > the first TEST_UNIT_READY command sent to an SD card reader will report > "Media may have changed", and the next TEST_UNIT_READY command will report > actual media presence or removal. If the SD readers are suspended between > TEST_UNIT_READY commands, they will continually report "Media may have > changed", and no media change will ever be detected. > > Disable autosuspend for a mass storage device until we know medium is not > present, by peeking into the results of a TEST_UNIT_READY command. I > matched against the key, asc, and ascq fields, but I believe I only really > need to match the asc and asq fields. > > This patch is only useful if the autosuspend timeout is set to 0 seconds > (an immediate suspend). You can generate the udev rule to enable > autosuspend and set the timeout with my usb-pm tool script > (vid-pid-to-udev-rule.sh) at http://git.moblin.org/cgit.cgi/usb-pm-tool/ > > This patch would be even more useful if we could get userspace to stop > polling for new media so often. > > This patch works fine with empty SD card readers. Some thumb drives > will also autosuspend when they are unmounted or ejected from the Gnome > filesystem GUI. Other thumb drives always report "Medium may have > changed" if they need to flash stupid LEDs, like the original Linux > Plumbers Conference thumb drive. I would prefer not to have this accepted. There already are patches waiting in James Bottomley's queue to add runtime PM support to the SCSI subsystem; once they are merged, adding autosuspend to usb-storage will be a 4-line change -- already written and tested. (Unfortunately James is very bad about letting people know the status of pending patches. I have no idea when these will be merged or even if he is willing to accept them.) Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
