On 7/1/19 4:52 PM, Greg KH wrote: > On Mon, Jul 01, 2019 at 04:48:48PM +0800, JC Kuo wrote: >> When usb-storage driver detects a UAS capable device, it ignores the >> device if CONFIG_USB_UAS is enabled. usb-storage driver assumes uas >> driver certainly will be loaded. However, it's possible that uas >> driver will not be loaded, for example, uas kernel module is not >> installed properly or it is in modprobe blacklist. >> >> In case of uas driver not being loaded, the UAS capable device will >> not fallback to work at Bulk-only-transfer mode. The device just >> disappears without any notification to user/userspace. >> >> This commit changes usb-storage driver to skip UAS capable device >> only when uas driver is already loaded to make sure the device will >> at least work with Bulk protocol. > > But what happens if the driver is loaded afterward, because 'modprobe' > was called by the driver core (or it should have been, because this is a > device that supports that protocol)? If uas driver is loaded after usb-storage driver probed the device, the device will still work with Bulk-only protocol, though it can't make uses of streams. > > I think you just broke working systems :( > > Why wouldn't the UAS driver get loaded automatically if it is configured > in the system as it is today? An user might want to completely disable uas for some reason so he/she adds "blacklist uas" to modprobe conf file. I think in case of this, usb-storage driver has to enable this device with the legacy Bulk-only protocol instead of ignoring the device. As an alternative to this patch, I thought I could get uas driver loaded before usb-storage driver so I tried moving the functions in drivers/usb/storage/uas-detect.h into uas.c and letting usb-storage links uas_use_uas_driver() of uas.ko. However, that didn't work because uas driver actually depends on usb-storage driver for usb_stor_adjust_quirks(). There will be a recursive dependency. Please let me know if there is better approach to avoid the issue. Thanks, JC > > thanks, > > greg k-h > ----------------------------------------------------------------------------------- This email message is for the sole use of the intended recipient(s) and may contain confidential information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. -----------------------------------------------------------------------------------
