UPDATE: The drivers were temporarily unavailable; they seem to be up again, at least on the Brother US site: http://support.brother.com/g/b/downloadlist.aspx?c=us&lang=en&prod=ds620_all&os=128

I recently bought a Brother DS-620 document scanner that supposedly had support for Linux. It turns out it did, but only after a few quirks. I installed the official Linux drivers, and tried to scan a document using a GUI scanning application. Things were hanging and generally very unresponsive. I checked with the SANE command line tools, e.g. “sane-find-scanner”. It turns out things were indeed working, albeit very slowly. In dmesg I found a lot of messages like:
Jan 29 22:52:13 mchro-laptop kernel: [39172.165644] usb 2-1.3: reset high-speed USB device number 32 using ehci-pci
Jan 29 22:52:13 mchro-laptop kernel: [39172.333832] usb 2-1.3: reset high-speed USB device number 32 using ehci-pci
Jan 29 22:52:13 mchro-laptop kernel: [39172.501677] usb 2-1.3: reset high-speed USB device number 32 using ehci-pci
Jan 29 22:52:13 mchro-laptop kernel: [39172.669712] usb 2-1.3: reset high-speed USB device number 32 using ehci-pci
Jan 29 22:52:13 mchro-laptop kernel: [39172.837679] usb 2-1.3: reset high-speed USB device number 32 using ehci-pci
repeating several times every seconds. At this stage I was thinking that the Linux support was very crappy. After quite a lot of mucking around playing with capturing USB packets using Wireshark, it seemed the device itself was requesting a reset, and the Linux kernel was resetting it approximately 200ms later. Reading some Linux source code, and playing with USB quirks in Linux solved nothing.

Finally, I gave up and booted into Windows to check if the hardware had a defect. In Windows it worked without issues. I upgraded the firmware using the Windows utility to do so. After doing this the scanner worked without issue also in Linux.

So, all in all: There is official Linux support for this scanner, but it seems to require a firmware upgrade. This could definitely be better handled by the Brother documentation.