On Fri, Mar 05, 2021 at 05:54:43PM +0100, Matthias Schwarzott wrote: > Hi folks, > > I have an issue with my Amazon Kindle. Since some time the device > disconnects 2 seconds after a sync command sent via USB. > > See also this matching bug report: > https://bugzilla.kernel.org/show_bug.cgi?id=203973 > > My current workaround is this udev-rule: > SUBSYSTEM=="block", ACTION=="add", ENV{DEVTYPE}=="disk", > ENV{ID_VENDOR}=="Kindle", RUN+="/bin/bash -c 'echo write\ through > > /sys/block/%k/queue/write_cache'" > > But I like to find a proper solution. > > I did various recordings of usb-traffic with wireshark on linux and windows. > > On windows, the device does not disconnect after the "Synchronize Cache" > command. > > One major difference I noticed looking at service answer time statistics: > Windows sends a lot more requests of type "Test Unit Ready". > * Windows: 6385 calls > * linux: 71 calls It's generally well known that Windows issues lots and lots of redundant commands to USB storage drives. > After most of the "Synchronize Cache" commands on windows there was directly > a following "WRITE" command. It seems WRITE commands avoid the disconnect. > > But sending a plain "Synchronize Cache" under windows (8.1 and 10) does not > trigger the disconnect. > > Windows: > 1583 14.891478 host 1.6.1 USBMS 58 SCSI: Synchronize Cache(10) LUN: 0x00 > (LBA: 0x00000000, Len: 0) > 1584 14.891595 1.6.1 host USB 27 URB_BULK out > 1585 14.891613 host 1.6.1 USB 27 URB_BULK in > 1586 14.896866 1.6.1 host USBMS 40 SCSI: Response LUN: 0x00 (Synchronize > Cache(10)) (Good) > 1589 15.687209 host 1.6.1 USBMS 58 SCSI: Test Unit Ready LUN: 0x00 > 1590 15.687353 1.6.1 host USB 27 URB_BULK out > 1591 15.687358 host 1.6.1 USB 27 URB_BULK in > 1592 15.687405 1.6.1 host USBMS 40 SCSI: Response LUN: 0x00 (Test Unit > Ready) (Good) > 1713 16.699689 host 1.6.1 USBMS 58 SCSI: Test Unit Ready LUN: 0x00 > 1714 16.699820 1.6.1 host USB 27 URB_BULK out > 1715 16.699825 host 1.6.1 USB 27 URB_BULK in > 1716 16.699915 1.6.1 host USBMS 40 SCSI: Response LUN: 0x00 (Test Unit > Ready) (Good) > 1717 17.709334 host 1.6.1 USBMS 58 SCSI: Test Unit Ready LUN: 0x00 > 1718 17.709547 1.6.1 host USB 27 URB_BULK out > 1719 17.709552 host 1.6.1 USB 27 URB_BULK in > 1720 17.709586 1.6.1 host USBMS 40 SCSI: Response LUN: 0x00 (Test Unit > Ready) (Good) > 1721 18.712864 host 1.6.1 USBMS 58 SCSI: Test Unit Ready LUN: 0x00 > 1722 18.713081 1.6.1 host USB 27 URB_BULK out > 1723 18.713086 host 1.6.1 USB 27 URB_BULK in > 1724 18.713148 1.6.1 host USBMS 40 SCSI: Response LUN: 0x00 (Test Unit > Ready) (Good) > 1741 19.735245 host 1.6.1 USBMS 58 SCSI: Test Unit Ready LUN: 0x00 > 1742 19.735410 1.6.1 host USB 27 URB_BULK out > 1743 19.735415 host 1.6.1 USB 27 URB_BULK in > 1744 19.735474 1.6.1 host USBMS 40 SCSI: Response LUN: 0x00 (Test Unit > Ready) (Good) > 1811 20.747477 host 1.6.1 USBMS 58 SCSI: Test Unit Ready LUN: 0x00 > 1812 20.747699 1.6.1 host USB 27 URB_BULK out > 1813 20.747704 host 1.6.1 USB 27 URB_BULK in > 1814 20.747766 1.6.1 host USBMS 40 SCSI: Response LUN: 0x00 (Test Unit > Ready) (Good) > 1905 21.755419 host 1.6.1 USBMS 58 SCSI: Test Unit Ready LUN: 0x00 > 1906 21.755579 1.6.1 host USB 27 URB_BULK out > 1907 21.755584 host 1.6.1 USB 27 URB_BULK in > 1908 21.755674 1.6.1 host USBMS 40 SCSI: Response LUN: 0x00 (Test Unit > Ready) (Good) > 1911 22.769205 host 1.6.1 USBMS 58 SCSI: Test Unit Ready LUN: 0x00 > 1912 22.769355 1.6.1 host USB 27 URB_BULK out > 1913 22.769360 host 1.6.1 USB 27 URB_BULK in > 1914 22.769415 1.6.1 host USBMS 40 SCSI: Response LUN: 0x00 (Test Unit > Ready) (Good) Unless the Kindle advertises removable media, there doesn't seem to be any real point to all those TEST UNIT READY commands. Unless they are what prevents the disconnections... > How can I get further on this topic? Is runtime power management enabled? Maybe the Kindle disconnects whenever the computer tries to suspend it. This typically happens 2 seconds after the last command was issued, which matches your observations. If runtime PM is enabled, you can try disabling it. Alternatively, a number of Linux kernel developers work for Amazon (or at least, use email addresses ending in "@amazon.com"), as shown by the MAINTAINERS file. Maybe one of them can get in touch with the Kindle software development people and find the actual answer. Alan Stern
