On Tue, Mar 16, 2021 at 06:26:30AM +0100, Matthias Schwarzott wrote:

I implemented solution 3b. This is the pullrequest for udev (systemd
repository):

	https://github.com/systemd/systemd/pull/19002

Now Lennart asks if udev is the best place for such hacks/work-arounds?

Well, I implemented it as suggested by Alan (see above). This was the
simplest of the considered alternatives. Different quirks in kernel has been
considered, but are more effort to be implemented.

Lennart probably isn't aware how the usb-storage driver works.  It does 
not create commands on its own; it merely sends the commands that it 
gets from higher SCSI layers.

It may be possible to modify the SCSI core, to make it send a TEST UNIT 
READY command immediately following any SYNCHRONIZE CACHE to a Kindle.

However, there may be an easier solution.  usb-storage does indeed send 
a command of its own, REQUEST SENSE, to get error data when a command 
fails.  The patch below will make it do the same thing whenever it sends 
a SYNCHRONIZE CACHE to a Kindle, failure or not.

The only question is whether the Kindle will regard REQUEST SENSE as a 
sufficient indication that it shouldn't do an eject.  The only way to 
find out is by testing the patch.

Alan Stern



Index: usb-devel/drivers/usb/storage/transport.c
===================================================================

--- usb-devel.orig/drivers/usb/storage/transport.c
+++ usb-devel/drivers/usb/storage/transport.c

@@ -656,6 +656,13 @@ void usb_stor_invoke_transport(struct sc
 		need_auto_sense = 1;
 	}
 
+	/* Some devices (Kindle) require another command after SYNC CACHE */
+	if (us->fflags & US_FL_CHECK_AFTER_SYNC &&
+			srb->cmnd[0] == SYNCHRONIZE_CACHE) {
+		usb_stor_dbg(us, "-- sense after SYNC CACHE\n");
+		need_auto_sense = 1;
+	}
+
 	/*
 	 * If we have a failure, we're going to do a REQUEST_SENSE 
 	 * automatically.  Note that we differentiate between a command

Index: usb-devel/drivers/usb/storage/unusual_devs.h
===================================================================

--- usb-devel.orig/drivers/usb/storage/unusual_devs.h
+++ usb-devel/drivers/usb/storage/unusual_devs.h

@@ -2212,6 +2212,18 @@ UNUSUAL_DEV( 0x1908, 0x3335, 0x0200, 0x0
 		US_FL_NO_READ_DISC_INFO ),
 
 /*
+ * Reported by Matthias Schwarzott <zzam@gentoo.org>
+ * The Amazon Kindle treats SYNCHRONIZE CACHE as an indication that
+ * the host may be finished with it, and automatically ejects its
+ * media unless it receives another command within one second.
+ */
+UNUSUAL_DEV( 0x1949, 0x0004, 0x0000, 0x9999,
+		"Amazon",
+		"Kindle",
+		USB_SC_DEVICE, USB_PR_DEVICE, NULL,
+		US_FL_CHECK_AFTER_SYNC ),
+
+/*
  * Reported by Oliver Neukum <oneukum@suse.com>
  * This device morphes spontaneously into another device if the access
  * pattern of Windows isn't followed. Thus writable media would be dirty

Index: usb-devel/include/linux/usb_usual.h
===================================================================

--- usb-devel.orig/include/linux/usb_usual.h
+++ usb-devel/include/linux/usb_usual.h

@@ -86,6 +86,8 @@
 		/* lies about caching, so always sync */	\
 	US_FLAG(NO_SAME, 0x40000000)				\
 		/* Cannot handle WRITE_SAME */			\
+	US_FLAG(CHECK_AFTER_SYNC, 0x80000000)			\
+		/* Check sense after SYNCHRONIZE_CACHE */	\
 
 #define US_FLAG(name, value)	US_FL_##name = value ,
 enum { US_DO_ALL_FLAGS };