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 <z...@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 <oneu...@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 };
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