Hi,
Some mass storage devices return a bogus value in response to a Get Max LUN request. The Iomega Jaz USB Adapter responds with 0x10, hence my recent patch to use the US_FL_SINGLE_LUN quirk for it.
The USB MSC Bulk Only Transport document says "The device shall return one byte of data that contains the maximum LUN supported by the device."
Since the LUN field in the command block wrapper is only 4 bits wide, it might be helpful to report too-large LUN values in the kernel log, and assume max LUN is actually 0. That could get some devices which currently need the US_FL_SINGLE_LUN quirk to work.
Patch below, though whether it's worth applying might depend on whether any other devices have the same problem.
Signed-off-by: Mark Knibbs <markk@xxxxxxxxxxx>
---
diff -upN linux-3.17/drivers/usb/storage/transport.c.orig linux-3.17/drivers/usb/storage/transport.c
--- linux-3.17/drivers/usb/storage/transport.c.orig 2014-10-05 20:12:36.000000000 +0100
+++ linux-3.17/drivers/usb/storage/transport.c 2014-10-12 13:11:38.000000000 +0100
@@ -1035,9 +1035,20 @@ int usb_stor_Bulk_max_lun(struct us_data
usb_stor_dbg(us, "GetMaxLUN command result is %d, data is %d\n",
result, us->iobuf[0]);
- /* if we have a successful request, return the result */
- if (result > 0)
- return us->iobuf[0];
+ /*
+ * If we have a successful request, return the result if valid. The
+ * CBW LUN field is 4 bits wide, so the value reported by the device
+ * should fit into that.
+ */
+ if (result > 0) {
+ if (!(us->iobuf[0] & 0xf0)) {
+ return us->iobuf[0];
+ } else {
+ dev_info(&us->pusb_intf->dev,
+ "Max LUN %d is not valid, using 0 instead",
+ us->iobuf[0]);
+ }
+ }
/*
* Some devices don't like GetMaxLUN. They may STALL the control
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