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SubjectRe: USB serial regression ->

> The device presented two LUNs on the mass-storage interface. LUN 0 was
> the emulated CDROM (named "Mass Storage") and LUN 1 was direct-access
> (named "SD Storage"). LUN 0 appeared to work normally, although it
> reported Not Ready, No Medium Present errors. LUN 1 did the same
> thing, but in its response to the REQUEST SENSE command it set the
> additional-sense-length byte to 0x12 instead of 0x0a, for no apparent
> reason. This caused usb-storage to assume the device supported SANE
> SENSE, which presumably it doesn't.

Interesting. Under the windows, the device exposes a CD-ROM (which
contains windows SW for it). It also has an micro-SD connector as some
kind of "bonus" though I've never used it.

> Further REQUEST SENSE commands therefore requested 96 bytes of data
> instead of the standard 18 bytes. With LUN 0 this worked okay. But
> with LUN 1 it didn't; the device reported a failure of the REQUEST
> SENSE. This is what caused usb-storage to issue the device reset.

Might be interesting to see what happens with a micro-SD actually in the
slot. Also, doing a device-reset on a multi-function device because one
of the functions isn't too happy may be a tad harsh no ?

> After the reset usb-storage continued to ask for 96 bytes of sense
> data, and LUN 1 continued to fail the commands. Hence the repeated
> resets.


> Thus the two bugs in the Huawei device are: Incorrect
> additional-sense-length byte for LUN 1, and incorrect CSW for a 96-byte
> I can see two approaches for working around this. The first is to make
> the SENSE SENSE test more discriminating. For example, test for
> additional-sense-length values larger than 0x12 instead of larger than
> 0x0a. Ben Efros, would this be acceptable?
> The second approach is to add a SINGLE_LUN flag to all the Huawei
> entries in unusual_devs.h. It's not clear that this is a good idea; if
> one of those devices really does have an SD card then people might want
> to be able to use it.

They do have an SD slot indeed.

Any pointer to the piece of code I can tweak to change 0xa to 0x12
(SENSE stuff) to see if that helps ?


> Alan Stern
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