Linux scsi / usb-mass-storage and HP printer cardreader bug + fix

[Hans de Goede]

Hi All,

First of all sorry for the somewhat massive cross-posting, I've spend a 
significant amount of time hunting down this bug, and so far the response has 
been less the overwhelming.

The problem is with the HP PSC 1350 (my printer and confirmed by 2 others) and 
atleast also the HP PSC 1610 (confirmed by Guillaume Bedot, in the CC).

The cardreader of the multi function printers will "crash" and from that moment 
on no longer communicate in any sane way, if you try to read the last sector of 
an sdcard* in a read that is more then 1 sector, so trying to read 8 sectors 
starting at sector capicity-8 will crash it, as will reading 2 sectors starting 
at sector capicity-2, however reading the last sector in a one 1 sector read 
will succeed! (* xdcards seem to be fine).

I haven't tried if it will crash on larger then 1 sector writes which include 
the last sector too, I immediately added code to not do that in both the read 
and write paths. I have tested reading and writing the end of the disk with 
this kludge in and it works.

I currently have a somewhat ugly proof of concept patch for this, which adds 
another type of usb-massstorage quirk. When this quirk flag is set, the 
usb-massstorage driver modifies READ_10 and WRITE_10 commands of more then 1 
sector which includes the last sector to become one sector less. I've been told 
by scsi subsystem developers that doing a shorter read / write then requested 
is not a problem, the scsi subsystem is designed to handle getting less then it 
asked for and will send a seperate request for the last sector.

I and 3 others (2 on a PSC 1350 too, one on a PSC1610) have tested this patch 
with success. I'm not asking for this patch to be included to the kernel as is, 
I'm asking for the now known workaround for this to be added to the kernel in 
someway!

Perhaps its an idea to add the posibility to have a scsi command filter 
function / callback to the scsi or usb-massstorage subsystem, and then add a 
mechanism to set this filter depending on usb id's and if added to the scsi 
layer, a mechanism to set it based on scsi device and manufacturer 
identification strings. Such a mechanism might be usefull in the future to work 
around other broken hardware too, and has the added advantage of not having 
todo much changes to the normal code path, keep that readable.

I'm willing to come up with a patch for such a filter mechanism, provided I get 
some pointers where this is best added.

Thanks & Regards,

Hans


p.s.

I've also included the fedora-kernel list in the addressee's because I was 
hoping that maybe someone can take one of these printers to the kernel hackfest 
   in the weekend's fudcon and take a look at this.
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