I have a (cheap and nasty) EM732X MP3 player made by Yifang Digital:
http://www.yifangdigital.com/Portals/118056c2de4d/40f5a5ace647/c7d06f0150.html
which doesn't work out of the box on Linux: there are I/O errors on
read and write. This turns out to be because it can't handle attempts
to transfer 32KB or more in one go: if /sys/block/sda/device/max_sectors
is set to 63 then it works; if set to 64 it does not:
usb-storage: usb_stor_bulk_transfer_sglist: xfer 32768 bytes, 8 entries
usb-storage: Status code 0; transferred 32768/32768
usb-storage: -- transfer complete
usb-storage: Bulk data transfer result 0x0
usb-storage: Attempting to get CSW...
usb-storage: usb_stor_bulk_transfer_buf: xfer 13 bytes
usb-storage: Status code 0; transferred 13/13
usb-storage: -- transfer complete
usb-storage: Bulk status result = 0
usb-storage: Bulk Status S 0x53425355 T 0x8c R 4294901760 Stat 0x0
usb-storage: -- unexpectedly short transfer
usb-storage: scsi cmd done, result=0x10070000
Note that the Residue here is 0xFFFF0000 -- looks suspiciously to
me like something overflowing a signed 16 bit int in the device...
Anyway, there's already special casing for some other device with
a similar problem in slave_configure() in drivers/usb/storage/scsiglue.c,
and I was just going to write a patch to add this device, but:
(1) shouldn't this be rolled into the unusual_devs.h list rather than
being hardcoded inside scsiglue.c?
(2) the existing special case just checks the Vendor ID, but my device
has a vendor ID of 0419, which the webpage says is Samsung --
applying the workaround to all Samsung devices seems a bit broad
and I wasn't sure how best to narrow it down.
Here's the stanza from /proc/bus/usb/devices:
T: Bus=04 Lev=01 Prnt=01 Port=01 Cnt=01 Dev#= 3 Spd=12 MxCh= 0
D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=16 #Cfgs= 1
P: Vendor=0419 ProdID=aaf8 Rev= 1.00
C:* #Ifs= 1 Cfg#= 1 Atr=c0 MxPwr=100mA
I: If#= 0 Alt= 0 #EPs= 3 Cls=08(stor.) Sub=06 Prot=50 Driver=usb-storage
E: Ad=82(I) Atr=02(Bulk) MxPS= 64 Ivl=0ms
E: Ad=03(O) Atr=02(Bulk) MxPS= 64 Ivl=0ms
E: Ad=81(I) Atr=03(Int.) MxPS= 8 Ivl=255ms
I'm using kernel 2.6.14.3, but kernel.org suggests that scsiglue.c
is still the same in Linus' latest kernel.
[NB: I'm not subscribed to this mailing list but will be reading replies
via the web archive; however, if you could CC me on replies I'd be
grateful.]
thanks in advance
-- PMM
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