[U-Boot] Issue with USB mass storage (thumb drives)

[Simon Glass <sjg@chromium.org>]

Hi,

On 24 February 2016 at 10:43, Marek Vasut <marex@denx.de> wrote:
>
> On 02/23/2016 07:38 AM, Hannes Schmelzer wrote:
> > On 22.02.2016 18:59, Fabio Estevam wrote:
> >> On Mon, Feb 22, 2016 at 2:51 PM, Maxime Jayat <jayatmaxime@gmail.com>
> >> wrote:
> >>
> >>> Hello,
> >>> I was hit by the same problem, where my USB SD card reader would timeout
> >>> in U-boot when reading a large file (16 MB). Changing USB_MAX_XFER_BLK
> >>> to 32767 fixed the problem but I investigated a little more.
> >>> I was curious to see what the Linux kernel used, because it had no
> >>> problem reading the file. In Linux, USB_MAX_XFER_BLK corresponds to
> >>> max_sector in the scsiglue, which is set to 240 blocks per transfer by
> >>> default, and is tunable via sysfs.
> >>> There is also a list of unusual devices which needs no higher than 64
> >>> blocks per transfer.
> >>> The linux USB FAQ has a very interesting entry about this which explains
> >>> the rationale for this value:
> >>>      http://www.linux-usb.org/FAQ.html#i5
> >>>
> >>> FWIW: my USB card reader is
> >>> 0bda:0119 Realtek Semiconductor Corp. Storage Device (SD card reader)
> >>>
> >>> I've benchmarked in U-boot the time impact of this change.
> >>> For reading my 16764395 bytes file:
> >>> USB_MAX_XFER_BLK        Read duration (as reported by U-boot):
> >>> 64                      3578 ms
> >>> 128                     2221 ms
> >>> 240                     1673 ms
> >>> 32767                   1020 ms
> >>> 65535                   974  ms
> >>>
> >>> So there is definitely a strong impact for lower values.
> >> Ok, so with a USB_MAX_XFER_BLK size of 32767 there is not so much of a
> >> performance impact.
> >>
> >> Looks like that changing USB_MAX_XFER_BLK from 65535 to 32767 is the
> >> way to go.
> > I have configured a value of 8191 some few weeks ago on my zynq board,
> > there was no negative feedback until yesterday :-(
> >
> > A colleague of mine told me, that his USB-stick doesn't work. I had a look.
> >
> > Vendor: 0x1307  Product 0x0165 Version 1.0
> > I had to reduce the USB_MAX_XFER_BLK downto 2048 to make it work.
> >
> > I'm not the big usb-expert ... but would it be possible to move away
> > from this
> > #define to some variable which is adapted to the lowest value on the bus.
> > Is it possible at all to get to right value out of some register ?
>
> We will probably need a quirk table and for the crappy USB sticks, we
> will just have to use lower maximum xfer size. I would suggest to add
> an environment variable, which would allow to override the max xfer
> size. This would help in case the user had a device, which does need
> a quirk, but is not yet in a quirk table ; as a temporary work around of
> course.

Yes.

Even better if we can print a message telling the user about this when
we detect this error.

Regards.
Simon