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

[Fabio Estevam]

On Mon, Feb 22, 2016 at 2:51 PM, Maxime Jayat <jayatmaxime at 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.