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

[Hannes Schmelzer]

On 22.02.2016 18:59, Fabio Estevam wrote:
> 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.
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 ?

regards,
Hannes