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.