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.