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

[Marek Vasut <marex@denx.de>]

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.