[U-Boot] [PATCH] usb:composite:fix Provide function data when addressing device with only one interface

[Lukasz Majewski]

On Thu, 27 Jun 2013 21:36:09 +0000 (UTC), Tormod Volden wrote:

Hi Tormod,

> Lukasz Majewski writes:
> > 
> > This commit fixes problems with some non-standard requests send with
> > device address instead of interface address
> > (bmRequestType.Receipent field).
> > 
> > This happens with dfu-util (debian version: 0.5), which address non
> > standard requests (like w_value=0x21 and bRequest=GET_DESCRIPTOR)
> > to device.
> 
> 
> Dear u-boot developers,
> 
> The above comment seems to imply that dfu-util is sending non-standard
> requests. For the record, that would be wrong. dfu-util is sending a
> standard "get descriptor" request. These always go to the device, not
> to an interface. The descriptor it is asking for is, although not
> mandatory per the core USB standard, a class-specific descriptor
> which is part of the DFU 1.0 standard. So this is all standard.
> 
> While on this topic, I would recommend that you include this
> descriptor in the configuration descriptor set, that is, in the
> complete configuration descriptor that the host OS usually requests
> during enumeration. Also this class-specific descriptor belongs here.
> In that case, the OS and libusb will keep a copy of this descriptor,
> and dfu-util will not have to send an explicit request (through
> libusb_get_descriptor()) to retrieve it.

Thanks for explanation. The commit about which we are discussing was a
(reasonable) fix for the problem.  

I need to look into this and came up with proper solution.

> 
> 
> > Without this fix, the above request is STALLED, and hence causes
> > dfu-util to assume some standard configuration (packet size = 1024B
> > instead of 4096B)
> 
> Note that this number is the "Maximum number of bytes that the device
> can accept per control-write transaction."

I need to check this, but AFAIR there was a problem with dfu-util (and
probably libusb under the hood) version 0.1 (shipped with "ancient"
old stable debian) and 0.5 which is currently in use.

> 
> The DFU transactions should work fine if a smaller packet size is
> used - as long as it is larger or equal to the bMaxPacketSize0. Of
> course, smaller packets will cause more overhead and be less
> efficient, but you must make sure that your device can handle this. I
> am not sure from these comments whether the smaller packet size
> caused errors in your implementation, or if the problem was just
> reduced performance.

The change was driven by the need to improve performance, when
downloading large files (with roofts) and to silent warning on the
dfu-util side.

> 
> Best regards,
> Tormod Volden
> 
> 
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-- 
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group