[U-Boot] [PATCH v3 4/5] usb/gadget: add the fastboot gadget

[Lukasz Majewski]

Hi Marek,

> On Friday, April 11, 2014 at 02:55:31 PM, Rob Herring wrote:
> > On Fri, Apr 11, 2014 at 2:14 AM, Bo Shen <voice.shen at atmel.com>
> > wrote:
> > > Hi Rob Herring,
> > > 
> > >   I am just do a function testing on Atmel sama5d3xek board. And
> > > a small
> > > 
> > > comment as following.
> > > 
> > >   Btw, do you test to transfer big size file. I try a file bigger
> > > than
> > > 
> > > 100MiB, it will hang. However use DFU or RNDIS don't meet this
> > > issue.
> > 
> > How much RAM do you have? It will happily download into the end of
> > RAM overwriting u-boot if loadsize is not set. DFU at least has its
> > own buffer size configuration.
> 
> I really have to wonder ... why does android not use DFU

Unfortunately the DFU has its own limitations. The most notable one is
using only EP0 for transmission. As a result the transmission speed is
slow when compared with other solutions, which are using other EPs.

> instead and
> instead forces us to take in yet another (fourth ? ... CDC ethernet,
> DFU, Thor, Fastboot)

A little explanation:
1. UMS (CDC Ethernet) - export the content of the whole flash. It should
be regarded as a convenient debug option. It is somewhat clumsy
to use dd if=/u-boot.bin of=/dev/sda1 .... to store u-boot.

2. DFU it is the standard - devised at 2004 - rather outdated now. It is
slow but reliable - targeted to uC flashing.

3. Thor, fastboot - protocols devised to provide faster transmission
rates (they use other EPs for transmission).

> usb image download protocol someone invented
> without cooperating with the rest of the community on a common and
> functional solution? Sigh :'-(

I think, that this problem emerged because of the lack of DFU standard
update - adding better checksumming and possibility for using other EPs
would solve the problem.

In u-boot it is not a big problem, since we are using one backend
(dfu_write()) to store data on the medium. Moreover common gadget code
- g_dnl.c is available to reduce code duplication.

To add support for other gadget one needs to implement proper function
(like f_thor.c, f_dfu.c, f_fastboot.c).

> 
> Best regards,
> Marek Vasut



-- 
Best regards,

Lukasz Majewski

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