[U-Boot] strawman Fastboot in U-Boot Design Doc

[Wolfgang Denk]

Dear John Rigby,

In message <BANLkTinFHTff5Scr_uP6KNBXQKP3SvVB5A at mail.gmail.com> you wrote:
> Here a first draft design doc.  It is based in part on the Fastboot
> implementation in the rowboat git repo (pointer below).

Thanks.

> Hooks into U-Boot
> =================
> 
> Fastboot gets access to the USB subsystem via the same interfaces as USB_TTY,
> namely the udc_* api's:

Does it make sense to restrict this to USB?  Or should we decouple the
protocol part from the actual transport path?  Maybe it would make
sense to provide the same feature over plain serial line, or over
Ethernet?

Also please keep in mind that there are many ways how a system can
interact with the "operator": we have plain old serial console,
netconsole, console over serial over USB, netconsole over Ethernet
over USB, ...

We should make sure that at least on the conceptual level adding
fastboot support will not cause any conflicts.

> Startup
> =======
> 
> Fastboot will be started on the target by issuing the "fastboot" command.

OK.

> Optionally a board specific startup method may exist.  For example if
> a certain combination of keys is pressed on reset then fastboot will be
> started immediately.

This has nothing to do with fastboot, and should be kept as a separate
item.  Normally U-Boot allows, when keys are supported, to map any
combination of key presses to any commands, i. e. this is in no way
restricted to or dependent on fastboot support.

> Shutdown
> ========
> 
> Once started the fastboot command will continue until:
> 	<CTRL-C> is typed on the console
> 	a "continue" command is sent from the host
> 	usb cable is removed
> 	no commands have been sent from the host for some configurable timeout

This probably needs configuration.

"usb cable is removed" probably makes little sense when running
fastboot protocol over a serial port.

Also, this feature would require permanent polling of the USB status.
Is this needed?

> Coexistance With USB_TTY and DFU
> ================================
> 
> One should be able to enable USB_TTY, DFU and Fastboot at compile time
> and chose one at runtime.

I'm not sure what exactly you mean by "chose one at runtime". It is
pretty much clear that you don't want to run DFU and fastboot
simultaneously, but it is very likely that we will need USB_TTY (for
console over USB) or even Ethernet over USB for console and then want
to start fastboot.

I think I remember that fastboot may require "adjustments" of the USB
IDs and such - we will have to make sure that things like that do not
cause conflicts.

An area that raises additional questions is error handling. When
running fastboot over USB and with a serial console it is probably a
very good idea to provide error messages and maybe even status
reports on the console.  Will this still work with USB_TTY or
netconsole over Ethernet over USB?

> Questions
> ========
> 
> Should a Fastboot host program be included in the U-Boot source?

Seems some peole want it...

> Could Fastboot be implemented as an extension to USB_TTY?

I think we should at least split protocol handling and communication
layer.

> Could Fastboot, DFU and USB_TTY share a layer of code above the
> udc_* api's?

At least they will have to co-exist with each other.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
"A dirty mind is a joy forever."                       - Randy Kunkee