[U-Boot] [PATCH v2 2/2] cmd: Add 'bcb' command to read/modify/write BCB fields

[Sam Protsenko]

Anyway, from my side:

Reviewed-by: Sam Protsenko <semen.protsenko at linaro.org>

On Mon, May 20, 2019 at 6:16 PM Sam Protsenko
<semen.protsenko at linaro.org> wrote:
>
> Hi Eugeniu,
>
>
> On Mon, May 20, 2019 at 10:23 AM Eugeniu Rosca <erosca at de.adit-jv.com> wrote:
> >
> > Hi Simon
> > cc: Sam, Igor, feel free to correct/augment anything of below
> >
> > On Sat, May 18, 2019 at 10:33:02AM -0600, Simon Glass wrote:
> > > Hi Eugeniu,
> > >
> > > On Fri, 17 May 2019 at 08:46, Eugeniu Rosca <erosca at de.adit-jv.com> wrote:
> > > >
> > > > 'Bootloader Control Block' (BCB) is a well established term/acronym in
> > > > the Android namespace which refers to a location in a dedicated raw
> > > > (i.e. FS-unaware) flash (e.g. eMMC) partition, usually called "misc",
> > > > which is used as media for exchanging messages between Android userspace
> > > > (particularly recovery [1]) and an Android-capable bootloader.
> > > >
> > [..]
> > >
> > > Where is this documented? Perhaps it should go in README.avb2?
> >
> > README.avb2 is solely about the "verified/secure" booting of Android,
> > while the 'bcb' command proposed in this patch can be useful both in
> > verified boot scenarios (e.g. full-featured U-Boot builds), as well
> > as in non-avb ones (e.g. development, PoC, demos, custom
> > configurations). Thus, I think that README.avb2 is not the best
> > place for 'bcb'.
> >
> > More generally, as somebody who uses git as an extension of himself, I
> > am quite happy with commit-only documentation. OTOH, for those who
> > receive U-Boot in tarballs or expect source-level docs/tutorials, I
> > agree that having the 'bcb' described in a README might be helpful.
> >
> > I can identify two Android-dedicated README files, but none of them
> > seems to be suitable for the new command:
> >  - doc/README.android-fastboot
> >  - doc/README.avb2
> >
> > Igor, Sam, what's your view on the above? Would you suggest creating
> > a doc/README.android-bcb or there is a more elegant solution to it?
> >
>
> Documentation would be nice. Although you already provided a generic
> description of 'bcb' command in 'help bcb', the user often wants to
> read more high-level documentation. I'd say, you can copy the
> description from commit message to doc/README.android-bcb, extending
> it with usual use-cases, and how this command can be used in those
> use-cases. For example, your pseudo-code for reboot reason you
> provided to me earlier, etc. Also, it can be useful to mention if
> Google have any requirements (mandatory or optional) for the
> bootloader (misc partition, reboot reason, recovery, etc), and how
> this 'bcb' command can help in those requirements implementation.
>
> All that said, IMHO documentation/test wise: it's not critical in this
> case, you can add that later, just to speed-up the whole development
> process and divide it into iterations. But that's for maintainers to
> decide, of course.
>
> Also, I've a feeling that we have another problem, more common than
> just a documentation. At the moment we have a bunch of Android related
> features, which don't have namespace separation on several levels:
>  - file/directories: we may want to move all Android related commands
> to sub-directory
>  - commands: we may want to add main command called "android" for all
> Android-related commands, or maybe just a prefix
>  - Kconfig: we may want to have some generic naming scheme for all
> Android-related commands
>  - Documentation, tests: the same here
>
> So at some point we will probably need to discuss and fix that
> somehow. Not here, of course :)
>
> > >
> > > Should it default to enabled if avb is used?
> >
> > I think at this specific moment in time, 'bcb' is orthogonal (meaning it
> > is neither a direct, nor a reverse dependency) to any other Android
> > feature in U-Boot. This could be re-assessed, if platform maintainers
> > start to rely on 'bcb' in their U-Boot environments on regular basis.
> >
> > --
> > Best Regards,
> > Eugeniu.