[PATCH V2] dt-bindings: nvmem: u-boot, env: add Broadcom's variant binding

[Rob Herring]

On Tue, Oct 18, 2022 at 9:10 AM Conor Dooley <conor.dooley at microchip.com> wrote:
>
> On Tue, Oct 18, 2022 at 03:58:38PM +0200, Rafał Miłecki wrote:
> > On 18.10.2022 12:19, Conor Dooley wrote:
> > > On Fri, Oct 14, 2022 at 04:09:40PM -0500, Rob Herring wrote:
> > > > On Fri, 30 Sep 2022 18:36:31 +0200, Rafał Miłecki wrote:
> > > > > From: Rafał Miłecki <rafal at milecki.pl>
> > > > >
> > > > > Broadcom uses U-Boot for a lot of their bcmbca familiy chipsets. U-Boot
> > > > > stores its configuration in an environment data block.
> > > > >
> > > > > Such blocks are usually stored on flash as a separated partition at
> > > > > hardcoded address. Broadcom however decided to:
> > > > > 1. Store env data block inside U-Boot partition
> > > > > 2. Avoid sticking to hardcoded offsets
> > > > > 3. Use custom header with "uEnv" magic and env data length
> > > > >
> > > > > Example (length 0x4000):
> > > > > $ hexdump -n 32 -C -s 0x40000 /dev/mtdblock0
> > > > > 00040000  76 6e 45 75 00 40 00 00  34 89 7a 82 49 4d 41 47  |vnEu. at ..4.z.IMAG|
> > > > > 00040010  45 3d 4e 41 4e 44 3a 31  4d 2c 31 30 32 34 4d 00  |E=NAND:1M,1024M.|
> > > > > (0x40000 offset is unit specific and can change)
> > > > >
> > > > > Starting with the commit 118f3fbe517f4 ("dt-bindings: mtd: partitions:
> > > > > support label/name only partition") DT can describe partitions matching
> > > > > them by a name (without specifying actual address). With that feature
> > > > > and this binding change it's possible to:
> > > > > 1. Specify DT node for Broadcom's U-Boot env data subpartition
> > > > > 2. Add nodes for specific environment data variables
> > > > > 3. Reference them as NVMEM cells
> > > > >
> > > > > This binding is unlikely to help Broadcom's U-Boot. U-Boot SPL needs to
> > > > > find environment data early (before it accesses DTB) and it does that by
> > > > > looking for an "uEnv" magic. Dirty way.
> > > > >
> > > > > This binding can however be used by operating systems. It allows
> > > > > describing cleanly U-Boot, its env data and variables. It tells
> > > > > operating system about Broadcom-specific env data so it can parse it.
> > > > >
> > > > > Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
> > > > > ---
> > > > > V2: Work on better commit body & add example
> > > > > ---
> > > > >   .../devicetree/bindings/nvmem/u-boot,env.yaml | 21 +++++++++++++++++++
> > > > >   1 file changed, 21 insertions(+)
> > > > >
> > > >
> > > > Applied, thanks!
> > >
> > > Hey Rob,
> > > Maybe my tooling is out of date or w/e but this is breaking
> > > dt_binding_check for me.
> > >
> > > I applied the below to fix the build, which I was about to send, before
> > > realising that you'd applied it and wondered if I was missing something.
> >
> > Thanks for catching that and submitting a fix!
>
> No worries.
>
> >
> > I guess I didn't run dt_binding_check this time or I did it before
> > adding an example. Sorry for that!
>
> BTW, subsequent to sending the fix I double checked my dt_binding_check
> logs and I saw:
> Documentation/devicetree/bindings/nvmem/u-boot,env.example.dtb: partition at 0: Unevaluated properties are not allowed ('partition-u-boot-env' was unexpected)
>         From schema: Documentation/devicetree/bindings/mtd/partitions/u-boot.yaml
>
> I think unevaluated property detection got better in v2022.08 of
> dt-schema so that is probably worth fixing too. I'll leave that one up
> to you ;)

Sigh. The simple fix is add 'partition-u-boot-env' to u-boot.yaml. But
now I have no idea if that is really complete as this Broadcom stuff
is coming in bit by bit. So I've now just dropped everything. Please
resend with it all fixed.

Rob