Re: [PATCH v1 2/4] arm64: dts: qcom: sc7280: Add 'piglin' to the crd-r3 compatible strings

[Rajendra Nayak]

On 3/21/2022 11:30 PM, Doug Anderson wrote:
> "Hi,
>
> On Mon, Mar 21, 2022 at 8:14 AM Matthias Kaehlcke <mka@xxxxxxxxxxxx> wrote:
> > On Mon, Mar 21, 2022 at 11:14:56AM +0530, Rajendra Nayak wrote:
> > > On 3/17/2022 5:58 AM, Matthias Kaehlcke wrote:
> > > > With newer bootloader versions the crd-r3 (aka CRD 1.0 and 2.0) is
> > > > identified as a 'piglin' board (like the IDP2 board), instead of 'hoglin'
> > > > Add the compatible strings 'google,piglin-rev{3,4}'. The hoglin entries
> > > > are kept to make sure the board keeps booting with older bootloader
> > > > versions.
> > >
> > > The older bootloaders really look for the google,hoglin-rev3/google,hoglin-rev4
> > > compatibles or just google,hoglin? If its just google,hoglin, won;t it pick the
> > > crd-rev5+ dtb now?
> >
> > They look for the -revN compatible, I confirmed that on my CRD 2.0.
>
> Thanks for confirming Matthias! I'll also note that, in general, these
> "google,board-revX" type compatible strings are all programmatically
> generated. You can see at:
>
> https://chromium.googlesource.com/chromiumos/platform/depthcharge/+/refs/heads/main/src/boot/fit.c#70
>
> ...and whenever it's using this normal logic then it has a standard
> fallback mechanism in place. On a random board in front of me
> depthcharge prints out:
>
> Compat preference: google,lazor-rev3-sku0 google,lazor-rev3
> google,lazor-sku0 google,lazor
>
> So it'll first try the very specific verison with rev and sku. Then
> just by rev. Then just by sku. ...and if none of those match it'll
> pick a device tree that has neither. The "newest" device tree always
> has no revision number specified and that way if software doesn't
> change but the revision bumps then we have no problem. We only add the
> revision info for old boards.

Thanks Matthias/Doug for the clarification,

Reviewed-by: Rajendra Nayak <quic_rjendra@xxxxxxxxxxx>

> There are a few cases where we add special compatible strings and
> these don't match on board/rev. This is fairly uncommon, though. You
> might be aware of the special case of adding "qcom,sc7180-idp"
> (without rev/sku matching) for "bubs". See:
>
> https://chromium.googlesource.com/chromiumos/platform/depthcharge/+/refs/heads/main/src/board/trogdor/board.c#136
>
>
> -Doug