Re: [RFC V2 PATCH 10/12] arm64: dts: msm8994 issolate non standard bootloader/LK entries

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Fri 21 Oct 13:04 PDT 2016, Stephen Boyd wrote:

> On 10/21, Bjorn Andersson wrote:
> > On Wed 19 Oct 20:17 PDT 2016, Andy Gross wrote:
> > 
> > > On Wed, Oct 19, 2016 at 08:07:25PM -0500, Rob Herring wrote:
> > [..]
> > > > Makes sense to me for things like Nexus phones here. What about DB410
> > > > for example? Is there hope for a fix there? My bootloader is only a
> > > > couple of months old and needs the properties still.
> > > 
> > > There won't be a fix for the 410c.  We barely got them to respin to use PSCI.
> > > Stephen can correct me if I am wrong on this.
> > > 
> > > If this is fixed, it would be 8996+.  If..........
> > > 
> > > So this means introducing the msm-id's for the boards that currently require it,
> > > and for the boards that will require it in the future.  And this would stay in
> > > effect until the bootloader is able to parse the compatible strings or figure
> > > this out without the msm-ids.
> > > 
> > 
> > But if the bootloader at any point in the future would support picking a
> > dtb by compatible strings instead of {msm,board,pmic}-id we wouldn't we
> > just be back to the ridiculous compatible strings that tipped over into
> > acceptance to these ids in the first place.
> > 
> > Or do we expect the boot loader to do a deep scan of the dtb to match on
> > multiple nodes from the tree?
> 
> I'm pushing the bootloader team to do the deep scan of the dtb to
> match up board compatible and pmic compatible strings so that we
> don't have to keep these numbers around. Basically put what
> dtbtool is doing into the bootloader so we don't have to post
> process the dtb anymore. We're currently discussing how to
> implement it and how to move the internal codebase to the new
> scheme.
> 

Based on the variations described in your "Document qcom board
compatible format" patch you would need to scan the DTB for:

* SoC, Platform type and Version
  All part of /compatible, so that's simple

* Memory size
  Look at second cell of /memory/reg ? Or just reject this variable?

* PMIC
  Find the qcom,spmi-pmic-arb and iterate over each child and match the
  compatible of with some predefined list. We need to add all version
  variations of these in the compatibles to make this work as well.

* Main storage technology
  Look for an active node compatible with qcom,ufshc and if not found
  fall back to expecting this was a eMMC only DTB?

* Display panel
  Find the qcom,mdss compatible, follow the qcom,mdp5 compatible child
  to extract ports/port@0 to get the of_graph handle to some connector
  node, then in ../port@1 we can find a phandle to the panel which we
  can find and then match against a predefined set of compatibles.

> At least for 96boards I think we can update the lk bootloaders on
> there to adopt this code. For other platforms like nexus though I
> don't see a way we can update those bootloaders, and those
> bootloaders require these properties exist in the dtbs, so we
> should just throw the numbers into the dts files there and be
> done with post processing. For bootloaders that require the QCDT
> header, we'll have to keep running dtbtool there to generate the
> header. Having the ids in the dts file or not doesn't really
> matter there.
> 

At the time we introduced the Xperia Z1 (Honami) our boot loader only
supported QCDT, so I experimented with a version of dtbTool that kept a
compatible to id table mapping hardcoded (very much like your existing
dtbTool). And as expected it turns into an unmaintainable mess to track
this information on the side.


I'm sorry, but to me that just sounds like a lot of work to find an
alternative to the functional and pragmatic solution that exists today,
just for the sake of hiding these non-standard ids in an even more
non-standard way.

Regards,
Bjorn