Re: [PATCH] arm64: dts: qcom: sa8775p: Add new memory map updates to SA8775P

[Brian Masney <bmasney@redhat.com>]

Hi Dmitry,

On Fri, Jan 19, 2024 at 10:35:43PM +0200, Dmitry Baryshkov wrote:
> This kind of change sets a very bad precedent. This way old kernels
> become incompatible with the updated firmware. For me it looks like
> Linux kernel suddenly being unable to boot after the BIOS upgrade.
> Generally memory map updates should be disallowed after the board hits
> the production and the DT is published and merged. There can be other
> users of DT. BSD systems, U-Boot. We spend sensible efforts in making
> sure that DT is an ABI: newer kernel remain compatible with older DT
> files. We expect the same kind of efforts from device manufacturers.
> 
> I think unless there is a good reason, the memory map update should be
> reverted on the Qualcomm side as a breaking change.
> If this kind of update is absolutely necessary, it might be better to
> define a new set of board files utilising the new memory map, marking
> existing DT files as legacy.

This is on a development board that's not in production yet, so
personally I think this change is fine. It's in all of our best
interests to have SoC vendors push their code upstream early, even if
it means that later on we need to make memory map changes like this.

Once this is in production, then I agree with you that changes like
this should be avoided if possible.

Brian