[PATCH 00/21] Qualcomm generic board support

[Ilias Apalodimas]

Hi Caleb,

Late to the party, but I'll respond to as much as I can

On Tue, 21 Nov 2023 at 19:09, Caleb Connolly <caleb.connolly at linaro.org> wrote:
>
> Historically, Qualcomm boards in U-Boot have all had their own
> board/qualcomm/xyz directory, their own CONFIG_TARGET_XYZ option, their
> own hardcoded sysmap-xyz.c file, and their own U-Boot specific
> devicetree with little/no compatibility with upstream DT.
>
> This series makes a few final prepatory changes, and then replaces
> almost all of the board specific code with generic alternatives. The end
> result is that all Qualcomm boards both current and future (with the
> exception of the db410c and db820c) can be supported by a single U-Boot
> binary by just providing the correct DT. New boards can be added without
> introducing any addition mach/ or board/ code or config options.
>
> Due to the nature of this change, the patch ("mach-snapdragon:
> generalise board support") has become pretty big, I tried a few
> different ways to represent this in git history, but the other methods
> (e.g. adding a stub "generic" target and removing it again) were more
> confusing and made for much messier git history. The current patch is
> mostly atomic, but requires regenerating the config.
>
> The QCS404 EVB board had some code to enable the USB VBUS regulator,
> this is dropped in favour of a adding a new vbus-supply property to the
> dwc3-generic driver. This will also be used by the dragonboard845c in a
> future patch. This handles the common case of a board requiring some
> regulator be enabled for USB host mode.
>
> A more detailed description of the changes is below.
>
> == Memory map ==
>
> The memory map was historically hardcoded into U-Boot, this meant that
> U-Boot had to be built for a specific variant of a device. This is
> changed to instead read the memory map from the DT /memory node.
>
> Additionally, most boards mapped addresss 0x0 as valid, as a result if a
> null pointer access happens then it will cause a bus stall (and board
> hang). This is fixed so that null pointer accesses will now correctly
> throw an exception.
>
> == DT loading ==
>
> Previously, boards used the FDT blob embedded into U-Boot (via
> OF_SEPARATE). However, most Qualcomm boards run U-Boot as a secondary
> bootloader, so we can instead rely on the first-stage bootloader to
> populate some useful FDT properties for us (notably the /memory node and
> KASLR seed)

Note that the kaslr-seed is not so useful when booting with EFI.  The
kernel's EFI-stub ignores that and instead tries to randomize the
physical placement of the kernel if it finds an EFI_RNG protocol.

>  and fetch the DTB that it provides. Combined with the memory
> map changes above, this let's us entirely avoid configuring the memory
> map explicitly.

[...]

Cheers
/Ilias