[PATCH 01/14] qemu: arm: Use the generated DTB only when CONGIG_OF_BOARD is defined

[Heinrich Schuchardt]

On 08.12.20 06:28, Sughosh Ganu wrote:
>
> On Mon, 7 Dec 2020 at 23:28, Heinrich Schuchardt <xypron.glpk at gmx.de
> <mailto:xypron.glpk at gmx.de>> wrote:
>
>     On 07.12.20 13:50, Heinrich Schuchardt wrote:
>     > On 07.12.20 06:15, Sughosh Ganu wrote:
>     >> hello Heinrich,
>     >>
>     >> On Sat, 5 Dec 2020 at 15:01, Heinrich Schuchardt
>     <xypron.glpk at gmx.de <mailto:xypron.glpk at gmx.de>
>     >> <mailto:xypron.glpk at gmx.de <mailto:xypron.glpk at gmx.de>>> wrote:
>     >>
>     >>     On 11/26/20 7:40 PM, Sughosh Ganu wrote:
>     >>     > The Qemu platform emulator generates a device tree blob and
>     places it
>     >>     > at the start of the dram, which is then used by u-boot. Use
>     this dtb
>     >>     > only if CONFIG_OF_BOARD is defined. This allows using a
>     different
>     >>     > device tree, using the CONFIG_OF_SEPARATE option. This dtb
>     is attached
>     >>     > to the u-boot binary as a u-boot-fdt.bin file
>     >>
>     >>     Dear Sughosh,
>     >>
>     >>     thank your for this series which will allow us to better
>     demonstrate and
>     >>     test capsule updates.
>     >>
>     >>     I am not sure if the approach that you take at device-trees
>     here is the
>     >>     right one.
>     >>
>     >>     On QEMU the device-tree is generated on the fly by the QEMU
>     binary
>     >>     depending on which devices the user has specified.
>     >>
>     >>     Your idea is to replace this device-tree completely to be
>     able to add
>     >>     extra elements (the EFI signature list, see patch 2/14). Thus a
>     >>     device-tree might be loaded that does not match the user selected
>     >>     devices.
>     >>
>     >>     An alternative approach would be to apply all additions to the
>     >>     device-tree as an FDT overlay (or fixup). This would allow
>     the dynamic
>     >>     parts of the QEMU device-tree still to be passed through.
>     >>
>     >>
>     >> I will take a look at storing the public key as part of the fdt
>     overlay,
>     >> with a runtime fixup. Although, I think the issue that you are
>     pointing
>     >> to would be specific to Qemu and not other platforms. But I do
>     see the
>     >> merit in having the public-key certificate stored as part of an
>     overlay.
>     >> If I hit any issues while implementing this, I will get back to
>     you. Thanks.
>     >>
>     >> -sughosh
>     >
>     > OpenSBI can supply a device-tree to U-Boot. So this would be an
>     > equivalent case.
>     >
>     > Best regards
>     >
>     > Heinrich
>
>     <sng_>: "I am unable to think of a simple and elegant way to generate
>     the overlay dtb, since this would require creation of a corresponding
>     dts file, compiling it into a dtb and then using this on the platform."
>
>     Jean-Jacques' patch series introduced some of the necessary code:
>
>     [PATCH PATCH v6 00/13] Add support for applications of overlays in SPL
>     https://lists.denx.de/pipermail/u-boot/2019-October/387653.html
>     <https://lists.denx.de/pipermail/u-boot/2019-October/387653.html>
>     https://patchwork.ozlabs.org/project/uboot/list/?series=137810&state=%2A&archive=both
>     <https://patchwork.ozlabs.org/project/uboot/list/?series=137810&state=%2A&archive=both>
>
>     CONFIG_OF_OVERLAY_LIST is used to specify the overlays to be compiled.
>     You will have to remove the CONFIG_SPL_LOAD_FIT_APPLY_OVERLAY and
>     CONFIG_SPL_LOAD_FIT dependency.
>
>
> What i meant was that the process to generate the fdt overlay on the
> host, embed it with the public-key certificate is more cumbersome than
> the current solution. So, for comparing the embedding the pub-key cert
> in the fdt overlay, as against the platform dtb
>
> Embedding the certificate in the overlay
> 1) Generate a skeleton overlay dts file
> 2) Convert it to a dtb
> 3) Run it through the mkeficapsule utility to embed the pub-key
> certificate in the overlay(dtb)
> 4) Store the overlay dtb on some nv storage on the platform(ESP partition?)
> 5) Load the overlay and apply it to the platform's dtb
> 6) Retrieve the certificate from the dtb at the time of capsule
> authentication
>
> Embedding the certificate in the platform's dtb
> 1) Run the platform's dtb through the mkeficapsule utility to embed
> the pub-key certificate
> 2) Boot the platform with the platform's dtb
> 3) Retrieve the certificate from the dtb at the time of capsule
> authentication
>
> You had mentioned OpenSBI passing the dtb to u-boot. Does the OpenSBI
> generate the device tree for the platform on the fly even for non-qemu
> platforms. If it does not, the dtb that OpenSBI uses can be run through
> the mkeficapsule utility to embed the certificate.

OpenSBI applies fix-ups before passing the device-tree. The prototype
device-tree can either be built into OpenSBI or can be passed from an
earlier firmware stage.

Best regards

Heinrich

>
> -sughosh