[PATCH 01/14] qemu: arm: Use the generated DTB only when CONGIG_OF_BOARD is defined
Sughosh Ganu
sughosh.ganu at linaro.org
Tue Dec 15 12:10:54 CET 2020
On Wed, 9 Dec 2020 at 03:24, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
> On 12/8/20 10:19 AM, Sughosh Ganu wrote:
> >
> > On Tue, 8 Dec 2020 at 14:32, Heinrich Schuchardt <xypron.glpk at gmx.de
> > <mailto:xypron.glpk at gmx.de>> wrote:
> >
> > 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>
> > > <mailto: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>>
> > > >> <mailto: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://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
> >
> > >
> > <
> 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.
> >
> >
> > So, if qemu if the only platform where the device tree is generated on
> > the fly, and passed along, based on the comparison that i have stated
> > above for the two scenarios(overlay vs platform dtb), I feel that using
> > the platform's dtb and embedding the certificate is more easier to use
> > than using the overlay.
> >
> > Even on the qemu platform, I retrieved the dtb from the platform, for
> > the given set of devices and interfaces used, and then ran the dtb
> > through the mkeficapsule utility.
> >
> > -sughosh
>
> As I understand the whole series is not about productive firmware
> updates for QEMU but about a demonstration how it could be used and
> allowing testing.
>
> Wouldn't it be the enough for testing to apply an overlay with the
> public key using the fdt command?
Is there a way I can build qemu such that the device-tree that is generated
is with the __symbols__ node. Without this node, I am unable to apply the
fdt overlay on the base platform devicetree.
-sughosh
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