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

[Sughosh Ganu]

hello Heinrich,

On Sat, 5 Dec 2020 at 15:01, Heinrich Schuchardt <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


> Could you, please, assess the pros and cons of the two approaches with
> respect to:
>
> * usability for capsule updates
> * applicability for non-QEMU systems
> * integration of DTB overlays with FIT images for other use cases
>
> Best regards
>
> Heinrich
>
>
> >
> > Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
> > ---
> >   board/emulation/qemu-arm/qemu-arm.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/board/emulation/qemu-arm/qemu-arm.c
> b/board/emulation/qemu-arm/qemu-arm.c
> > index f18f2ed7da..e146d1cc50 100644
> > --- a/board/emulation/qemu-arm/qemu-arm.c
> > +++ b/board/emulation/qemu-arm/qemu-arm.c
> > @@ -89,11 +89,13 @@ int dram_init_banksize(void)
> >       return 0;
> >   }
> >
> > +#if defined(CONFIG_OF_BOARD)
> >   void *board_fdt_blob_setup(void)
> >   {
> >       /* QEMU loads a generated DTB for us at the start of RAM. */
> >       return (void *)CONFIG_SYS_SDRAM_BASE;
> >   }
> > +#endif
> >
> >   void enable_caches(void)
> >   {
> >
>
>