Re: [PATCH] cmd: pxe_utils: Check fdtcontroladdr in label_boot

[Andre Przywara <andre.przywara@arm.com>]

On Thu, 14 Oct 2021 12:24:45 -0600
Simon Glass <sjg@chromium.org> wrote:

Hi Simon,

> On Thu, 14 Oct 2021 at 02:40, Peter Hoyes <peter.hoyes@arm.com> wrote:
> >
> > From: Peter Hoyes <Peter.Hoyes@arm.com>
> >
> > If using OF_CONTROL, fdtcontroladdr is set to the fdt used to configure
> > U-Boot. When using PXE, if no fdt is defined in the menu file, and
> > there is no fdt at fdt_addr, add fall back on fdtcontroladdr too.
> >
> > We are developing board support for the Armv8r64 FVP using
> > config_distro_bootcmd. We are also using OF_BOARD and would like the
> > PXE boot option to default to the fdt provided by board_fdt_blob_setup.
> >
> > Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
> > ---
> >  cmd/pxe_utils.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/cmd/pxe_utils.c b/cmd/pxe_utils.c
> > index 067c24e5ff..8f8e69ca97 100644
> > --- a/cmd/pxe_utils.c
> > +++ b/cmd/pxe_utils.c
> > @@ -556,7 +556,10 @@ static int label_boot(struct cmd_tbl *cmdtp, struct pxe_label *label)
> >          * Scenario 2: If there is an fdt_addr specified, pass it along to
> >          * bootm, and adjust argc appropriately.
> >          *
> > -        * Scenario 3: fdt blob is not available.
> > +        * Scenario 3: If there is an fdtcontroladdr specified, pass it along to
> > +        * bootm, and adjust argc appropriately.
> > +        *
> > +        * Scenario 4: fdt blob is not available.
> >          */
> >         bootm_argv[3] = env_get("fdt_addr_r");
> >
> > @@ -646,6 +649,9 @@ static int label_boot(struct cmd_tbl *cmdtp, struct pxe_label *label)
> >         if (!bootm_argv[3])
> >                 bootm_argv[3] = env_get("fdt_addr");
> >
> > +       if (!bootm_argv[3])
> > +               bootm_argv[3] = env_get("fdtcontroladdr");
> > +
> >         if (bootm_argv[3]) {
> >                 if (!bootm_argv[2])
> >                         bootm_argv[2] = "-";
> > --
> > 2.25.1
> >  
> 
> This is a bit strange as fdtcontroladdr is the control dtb that U-Boot
> uses.

Yes, that is the idea. This DTB should be as good as any, and this is the
last check before giving up on DTs completely, so "U-Boot's DTB" (actually
there is no such thing) is better than none at all. In fact EFI boot does
the very same thing:
https://source.denx.de/u-boot/u-boot/-/blob/master/include/config_distro_bootcmd.h#L144-L148

> Can you not set fdt_addr to that, if you need to? Is it not
> already set to that?

According to doc/README.distro, fdt_addr is reserved for DTBs residing at
a (fixed?) ROM address. We don't really know yet where the DT comes from,
the cleanest seems to be to be passed down from TF-A, in which case this
would definitely not be ROM. board_fdt_blob_setup() knows this address,
and this is what will be written to $fdtcontroladdr.

FWIW, this patch looks good to me.

Cheers,
Andre

> Also, there is a clean-up series for this code outstanding. I will
> send v3 and copy you, if you are able to review it.
> 
> Regards,
> Simon