[U-Boot] [PATCH 01/11] imx: Add bootcmd to load and run UEFI from mmc

[Henry Beberman]

> -----Original Message-----
> From: Trent Piepho <tpiepho at impinj.com>
> Sent: Tuesday, July 17, 2018 10:24 AM
> To: Henry Beberman <Henry.Beberman at microsoft.com>; u-
> boot at lists.denx.de
> Cc: trini at konsulko.com; fabio.estevam at nxp.com
> Subject: Re: [U-Boot] [PATCH 01/11] imx: Add bootcmd to load and run UEFI
> from mmc
> 
> On Mon, 2018-07-16 at 23:56 +0000, Henry Beberman wrote:
> > >
> > > >
> > > > I need to revise the commit message for this patch. The script is
> > > > not fixed
> > >
> > > to the first partition of the selected MMC, it scans the disk for
> > > partitions marked bootable, then checks each one of those until it
> > > finds the imxboard_efi.fd binary.
> > >
> > > That is indeed very different from first FAT partition.  Does
> > > bootable only apply legacy MBR partition tables?  I didn't think
> > > bootable was typically used with GPT tables.  There is a bit, but it's not
> used to mark EFI partitions.
> > >
> > > Which brings me back to the partition type.  Isn't that the right
> > > way to find the EFI?
> >
> > The is_bootable function in disk/part_efi.c marks a partition as bootable if
> the partition_type_guid on disk matches the EFI PARTITION_SYSTEM_GUID.
> > The part command with the -bootable flag will return the EFI partition
> > on both GPT and MBR partition schemes. This method is also used by
> > config_distro_bootcmd.h
> 
> But it also finds any partitions with the legacy bios bootable flag set in a GPT
> table or the active partition bit set in a MBR table, or any future reason a
> partition might be considered bootable.  Someone trying to add a new type
> of bootable partition to distro bootcmd will be forced to deal with your
> windows nt boot command as it tries to boot any bootable partition, even
> ones it can't boot.
> 
> The distro boot command is designed to boot anything, so it searches for
> partitions beyond EFI.  But what you've done is just for EFI.
> That's why it's different.

It doesn’t matter if someone adds a new type of bootable partition in the future, the UEFI boot command will fail to find the imxboard_efi.fd binary then move along to check the next bootable partition.

Adding this boot command will not increase maintenance on config_distro_bootcmd.h. The UEFI boot command is only used when the defconfig selects CONFIG_UEFI_BOOT, and the board's include/configs header has been modified to include config_uefi_bootcmd.h instead of config_distro_bootcmd.h when the config is set.