[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: Monday, July 16, 2018 3:45 PM
> 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 22:28 +0000, Henry Beberman wrote:
> > Hi Trent,
> >
> > > -----Original Message-----
> > > From: Trent Piepho <tpiepho at impinj.com>
> > > Sent: Monday, July 16, 2018 10:17 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 Sat, 2018-07-14 at 00:11 +0000, Henry Beberman wrote:
> > > > From: Henry Beberman <henry.beberman at microsoft.com>
> > > >
> > > > This patch enables i.MX platforms to easily add a boot script to
> > > > their U-Boot Proper environment to automatically load and execute
> > > > an EFI firmware from the first FAT partition of an MMC device.
> > >
> > > Is there a reason to force the first partition instead of using the
> > > EFI partition code to select which partition to boot?
> > >
> > > I also wonder, on a Linux system, is there a reason the EFI
> > > partition must use FAT?
> >
> > 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

> 
> > We could switch over to using the generic load from
> CONFIG_CMD_FS_GENERIC if there's demand for non-FAT filesystems.
> We're currently using fatload because the EFI partitions in our Windows
> images are always FAT formatted.
> 
> You're original search method required the partition be FAT.

I'm happy to switch from the fatload command over to the load command if it will make CONFIG_UEFI_BOOT more widely useful.