[Buildroot] [PATCH v7] board: add support for Intel Galileo Gen 2

[Kinsella, Ray <ray.kinsella@intel.com>]

ignore this - in working out my reasoning below, I have worked out an
alternative that allows the consolidation into a single file.

Ray K

On Mon, 2015-11-16 at 17:29 +0000, Kinsella, Ray wrote:
> > > diff --git a/board/intel/galileo/genimage.cfg b/board/intel/galileo/genimage.cfg
> > > new file mode 100644
> > > index 0000000..b1db6f7
> > > --- /dev/null
> > > +++ b/board/intel/galileo/genimage.cfg
> > > @@ -0,0 +1,15 @@
> > > +image sdcard.img {
> > > +	hdimage {
> > > +	}
> > > +
> > > +	partition boot {
> > > +		partition-type = 0xC
> > > +		image = "efi-part.vfat"
> > 
> >  Doesn't genimage allow to specify this in a single file?
> 
> Hi Arnout, 
> 
> Needed to do a bit of investigation to refresh my memory here - on why I
> implemented this way. To understand what genimage does requires a bit of
> understanding of what tools it is using under the hood. Typically using
> hdimage and vfat are mutually exclusive.
> 
>  * hdimage - typically I use hdimage where I have 1 or more partitions I
> want to aggregate into a single image ... so I want pull the ext3/ext4
> image created by buildroot as a partition. 
>  * vfat - typically I use vfat where I want to use an overlay fs, i.e. a
> sdcard that has been formatted as vfat with a EFI, Kernel, Ext3 overlay
> image and perhaps also an initramfs. 
> 
> So you are usually doing one or the other. The constraint with Galileo
> Gen 2 is that it's UEFI BIOS can only read VFAT or EFI partitions when
> looking for bootloader EFI binaries like grub-efi or gummiboot. So this
> leaves me with a couple of options:-
> 
>  * I can use hdimage - I can create the VFAT/EFI partition myself
> calling mtools, and then use hdimage above to aggregate this partition
> into an image along with the rootfs image produced by buildroot
>  * I can use vfat with the overlay fs approach, however this typically
> comes with a boottime performance penalty.
> 
> So my approach is as follows ...
> 
>  * Use genimage vfat instead to create my first 'image' as vfat, under
> the hood genimage uses dd + mkfs.vfat to create the image and then uses
> mtools (mmd + mcopy) to copy in the EFI binaries.
>  * I then use hdimage to pull in the vfat image above as an EFI parition
> and the ext3 image created by buildroot as the rootfs partition. 
> 
> For me this was simplest approach to layout the sdcard image as the
> Galileo requires, much simpler than rewriting lots of mtools logic that
> already exists in genimage. Make sense ?
> 
> Ray K
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