[PATCH v2] cmd: pxe: add support for FDT overlays

[Jernej Škrabec]

Dne ponedeljek, 04. januar 2021 ob 15:41:17 CET je Tom Rini napisal(a):
> On Mon, Jan 04, 2021 at 03:33:43PM +0100, Neil Armstrong wrote:
> > This adds support for specifying FDT overlays in an extlinux/pxelinux
> > configuration file.
> > 
> > Without this, there is no simple way to apply overlays when the kernel
> > and fdt is loaded by the pxe command.
> > 
> > This change adds the 'fdtoverlays' keyword for a label, supporting
> > multiple
> > overlay files to be applied on top of the fdt specified in the 'fdt' or
> > 'devicetree' keyword.
> > 
> > Example:
> >   label linux
> >   
> >     kernel /Image
> >     devicetree /soc-board.dtb

This should be "fdt /soc-board.dtb",

> >     fdtoverlays /soc-board-function.dtbo
> >     append console=ttyS0,115200 root=/dev/mmcblk0p2 rootwait
> > 
> > This code makes usage of a new variable called fdtoverlay_addr_r used to
> > load the overlay files without overwritting anything important.
> > 
> > Cc: Tom Rini <trini at konsulko.com>
> > Cc: Andre Heider <a.heider at gmail.com>
> > Cc: Jernej Škrabec <jernej.skrabec at siol.net>
> > Cc: Jonas Karlman <jonas at kwiboo.se>
> > Signed-off-by: Neil Armstrong <narmstrong at baylibre.com>

Tested-by: Jernej Skrabec <jernej.skrabec at siol.net>

With above fix:
Reviewed-by: Jernej Skrabec <jernej.skrabec at siol.net>

> > ---
> > Hi Tom,
> > 
> > This is repost of my last year's attempt.
> > It fills a hole to allow loading FDT overlays using PXE/Extlinux without
> > using FIT.
> > 
> > V2 adds documentation.
> 
> Thanks for following up.  I assume this follows what the spec says for
> this file?

Which specs? Official extlinux configuration specs [1] don't say anything about 
device tree files, so anything related to that is an extension (I hope I found 
correct specs). I think this one is extremely useful, users can easily specify 
which overlay file(s) they want to be applied in a text file.

Best regards,
Jernej

[1] https://repo.or.cz/syslinux.git/blob/HEAD:/doc/syslinux.txt