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

Neil Armstrong narmstrong at baylibre.com
Tue Jan 5 09:14:24 CET 2021

On 04/01/2021 17:21, Jernej Škrabec wrote:
> 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",

Indeed, thx

>>>     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.

Indeed, it follows the spec by not breaking it and simply extends the already
u-boot specific pxe format.


> Best regards,
> Jernej
> [1] https://repo.or.cz/syslinux.git/blob/HEAD:/doc/syslinux.txt

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