Re: [PATCH 3/3] commands: add of_bootargs command.

[Roland Hieber <rhi@pengutronix.de>]

On Thu, Feb 21, 2019 at 10:28:48AM +0100, Tomaz Solc wrote:
> When booting a Raspberry Pi, it is useful to extract bootargs from the
> device tree that was created by the VideoCore firmware. These bootargs
> contain for example settings for the framebuffer that the kernel needs
> to properly set the video output.
> 
> This commit adds an of_bootargs command that extracts a bootargs
> property from a device tree and saves it to a global variable.
> 
> For example, a bootloader environment can use this command to extract
> the bootargs to linux.bootargs.vc, which then gets included into the
> final bootargs for the kernel using CONFIG_FLEXIBLE_BOOTARGS.
> ---
>  Documentation/boards/bcm2835.rst |  4 ++
>  commands/Kconfig                 | 13 ++++++
>  commands/Makefile                |  1 +
>  commands/of_bootargs.c           | 99 ++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 117 insertions(+)
>  create mode 100644 commands/of_bootargs.c
> 
> diff --git a/Documentation/boards/bcm2835.rst b/Documentation/boards/bcm2835.rst
> index 95e910896..b8a6c18ea 100644
> --- a/Documentation/boards/bcm2835.rst
> +++ b/Documentation/boards/bcm2835.rst
> @@ -34,5 +34,9 @@ VideoCore firmware creates a device tree based on the entries in ``config.txt``.
>  
>      bootm -o /vc.dtb /boot/kernel7.img
>  
> +VideoCore device tree also contains the kernel command-line that is constructed from ``cmdline.txt`` and other parameters internally determined by the VideoCore firmware. Normally in Barebox this command-line gets overwritten by the Linux bootargs (see :ref:`booting_linux`). You can extract the VideoCore command-line from the device tree using the following command::
> +
> +    of_bootargs /vc.dtb linux.bootargs.vc
> +
>  .. _Raspberry Pi firmware: https://codeload.github.com/raspberrypi/firmware/zip/80e1fbeb78f9df06701d28c0ed3a3060a3f557ef
>  .. _documentation for config.txt: https://www.raspberrypi.org/documentation/configuration/config-txt/
> diff --git a/commands/Kconfig b/commands/Kconfig
> index c14332c9d..0ae6d526f 100644
> --- a/commands/Kconfig
> +++ b/commands/Kconfig
> @@ -2015,6 +2015,19 @@ config CMD_OF_DUMP
>  	  Options:
>  		-f <dtb>	work on <dtb> instead of internal devicetree
>  
> +config CMD_OF_BOOTARGS
> +	tristate
> +	select OFTREE
> +	prompt "of_bootargs"
> +	help
> +	  Extract bootargs from a device tree into a global variable
> +
> +	  Usage: of_bootargs [DTB] [VAR]
> +
> +	  DTB is path to a device tree file (e.g. /vc.dtb).
> +	  VAR is a name of the global variable to set (e.g. linux.bootargs.vc)
> +
> +
>  config CMD_OF_NODE
>  	tristate
>  	select OFTREE
> diff --git a/commands/Makefile b/commands/Makefile
> index 358671bb5..f554f6041 100644
> --- a/commands/Makefile
> +++ b/commands/Makefile
> @@ -76,6 +76,7 @@ obj-$(CONFIG_CMD_OFTREE)	+= oftree.o
>  obj-$(CONFIG_CMD_OF_PROPERTY)	+= of_property.o
>  obj-$(CONFIG_CMD_OF_NODE)	+= of_node.o
>  obj-$(CONFIG_CMD_OF_DUMP)	+= of_dump.o
> +obj-$(CONFIG_CMD_OF_BOOTARGS)	+= of_bootargs.o
>  obj-$(CONFIG_CMD_OF_DISPLAY_TIMINGS)	+= of_display_timings.o
>  obj-$(CONFIG_CMD_OF_FIXUP_STATUS)	+= of_fixup_status.o
>  obj-$(CONFIG_CMD_MAGICVAR)	+= magicvar.o
> diff --git a/commands/of_bootargs.c b/commands/of_bootargs.c
> new file mode 100644
> index 000000000..93e7b74b1
> --- /dev/null
> +++ b/commands/of_bootargs.c
> @@ -0,0 +1,99 @@
> +/*
> + * of_dump.c - dump devicetrees to the console
> + *
> + * Copyright (c) 2014 Sascha Hauer <s.hauer@pengutronix.de>, Pengutronix

Is this true? :-)

And please add a SPDX-License-Identifier to the new files. See [9] for
an explanation (and replace "Linux" by "barebox" in your head when
reading it :))

[9]: https://www.kernel.org/doc/html/latest/process/license-rules.html

> + *
> + * See file CREDITS for list of people who contributed to this
> + * project.

Leave out this paragraph, that file does not exist.

 - Roland

> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2
> + * as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + */
> +
> +#include <common.h>
> +#include <libfile.h>
> +#include <of.h>
> +#include <command.h>
> +#include <malloc.h>
> +#include <complete.h>
> +#include <linux/ctype.h>
> +#include <errno.h>
> +#include <linux/err.h>
> +#include <globalvar.h>
> +
> +static int do_of_bootargs(int argc, char *argv[])
> +{
> +	int ret = 0;
> +	struct device_node *root = NULL, *node;
> +	char *dtbfile, *varname;
> +	void *fdt;
> +
> +	size_t size;
> +	const char *cmdline;
> +
> +	if (argc != 3) {
> +		return COMMAND_ERROR_USAGE;
> +	}
> +
> +	dtbfile = argv[1];
> +	varname = argv[2];
> +
> +	fdt = read_file(dtbfile, &size);
> +	if (!fdt) {
> +		printf("unable to read %s: %s\n", dtbfile, strerror(errno));
> +		return -errno;
> +	}
> +
> +	root = of_unflatten_dtb(fdt);
> +
> +	free(fdt);
> +
> +	if (IS_ERR(root)) {
> +		ret = PTR_ERR(root);
> +		root = NULL;
> +		goto out;
> +	}
> +
> +	node = of_find_node_by_path_from(root, "/chosen");
> +	if (!node) {
> +		printf("no /chosen node\n");
> +		ret = -ENOENT;
> +		goto out;
> +	}
> +
> +	cmdline = of_get_property(node, "bootargs", NULL);
> +	if (!cmdline) {
> +		printf("no bootargs property in the /chosen node\n");
> +		ret = -ENOENT;
> +		goto out;
> +	}
> +
> +	globalvar_add_simple(varname, cmdline);
> +
> +out:
> +	if (root)
> +		of_delete_node(root);
> +
> +	return ret;
> +}
> +
> +BAREBOX_CMD_HELP_START(of_bootargs)
> +BAREBOX_CMD_HELP_TEXT("DTB is path to a device tree file (e.g. /vc.dtb).")
> +BAREBOX_CMD_HELP_TEXT("VAR is a name of the global variable to set (e.g. linux.bootargs.vc)")
> +BAREBOX_CMD_HELP_END
> +
> +BAREBOX_CMD_START(of_bootargs)
> +	.cmd		= do_of_bootargs,
> +	BAREBOX_CMD_DESC("extract bootargs from a device tree into a global variable")
> +	BAREBOX_CMD_OPTS("[DTB] [VAR]")
> +	BAREBOX_CMD_GROUP(CMD_GRP_MISC)
> +	BAREBOX_CMD_COMPLETE(devicetree_file_complete)
> +	BAREBOX_CMD_HELP(cmd_of_bootargs_help)
> +BAREBOX_CMD_END
> -- 
> 2.11.0
> 
> 
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-- 
Roland Hieber                     | r.hieber@pengutronix.de     |
Pengutronix e.K.                  | https://www.pengutronix.de/ |
Peiner Str. 6-8, 31137 Hildesheim | Phone: +49-5121-206917-5086 |
Amtsgericht Hildesheim, HRA 2686  | Fax:   +49-5121-206917-5555 |

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