Re: [PATCH] ARM: zImage: Allow DTB command line concatenation with ATAG_CMDLINE

[Florian Fainelli <florian@openwrt.org>]

Hello,

On Thursday 21 June 2012 10:56:57 Richard Genoud wrote:
> This patch allows the ATAG_CMDLINE provided by the bootloader to be
> concatenated to the bootargs property of the device tree.
> 
> This is useful to merge static values defined in the device tree with the
> boot loader's (possibly) more dynamic values, such as startup reasons and 
more.
> 
> The bootloader should use the device tree to pass those values to the 
kernel,
> but that's not always simple (old bootloader or very small one).
> 
> The behaviour is the same as the one introduced by Victor Boivie in
> 4394c1244249198c6b85093d46935b761b36ae05 by extending the CONFIG_CMDLINE.

I had a similar need recently, and I was pointed at this more generic 
solution: http://www.mail-archive.com/devicetree-
discuss@lists.ozlabs.org/msg10448.html

The only thing which is ARM-specific and not yet resolved is the following: if 
you have ARM_ATAG_DTB_COMPAT enabled, the kernel command-line contains only 
the bootloader supplied command-line and not bootloader + bootargs from DT. I 
have not yet had a chance to get this sorted.

> 
> Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
> ---
>  arch/arm/Kconfig                        |   19 +++++++++
>  arch/arm/boot/compressed/atags_to_fdt.c |   62 
++++++++++++++++++++++++++++++-
>  2 files changed, 79 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 84449dd..ff4b6e6 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1959,6 +1959,25 @@ config ARM_ATAG_DTB_COMPAT
>  	  bootloaders, this option allows zImage to extract the information
>  	  from the ATAG list and store it at run time into the appended DTB.
>  
> +choice
> +	prompt "Kernel command line type" if ARM_ATAG_DTB_COMPAT
> +	default ARM_ATAG_DTB_COMPAT_CMDLINE_FROM_BOOTLOADER
> +
> +config ARM_ATAG_DTB_COMPAT_CMDLINE_FROM_BOOTLOADER
> +	bool "Use bootloader kernel arguments if available"
> +	help
> +	  Uses the command-line options passed by the boot loader instead of
> +	  the device tree bootargs property. If the boot loader doesn't provide
> +	  any, the device tree bootargs property will be used.
> +
> +config ARM_ATAG_DTB_COMPAT_CMDLINE_EXTEND
> +	bool "Extend with bootloader kernel arguments"
> +	help
> +	  The command-line arguments provided by the boot loader will be
> +	  appended to the the device tree bootargs property.
> +
> +endchoice
> +
>  config CMDLINE
>  	string "Default kernel command string"
>  	default ""
> diff --git a/arch/arm/boot/compressed/atags_to_fdt.c 
b/arch/arm/boot/compressed/atags_to_fdt.c
> index 797f04b..aabc02a 100644
> --- a/arch/arm/boot/compressed/atags_to_fdt.c
> +++ b/arch/arm/boot/compressed/atags_to_fdt.c
> @@ -1,6 +1,12 @@
>  #include <asm/setup.h>
>  #include <libfdt.h>
>  
> +#if defined(CONFIG_ARM_ATAG_DTB_COMPAT_CMDLINE_EXTEND)
> +#define do_extend_cmdline 1
> +#else
> +#define do_extend_cmdline 0
> +#endif
> +
>  static int node_offset(void *fdt, const char *node_path)
>  {
>  	int offset = fdt_path_offset(fdt, node_path);
> @@ -36,6 +42,48 @@ static int setprop_cell(void *fdt, const char *node_path,
>  	return fdt_setprop_cell(fdt, offset, property, val);
>  }
>  
> +static const void *getprop(const void *fdt, const char *node_path,
> +			   const char *property, int *len)
> +{
> +	int offset = fdt_path_offset(fdt, node_path);
> +
> +	if (offset == -FDT_ERR_NOTFOUND)
> +		return NULL;
> +
> +	return fdt_getprop(fdt, offset, property, len);
> +}
> +
> +static void merge_fdt_bootargs(void *fdt, const char *fdt_cmdline)
> +{
> +	char cmdline[COMMAND_LINE_SIZE];
> +	const char *fdt_bootargs;
> +	char *ptr = cmdline;
> +	int len = 0;
> +
> +	/* copy the fdt command line into the buffer */
> +	fdt_bootargs = getprop(fdt, "/chosen", "bootargs", &len);
> +	if (fdt_bootargs)
> +		if (len < COMMAND_LINE_SIZE) {
> +			memcpy(ptr, fdt_bootargs, len);
> +			/* len is the length of the string
> +			 * including the NULL terminator */
> +			ptr += len - 1;
> +		}
> +
> +	/* and append the ATAG_CMDLINE */
> +	if (fdt_cmdline) {
> +		len = strlen(fdt_cmdline);
> +		if (ptr - cmdline + len + 2 < COMMAND_LINE_SIZE) {
> +			*ptr++ = ' ';
> +			memcpy(ptr, fdt_cmdline, len);
> +			ptr += len;
> +		}
> +	}
> +	*ptr = '\0';
> +
> +	setprop_string(fdt, "/chosen", "bootargs", cmdline);
> +}
> +
>  /*
>   * Convert and fold provided ATAGs into the provided FDT.
>   *
> @@ -72,8 +120,18 @@ int atags_to_fdt(void *atag_list, void *fdt, int 
total_space)
>  
>  	for_each_tag(atag, atag_list) {
>  		if (atag->hdr.tag == ATAG_CMDLINE) {
> -			setprop_string(fdt, "/chosen", "bootargs",
> -					atag->u.cmdline.cmdline);
> +			/* Append the ATAGS command line to the device tree
> +			 * command line.
> +			 * NB: This means that if the same parameter is set in
> +			 * the device tree and in the tags, the one from the
> +			 * tags will be chosen.
> +			 */
> +			if (do_extend_cmdline)
> +				merge_fdt_bootargs(fdt,
> +						   atag->u.cmdline.cmdline);
> +			else
> +				setprop_string(fdt, "/chosen", "bootargs",
> +					       atag->u.cmdline.cmdline);
>  		} else if (atag->hdr.tag == ATAG_MEM) {
>  			if (memcount >= sizeof(mem_reg_property)/4)
>  				continue;
> -- 
> 1.7.2.5
> 
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