[U-Boot] [PATCH] config_distro_bootcmd.h: add note on error handling

[Simon Glass]

On 10 March 2015 at 15:40, Stephen Warren <swarren at wwwdotorg.org> wrote:
> From: Stephen Warren <swarren at nvidia.com>
>
> This should make it more clear why there appear to be C pre-processor
> symbols in the file that contain mixed case. They're really error
> messages.
>
> Suggested-by: Simon Glass <sjg at chromium.org>
> Signed-off-by: Stephen Warren <swarren at nvidia.com>
> ---
>  include/config_distro_bootcmd.h | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/include/config_distro_bootcmd.h b/include/config_distro_bootcmd.h
> index 07a0b3b23472..73f093f9eaf5 100644
> --- a/include/config_distro_bootcmd.h
> +++ b/include/config_distro_bootcmd.h
> @@ -10,6 +10,22 @@
>  #ifndef _CONFIG_CMD_DISTRO_BOOTCMD_H
>  #define _CONFIG_CMD_DISTRO_BOOTCMD_H
>
> +/*
> + * A note on error handling: It is possible for BOOT_TARGET_DEVICES to
> + * reference a device that is not enabled in the U-Boot configuration, e.g.
> + * it may include MMC in the list without CONFIG_CMD_MMC being enabled. Given
> + * that BOOT_TARGET_DEVICES is a macro that's expanded by the C pre-processor
> + * at compile time, it's not  possible to detect and report such problems via
> + * a simple #ifdef/#error combination. Still, the code needs to report errors.
> + * The best way I've found to do this is to make BOOT_TARGET_DEVICES expand to
> + * reference a non-existent symbol, and have the name of that symbol encode
> + * the error message. Consequently, this file contains references to e.g.
> + * BOOT_TARGET_DEVICES_references_MMC_without_CONFIG_CMD_MMC. Given the
> + * prevalence of capitals here, this looks like a pre-processor macro and
> + * hence seems like it should be all capitals, but it's really an error
> + * message that includes some other pre-processor symbols in the text.
> + */
> +
>  /* We need the part command */
>  #define CONFIG_PARTITION_UUIDS
>  #define CONFIG_CMD_PART

Very clear thank you.

Reviewed-by: Simon Glass <sjg at chromium.org>