[PATCH] USB: gadget: fastboot: introduce optional flag for fastboot partitions

[Sascha Hauer]

On Thu, Sep 22, 2022 at 09:27:23AM +0200, Johannes Zink wrote:
> On some boards, some partitions exposed to fastboot may become
> unavailable under certain circumstances, e.g. if an SD-Card exposed to
> fastboot is removed.
> 
> Previously, this lead to an error and the fastboot gadget did not
> initialize the remaining partitions exposed via fastboot, e.g. an
> eMMC which usually is permanently soldered on the board.
> 
> This patch allows to append an optional flag 'o' to the description of a
> fastboot partition. If this partition is unavailable at the
> initialization of the fastboot gadget, said partition is skipped, while
> the remaining available partitions are still exposed.
> 
> Signed-off-by: Johannes Zink <j.zink at pengutronix.de>
> ---
>  Documentation/user/usb.rst | 1 +
>  common/fastboot.c          | 6 +++++-
>  common/file-list.c         | 3 +++
>  include/file-list.h        | 1 +
>  4 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/user/usb.rst b/Documentation/user/usb.rst
> index 2479efe9d6..f2f57ead98 100644
> --- a/Documentation/user/usb.rst
> +++ b/Documentation/user/usb.rst
> @@ -65,6 +65,7 @@ Several **flags** are supported, each denoted by a single character:
>  * ``r`` Readback. The partition is allowed to be read back (DFU specific)
>  * ``c`` The file shall be created if it doesn't exist. Needed when a regular file is exported.
>  * ``u`` The partition is a MTD device and shall be flashed with a UBI image.
> +* ``o`` The partition is optional, i.e. if it is not available at initialization time, it is skipped instead of aborting the initialization
>  
>  Example:
>  
> diff --git a/common/fastboot.c b/common/fastboot.c
> index 330a06f5a3..6bd1191325 100644
> --- a/common/fastboot.c
> +++ b/common/fastboot.c
> @@ -177,7 +177,11 @@ int fastboot_generic_init(struct fastboot *fb, bool export_bbu)
>  	file_list_for_each_entry(fb->files, fentry) {
>  		ret = fastboot_add_partition_variables(fb, fentry);
>  		if (ret)
> -			return ret;
> +			if((fentry->flags & FILE_LIST_FLAG_OPTIONAL))
> +				pr_info("failed to add optional partition %s to fastboot gadget\n",
> +					fentry->filename);
> +			else
> +				return ret;

I would prefer to check the FILE_LIST_FLAG_OPTIONAL flag in
fastboot_add_partition_variables(). That gives us the possibility to
explicitly check for the right conditions rather than generalising
all possible errors from fastboot_add_partition_variables().

Sascha


-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |