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firmware_loader: document firmware_sysfs_fallback()

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This also sets the expecations for future fallback interfaces, even
if they are not exported.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Luis R. Rodriguez 2018-05-10 13:08:40 -07:00 committed by Greg Kroah-Hartman
parent cf1cde7cd6
commit 84b5c4fec7
1 changed files with 20 additions and 0 deletions
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20
drivers/base/firmware_loader/fallback.c
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@ -662,6 +662,26 @@ static bool fw_run_sysfs_fallback(enum fw_opt opt_flags)
return fw_force_sysfs_fallback(opt_flags);
}
/**
* firmware_fallback_sysfs() - use the fallback mechanism to find firmware
* @fw: pointer to firmware image
* @name: name of firmware file to look for
* @device: device for which firmware is being loaded
* @opt_flags: options to control firmware loading behaviour
* @ret: return value from direct lookup which triggered the fallback mechanism
*
* This function is called if direct lookup for the firmware failed, it enables
* a fallback mechanism through userspace by exposing a sysfs loading
* interface. Userspace is in charge of loading the firmware through the syfs
* loading interface. This syfs fallback mechanism may be disabled completely
* on a system by setting the proc sysctl value ignore_sysfs_fallback to true.
* If this false we check if the internal API caller set the @FW_OPT_NOFALLBACK
* flag, if so it would also disable the fallback mechanism. A system may want
* to enfoce the sysfs fallback mechanism at all times, it can do this by
* setting ignore_sysfs_fallback to false and force_sysfs_fallback to true.
* Enabling force_sysfs_fallback is functionally equivalent to build a kernel
* with CONFIG_FW_LOADER_USER_HELPER_FALLBACK.
**/
int firmware_fallback_sysfs(struct firmware *fw, const char *name,
struct device *device,
enum fw_opt opt_flags,