[PATCH] firmware_loader: Add /lib/firmware/vendor paths for Apple ARM platforms

On Apple ARM machines (branded Apple Silicon Macs), there is
non-redistributable firmware provided in macOS that is required
for Linux to leverage the hardware to run properly.

The firmware covers Wi-Fi+BT support, USB, hardware ISP, the touchbar
touchscreen, and the trackpad.

In order to ensure this firmware can be installed without messing
with firmware provided by linux-firmware and other packages that
put things in the tree, the empty "vendor" subdirectory was created
to serve this purpose. This directory is used by the asahi dracut
module as part of the Asahi Linux installation process to transfer
firmware from macOS to the newly installed Linux system.

This is based on the patch originally written by Hector Martin
for Asahi Linux.

Link: https://asahilinux.org/docs/platform/introduction/
Signed-off-by: Neal Gompa <[email protected]>
---
 Documentation/driver-api/firmware/fw_search_path.rst | 2 ++
 drivers/base/firmware_loader/main.c                  | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/Documentation/driver-api/firmware/fw_search_path.rst b/Documentation/driver-api/firmware/fw_search_path.rst
index d7cb1e8f0076..ddd945a47fed 100644
--- a/Documentation/driver-api/firmware/fw_search_path.rst
+++ b/Documentation/driver-api/firmware/fw_search_path.rst
@@ -6,6 +6,8 @@ The following search paths are used to look for firmware on your
 root filesystem.
 
 * fw_path_para - module parameter - default is empty so this is ignored
+* /lib/firmware/vendor/UTS_RELEASE/
+* /lib/firmware/vendor/
 * /lib/firmware/updates/UTS_RELEASE/
 * /lib/firmware/updates/
 * /lib/firmware/UTS_RELEASE/
diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
index 24213a0ea831..1acc5842fb24 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -471,6 +471,8 @@ static int fw_decompress_xz(struct device *dev, struct fw_priv *fw_priv,
 static char fw_path_para[256];
 static const char * const fw_path[] = {
 	fw_path_para,
+	"/lib/firmware/vendor/" UTS_RELEASE,
+	"/lib/firmware/vendor",
 	"/lib/firmware/updates/" UTS_RELEASE,
 	"/lib/firmware/updates",
 	"/lib/firmware/" UTS_RELEASE,
-- 
2.55.0