[PATCH v4 2/2] firmware: add DECLARE_FW_CUSTOM_FALLBACK() annotation

[Luis R. Rodriguez]

We need to ensure that when driver developers use the custom firmware
fallback mechanism it was not a copy and paste bug. These use cases on
upstream drivers are rare, we only have 2 upstream users and its for
really old drivers. Since valid uses are rare but possible enable a
white-list for its use, and use this same white-list annotation to refer
to the documentation covering the custom use case.

New faulty users can be reported via 0-day now.

v2: change dependencies on rules make more sense, and fixed
    context mode

Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>
Cc: Richard Purdie <rpurdie@xxxxxxxxx>
Cc: Jacek Anaszewski <j.anaszewski@xxxxxxxxxxx>
Cc: linux-leds@xxxxxxxxxxxxxxx
Cc: Abhay Salunke <Abhay_Salunke@xxxxxxxx>
Acked-by: Jacek Anaszewski <j.anaszewski@xxxxxxxxxxx>
Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
---
 Documentation/driver-api/firmware/fallback-mechanisms.rst     | 7 +++++--
 drivers/firmware/dell_rbu.c                                   | 1 +
 drivers/leds/leds-lp55xx-common.c                             | 1 +
 include/linux/firmware.h                                      | 7 +++++++
 scripts/coccinelle/api/request_firmware-custom-fallback.cocci | 9 ++++++++-
 5 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/Documentation/driver-api/firmware/fallback-mechanisms.rst b/Documentation/driver-api/firmware/fallback-mechanisms.rst
index b87a292153c6..73f509a8d2de 100644
--- a/Documentation/driver-api/firmware/fallback-mechanisms.rst
+++ b/Documentation/driver-api/firmware/fallback-mechanisms.rst
@@ -184,8 +184,11 @@ load firmware for you through a custom path.
 
 The custom fallback mechanism can often be enabled by mistake. We currently
 have only 2 users of it, and little justification to enable it for other users.
-Since it is a common driver developer mistake to enable it, help police for
-new users of the custom fallback mechanism with::
+Since it is a common driver developer mistake to enable it, driver developers
+should use DECLARE_FW_CUSTOM_FALLBACK() to both white-list and validate their
+use and also refer to the documentation for the custom loading solution.
+
+Invalid users of the custom fallback mechanism can be policed using::
 
         $ export COCCI=scripts/coccinelle/api/request_firmware-avoid-init-probe-init.cocci
         $ make coccicheck MODE=report
diff --git a/drivers/firmware/dell_rbu.c b/drivers/firmware/dell_rbu.c
index 2f452f1f7c8a..3f2aa35bc54d 100644
--- a/drivers/firmware/dell_rbu.c
+++ b/drivers/firmware/dell_rbu.c
@@ -586,6 +586,7 @@ static ssize_t read_rbu_image_type(struct file *filp, struct kobject *kobj,
 	return size;
 }
 
+DECLARE_FW_CUSTOM_FALLBACK("Documentation/dell_rbu.txt");
 static ssize_t write_rbu_image_type(struct file *filp, struct kobject *kobj,
 				    struct bin_attribute *bin_attr,
 				    char *buffer, loff_t pos, size_t count)
diff --git a/drivers/leds/leds-lp55xx-common.c b/drivers/leds/leds-lp55xx-common.c
index 5377f22ff994..04161428ee3b 100644
--- a/drivers/leds/leds-lp55xx-common.c
+++ b/drivers/leds/leds-lp55xx-common.c
@@ -219,6 +219,7 @@ static void lp55xx_firmware_loaded(const struct firmware *fw, void *context)
 	release_firmware(chip->fw);
 }
 
+DECLARE_FW_CUSTOM_FALLBACK("Documentation/leds/leds-lp55xx.txt");
 static int lp55xx_request_firmware(struct lp55xx_chip *chip)
 {
 	const char *name = chip->cl->name;
diff --git a/include/linux/firmware.h b/include/linux/firmware.h
index b1f9f0ccb8ac..e6ca19c03dcc 100644
--- a/include/linux/firmware.h
+++ b/include/linux/firmware.h
@@ -8,6 +8,13 @@
 #define FW_ACTION_NOHOTPLUG 0
 #define FW_ACTION_HOTPLUG 1
 
+/*
+ * Helper for scripts/coccinelle/api/request_firmware-custom-fallback.cocci
+ * and so users can also easily search for the documentation for the
+ * respectively needed custom fallback mechanism.
+ */
+#define DECLARE_FW_CUSTOM_FALLBACK(__usermode_helper)
+
 struct firmware {
 	size_t size;
 	const u8 *data;
diff --git a/scripts/coccinelle/api/request_firmware-custom-fallback.cocci b/scripts/coccinelle/api/request_firmware-custom-fallback.cocci
index 0188d446b611..a1ed9d633441 100644
--- a/scripts/coccinelle/api/request_firmware-custom-fallback.cocci
+++ b/scripts/coccinelle/api/request_firmware-custom-fallback.cocci
@@ -15,7 +15,14 @@
 virtual report
 virtual context
 
-@ r1 depends on report || context @
+@ r0 depends on report || context @
+declarer name DECLARE_FW_CUSTOM_FALLBACK;
+expression E;
+@@
+
+DECLARE_FW_CUSTOM_FALLBACK(E);
+
+@ r1 depends on !r0 && (report || context) @
 expression mod, name, dev, gfp, drv, cb;
 position p;
 @@
-- 
2.11.0