firmware: Add new platform fallback mechanism and firmware_request_platform()

In some cases the platform's main firmware (e.g. the UEFI fw) may contain
an embedded copy of device firmware which needs to be (re)loaded into the
peripheral. Normally such firmware would be part of linux-firmware, but in
some cases this is not feasible, for 2 reasons:

1) The firmware is customized for a specific use-case of the chipset / use
with a specific hardware model, so we cannot have a single firmware file
for the chipset. E.g. touchscreen controller firmwares are compiled
specifically for the hardware model they are used with, as they are
calibrated for a specific model digitizer.

2) Despite repeated attempts we have failed to get permission to
redistribute the firmware. This is especially a problem with customized
firmwares, these get created by the chip vendor for a specific ODM and the
copyright may partially belong with the ODM, so the chip vendor cannot
give a blanket permission to distribute these.

This commit adds a new platform fallback mechanism to the firmware loader
which will try to lookup a device fw copy embedded in the platform's main
firmware if direct filesystem lookup fails.

Drivers which need such embedded fw copies can enable this fallback
mechanism by using the new firmware_request_platform() function.

Note that for now this is only supported on EFI platforms and even on
these platforms firmware_fallback_platform() only works if
CONFIG_EFI_EMBEDDED_FIRMWARE is enabled (this gets selected by drivers
which need this), in all other cases firmware_fallback_platform() simply
always returns -ENOENT.

Reported-by: Dave Olsthoorn <dave@bewaar.me>
Suggested-by: Peter Jones <pjones@redhat.com>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20200115163554.101315-5-hdegoede@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 27 insertions, 0 deletions

diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
index 59d1dc322080..76f79913916d 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -778,6 +778,9 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
 						 fw_decompress_xz);
 #endif
 
+	if (ret == -ENOENT)
+		ret = firmware_fallback_platform(fw->priv, opt_flags);
+
 	if (ret) {
 		if (!(opt_flags & FW_OPT_NO_WARN))
 			dev_warn(device,
@@ -886,6 +889,30 @@ int request_firmware_direct(const struct firmware **firmware_p,
 EXPORT_SYMBOL_GPL(request_firmware_direct);
 
 /**
+ * firmware_request_platform() - request firmware with platform-fw fallback
+ * @firmware: pointer to firmware image
+ * @name: name of firmware file
+ * @device: device for which firmware is being loaded
+ *
+ * This function is similar in behaviour to request_firmware, except that if
+ * direct filesystem lookup fails, it will fallback to looking for a copy of the
+ * requested firmware embedded in the platform's main (e.g. UEFI) firmware.
+ **/
+int firmware_request_platform(const struct firmware **firmware,
+			      const char *name, struct device *device)
+{
+	int ret;
+
+	/* Need to pin this module until return */
+	__module_get(THIS_MODULE);
+	ret = _request_firmware(firmware, name, device, NULL, 0,
+				FW_OPT_UEVENT | FW_OPT_FALLBACK_PLATFORM);
+	module_put(THIS_MODULE);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(firmware_request_platform);
+
+/**
  * firmware_request_cache() - cache firmware for suspend so resume can use it
  * @name: name of firmware file
  * @device: device for which firmware should be cached for