@@ -202,3 +202,106 @@ the following file:
If you echo 0 into it means MAX_JIFFY_OFFSET will be used. The data type
for the timeout is an int.
+
+EFI embedded firmware fallback mechanism
+========================================
+
+On some devices the system's EFI code / ROM may contain an embedded copy
+of firmware for some of the system's integrated peripheral devices and
+the peripheral's Linux device-driver needs to access this firmware.
+
+Device drivers which need such firmware can use the
+firmware_request_platform() function for this, note that this is a
+separate fallback mechanism from the other fallback mechanisms and
+this does not use the sysfs interface.
+
+A device driver which needs this can describe the firmware it needs
+using an efi_embedded_fw_desc struct:
+
+.. kernel-doc:: include/linux/efi_embedded_fw.h
+ :functions: efi_embedded_fw_desc
+
+The EFI embedded-fw code works by scanning all EFI_BOOT_SERVICES_CODE memory
+segments for an eight byte sequence matching prefix; if the prefix is found it
+then does a sha256 over length bytes and if that matches makes a copy of length
+bytes and adds that to its list with found firmwares.
+
+To avoid doing this somewhat expensive scan on all systems, dmi matching is
+used. Drivers are expected to export a dmi_system_id array, with each entries'
+driver_data pointing to an efi_embedded_fw_desc.
+
+To register this array with the efi-embedded-fw code, a driver needs to:
+
+1. Always be builtin to the kernel or store the dmi_system_id array in a
+ separate object file which always gets builtin.
+
+2. Add an extern declaration for the dmi_system_id array to
+ include/linux/efi_embedded_fw.h.
+
+3. Add the dmi_system_id array to the embedded_fw_table in
+ drivers/firmware/efi/embedded-firmware.c wrapped in a #ifdef testing that
+ the driver is being builtin.
+
+4. Add "select EFI_EMBEDDED_FIRMWARE if EFI_STUB" to its Kconfig entry.
+
+The firmware_request_platform() function will always first try to load firmware
+with the specified name directly from the disk, so the EFI embedded-fw can
+always be overridden by placing a file under /lib/firmware.
+
+Note that:
+
+1. The code scanning for EFI embedded-firmware runs near the end
+ of start_kernel(), just before calling rest_init(). For normal drivers and
+ subsystems using subsys_initcall() to register themselves this does not
+ matter. This means that code running earlier cannot use EFI
+ embedded-firmware.
+
+2. At the moment the EFI embedded-fw code assumes that firmwares always start at
+ an offset which is a multiple of 8 bytes, if this is not true for your case
+ send in a patch to fix this.
+
+3. At the moment the EFI embedded-fw code only works on x86 because other archs
+ free EFI_BOOT_SERVICES_CODE before the EFI embedded-fw code gets a chance to
+ scan it.
+
+4. The current brute-force scanning of EFI_BOOT_SERVICES_CODE is an ad-hoc
+ brute-force solution. There has been discussion to use the UEFI Platform
+ Initialization (PI) spec's Firmware Volume protocol. This has been rejected
+ because the FV Protocol relies on *internal* interfaces of the PI spec, and:
+ 1. The PI spec does not define peripheral firmware at all
+ 2. The internal interfaces of the PI spec do not guarantee any backward
+ compatibility. Any implementation details in FV may be subject to change,
+ and may vary system to system. Supporting the FV Protocol would be
+ difficult as it is purposely ambiguous.
+
+Example how to check for and extract embedded firmware
+------------------------------------------------------
+
+To check for, for example Silead touchscreen controller embedded firmware,
+do the following:
+
+1. Boot the system with efi=debug on the kernel commandline
+
+2. cp /sys/kernel/debug/efi/boot_services_code? to your home dir
+
+3. Open the boot_services_code? files in a hex-editor, search for the
+ magic prefix for Silead firmware: F0 00 00 00 02 00 00 00, this gives you
+ the beginning address of the firmware inside the boot_services_code? file.
+
+4. The firmware has a specific pattern, it starts with a 8 byte page-address,
+ typically F0 00 00 00 02 00 00 00 for the first page followed by 32-bit
+ word-address + 32-bit value pairs. With the word-address incrementing 4
+ bytes (1 word) for each pair until a page is complete. A complete page is
+ followed by a new page-address, followed by more word + value pairs. This
+ leads to a very distinct pattern. Scroll down until this pattern stops,
+ this gives you the end of the firmware inside the boot_services_code? file.
+
+5. "dd if=boot_services_code? of=firmware bs=1 skip=<begin-addr> count=<len>"
+ will extract the firmware for you. Inspect the firmware file in a
+ hexeditor to make sure you got the dd parameters correct.
+
+6. Copy it to /lib/firmware under the expected name to test it.
+
+7. If the extracted firmware works, you can use the found info to fill an
+ efi_embedded_fw_desc struct to describe it, run "sha256sum firmware"
+ to get the sha256sum to put in the sha256 field.
@@ -12,6 +12,8 @@ a driver issues a firmware API call.
return it immediately
* The ''Direct filesystem lookup'' is performed next, if found we
return it immediately
+* The ''Platform firmware fallback'' is performed next, but only when
+ firmware_request_platform() is used, if found we return it immediately
* If no firmware has been found and the fallback mechanism was enabled
the sysfs interface is created. After this either a kobject uevent
is issued or the custom firmware loading is relied upon for firmware
@@ -25,6 +25,11 @@ firmware_request_nowarn
.. kernel-doc:: drivers/base/firmware_loader/main.c
:functions: firmware_request_nowarn
+firmware_request_platform
+-------------------------
+.. kernel-doc:: drivers/base/firmware_loader/main.c
+ :functions: firmware_request_platform
+
request_firmware_direct
-----------------------
.. kernel-doc:: drivers/base/firmware_loader/main.c
@@ -5,5 +5,6 @@ obj-$(CONFIG_FW_LOADER_USER_HELPER) += fallback_table.o
obj-$(CONFIG_FW_LOADER) += firmware_class.o
firmware_class-objs := main.o
firmware_class-$(CONFIG_FW_LOADER_USER_HELPER) += fallback.o
+firmware_class-$(CONFIG_EFI_EMBEDDED_FIRMWARE) += fallback_platform.o
obj-y += builtin/
@@ -66,4 +66,14 @@ static inline void unregister_sysfs_loader(void)
}
#endif /* CONFIG_FW_LOADER_USER_HELPER */
+#ifdef CONFIG_EFI_EMBEDDED_FIRMWARE
+int firmware_fallback_platform(struct fw_priv *fw_priv, enum fw_opt opt_flags);
+#else
+static inline int firmware_fallback_platform(struct fw_priv *fw_priv,
+ enum fw_opt opt_flags)
+{
+ return -ENOENT;
+}
+#endif
+
#endif /* __FIRMWARE_FALLBACK_H */
new file mode 100644
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/efi_embedded_fw.h>
+#include <linux/property.h>
+#include <linux/security.h>
+#include <linux/vmalloc.h>
+
+#include "fallback.h"
+#include "firmware.h"
+
+int firmware_fallback_platform(struct fw_priv *fw_priv, enum fw_opt opt_flags)
+{
+ int rc;
+
+ if (!(opt_flags & FW_OPT_FALLBACK_PLATFORM))
+ return -ENOENT;
+
+ rc = security_kernel_load_data(LOADING_FIRMWARE_EFI_EMBEDDED);
+ if (rc)
+ return rc;
+
+ rc = efi_get_embedded_fw(fw_priv->fw_name, &fw_priv->data,
+ &fw_priv->size);
+ if (rc)
+ return rc; /* rc == -ENOENT when the fw was not found */
+
+ fw_state_done(fw_priv);
+ return 0;
+}
@@ -29,6 +29,9 @@
* firmware caching mechanism.
* @FW_OPT_NOFALLBACK_SYSFS: Disable the sysfs fallback mechanism. Takes
* precedence over &FW_OPT_UEVENT and &FW_OPT_USERHELPER.
+ * @FW_OPT_FALLBACK_PLATFORM: Enable fallback to device fw copy embedded in
+ * the platform's main firmware. If both this fallback and the sysfs
+ * fallback are enabled, then this fallback will be tried first.
*/
enum fw_opt {
FW_OPT_UEVENT = BIT(0),
@@ -37,6 +40,7 @@ enum fw_opt {
FW_OPT_NO_WARN = BIT(3),
FW_OPT_NOCACHE = BIT(4),
FW_OPT_NOFALLBACK_SYSFS = BIT(5),
+ FW_OPT_FALLBACK_PLATFORM = BIT(6),
};
enum fw_status {
@@ -776,6 +776,9 @@ _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,
@@ -883,6 +886,30 @@ 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
@@ -44,6 +44,8 @@ int request_firmware(const struct firmware **fw, const char *name,
struct device *device);
int firmware_request_nowarn(const struct firmware **fw, const char *name,
struct device *device);
+int firmware_request_platform(const struct firmware **fw, const char *name,
+ struct device *device);
int request_firmware_nowait(
struct module *module, bool uevent,
const char *name, struct device *device, gfp_t gfp, void *context,
@@ -69,6 +71,13 @@ static inline int firmware_request_nowarn(const struct firmware **fw,
return -EINVAL;
}
+static inline int firmware_request_platform(const struct firmware **fw,
+ const char *name,
+ struct device *device)
+{
+ return -EINVAL;
+}
+
static inline int request_firmware_nowait(
struct module *module, bool uevent,
const char *name, struct device *device, gfp_t gfp, void *context,
@@ -2964,6 +2964,7 @@ extern int do_pipe_flags(int *, int);
id(UNKNOWN, unknown) \
id(FIRMWARE, firmware) \
id(FIRMWARE_PREALLOC_BUFFER, firmware) \
+ id(FIRMWARE_EFI_EMBEDDED, firmware) \
id(MODULE, kernel-module) \
id(KEXEC_IMAGE, kexec-image) \
id(KEXEC_INITRAMFS, kexec-initramfs) \