fw_cfg: add a public uapi header

Create a common header file for well-known values and structures to be
shared by the Linux kernel with qemu or other projects.

It is based from qemu/docs/specs/fw_cfg.txt which references
qemu/include/hw/nvram/fw_cfg_keys.h "for the most up-to-date and
authoritative list" & vmcoreinfo.txt. Those files don't have an
explicit license, but qemu/hw/nvram/fw_cfg.c is BSD-license, so
Michael S. Tsirkin suggested to use the same license.

The patch intentionally left out DMA & vmcoreinfo structures &
defines, which are added in the commits making usage of it.

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

MAINTAINERS

@@ -11368,6 +11368,7 @@ M:	"Michael S. Tsirkin" <mst@redhat.com>
 L:	qemu-devel@nongnu.org
 S:	Maintained
 F:	drivers/firmware/qemu_fw_cfg.c
+F:	include/uapi/linux/qemu_fw_cfg.h
 
 QIB DRIVER
 M:	Dennis Dalessandro <dennis.dalessandro@intel.com>

drivers/firmware/qemu_fw_cfg.c

@@ -32,30 +32,12 @@
 #include <linux/slab.h>
 #include <linux/io.h>
 #include <linux/ioport.h>
+#include <uapi/linux/qemu_fw_cfg.h>
 
 MODULE_AUTHOR("Gabriel L. Somlo <somlo@cmu.edu>");
 MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
 MODULE_LICENSE("GPL");
 
-/* selector key values for "well-known" fw_cfg entries */
-#define FW_CFG_SIGNATURE  0x00
-#define FW_CFG_ID         0x01
-#define FW_CFG_FILE_DIR   0x19
-
-/* size in bytes of fw_cfg signature */
-#define FW_CFG_SIG_SIZE 4
-
-/* fw_cfg "file name" is up to 56 characters (including terminating nul) */
-#define FW_CFG_MAX_FILE_PATH 56
-
-/* fw_cfg file directory entry type */
-struct fw_cfg_file {
-	u32 size;
-	u16 select;
-	u16 reserved;
-	char name[FW_CFG_MAX_FILE_PATH];
-};
-
 /* fw_cfg device i/o register addresses */
 static bool fw_cfg_is_mmio;
 static phys_addr_t fw_cfg_p_base;
@@ -616,7 +598,7 @@ MODULE_DEVICE_TABLE(of, fw_cfg_sysfs_mmio_match);
 
 #ifdef CONFIG_ACPI
 static const struct acpi_device_id fw_cfg_sysfs_acpi_match[] = {
-	{ "QEMU0002", },
+	{ FW_CFG_ACPI_DEVICE_ID, },
 	{},
 };
 MODULE_DEVICE_TABLE(acpi, fw_cfg_sysfs_acpi_match);

include/uapi/linux/qemu_fw_cfg.h

@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: BSD-3-Clause */
+#ifndef _LINUX_FW_CFG_H
+#define _LINUX_FW_CFG_H
+
+#include <linux/types.h>
+
+#define FW_CFG_ACPI_DEVICE_ID	"QEMU0002"
+
+/* selector key values for "well-known" fw_cfg entries */
+#define FW_CFG_SIGNATURE	0x00
+#define FW_CFG_ID		0x01
+#define FW_CFG_UUID		0x02
+#define FW_CFG_RAM_SIZE		0x03
+#define FW_CFG_NOGRAPHIC	0x04
+#define FW_CFG_NB_CPUS		0x05
+#define FW_CFG_MACHINE_ID	0x06
+#define FW_CFG_KERNEL_ADDR	0x07
+#define FW_CFG_KERNEL_SIZE	0x08
+#define FW_CFG_KERNEL_CMDLINE	0x09
+#define FW_CFG_INITRD_ADDR	0x0a
+#define FW_CFG_INITRD_SIZE	0x0b
+#define FW_CFG_BOOT_DEVICE	0x0c
+#define FW_CFG_NUMA		0x0d
+#define FW_CFG_BOOT_MENU	0x0e
+#define FW_CFG_MAX_CPUS		0x0f
+#define FW_CFG_KERNEL_ENTRY	0x10
+#define FW_CFG_KERNEL_DATA	0x11
+#define FW_CFG_INITRD_DATA	0x12
+#define FW_CFG_CMDLINE_ADDR	0x13
+#define FW_CFG_CMDLINE_SIZE	0x14
+#define FW_CFG_CMDLINE_DATA	0x15
+#define FW_CFG_SETUP_ADDR	0x16
+#define FW_CFG_SETUP_SIZE	0x17
+#define FW_CFG_SETUP_DATA	0x18
+#define FW_CFG_FILE_DIR		0x19
+
+#define FW_CFG_FILE_FIRST	0x20
+#define FW_CFG_FILE_SLOTS_MIN	0x10
+
+#define FW_CFG_WRITE_CHANNEL	0x4000
+#define FW_CFG_ARCH_LOCAL	0x8000
+#define FW_CFG_ENTRY_MASK	(~(FW_CFG_WRITE_CHANNEL | FW_CFG_ARCH_LOCAL))
+
+#define FW_CFG_INVALID		0xffff
+
+/* width in bytes of fw_cfg control register */
+#define FW_CFG_CTL_SIZE		0x02
+
+/* fw_cfg "file name" is up to 56 characters (including terminating nul) */
+#define FW_CFG_MAX_FILE_PATH	56
+
+/* size in bytes of fw_cfg signature */
+#define FW_CFG_SIG_SIZE 4
+
+/* FW_CFG_ID bits */
+#define FW_CFG_VERSION		0x01
+
+/* fw_cfg file directory entry type */
+struct fw_cfg_file {
+	__be32 size;
+	__be16 select;
+	__u16 reserved;
+	char name[FW_CFG_MAX_FILE_PATH];
+};
+
+#endif