efi: add helper function to get UEFI params from FDT

ARM and ARM64 architectures use the device tree to pass UEFI parameters
from stub to kernel. These parameters are things known to the stub but
not discoverable by the kernel after the stub calls ExitBootSerives().
There is a helper function in:

   drivers/firmware/efi/fdt.c

which the stub uses to add the UEFI parameters to the device tree.
This patch adds a complimentary helper function which UEFI runtime
support may use to retrieve the parameters from the device tree.
If an architecture wants to use this helper, it should select
CONFIG_EFI_PARAMS_FROM_FDT.

Signed-off-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

2 files changed, 86 insertions, 0 deletions

diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index 1e75f48b61f8..d420ae2d3413 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -47,6 +47,13 @@ config EFI_RUNTIME_MAP
 
           See also Documentation/ABI/testing/sysfs-firmware-efi-runtime-map.
 
+config EFI_PARAMS_FROM_FDT
+        bool
+        help
+          Select this config option from the architecture Kconfig if
+          the EFI runtime support gets system table address, memory
+          map address, and other parameters from the device tree.
+
 endmenu
 
 config UEFI_CPER
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index af20f1712337..cd36deb619fa 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -20,6 +20,8 @@
 #include <linux/init.h>
 #include <linux/device.h>
 #include <linux/efi.h>
+#include <linux/of.h>
+#include <linux/of_fdt.h>
 #include <linux/io.h>
 
 struct efi __read_mostly efi = {
@@ -318,3 +320,80 @@ int __init efi_config_init(efi_config_table_type_t *arch_tables)
 
         return 0;
 }
+
+#ifdef CONFIG_EFI_PARAMS_FROM_FDT
+
+#define UEFI_PARAM(name, prop, field)                      \
+        {                                                  \
+                { name },                                  \
+                { prop },                                  \
+                offsetof(struct efi_fdt_params, field),    \
+                FIELD_SIZEOF(struct efi_fdt_params, field) \
+        }
+
+static __initdata struct {
+        const char name[32];
+        const char propname[32];
+        int offset;
+        int size;
+} dt_params[] = {
+        UEFI_PARAM("System Table", "linux,uefi-system-table", system_table),
+        UEFI_PARAM("MemMap Address", "linux,uefi-mmap-start", mmap),
+        UEFI_PARAM("MemMap Size", "linux,uefi-mmap-size", mmap_size),
+        UEFI_PARAM("MemMap Desc. Size", "linux,uefi-mmap-desc-size", desc_size),
+        UEFI_PARAM("MemMap Desc. Version", "linux,uefi-mmap-desc-ver", desc_ver)
+};
+
+struct param_info {
+        int verbose;
+        void *params;
+};
+
+static int __init fdt_find_uefi_params(unsigned long node, const char *uname,
+                                       int depth, void *data)
+{
+        struct param_info *info = data;
+        void *prop, *dest;
+        unsigned long len;
+        u64 val;
+        int i;
+
+        if (depth != 1 ||
+            (strcmp(uname, "chosen") != 0 && strcmp(uname, "chosen@0") != 0))
+                return 0;
+
+        pr_info("Getting parameters from FDT:\n");
+
+        for (i = 0; i < ARRAY_SIZE(dt_params); i++) {
+                prop = of_get_flat_dt_prop(node, dt_params[i].propname, &len);
+                if (!prop) {
+                        pr_err("Can't find %s in device tree!\n",
+                               dt_params[i].name);
+                        return 0;
+                }
+                dest = info->params + dt_params[i].offset;
+
+                val = of_read_number(prop, len / sizeof(u32));
+
+                if (dt_params[i].size == sizeof(u32))
+                        *(u32 *)dest = val;
+                else
+                        *(u64 *)dest = val;
+
+                if (info->verbose)
+                        pr_info("  %s: 0x%0*llx\n", dt_params[i].name,
+                                dt_params[i].size * 2, val);
+        }
+        return 1;
+}
+
+int __init efi_get_fdt_params(struct efi_fdt_params *params, int verbose)
+{
+        struct param_info info;
+
+        info.verbose = verbose;
+        info.params = params;
+
+        return of_scan_flat_dt(fdt_find_uefi_params, &info);
+}
+#endif /* CONFIG_EFI_PARAMS_FROM_FDT */