support framework for RunTime Cpu Detection

Just add related code about RTCD to setup the framework.
Have not support the actual runtime detection, and I have
not understood how RTCD works, FIXME. More analysis please
refer to https://github.com/aosp-riscv/libvpx/issues/8#issuecomment-1627896402.

Signed-off-by: Wang Chen <wangchen20@iscas.ac.cn>
Co-authored-by: sun min <sunmin89@outlook.com>

4 files changed, 116 insertions, 0 deletions

diff --git a/build/make/rtcd.pl b/build/make/rtcd.pl
index f4edeaad5..b7555ad7c 100755
--- a/build/make/rtcd.pl
+++ b/build/make/rtcd.pl
@@ -418,6 +418,37 @@ EOF
   common_bottom;
 }
 
+sub riscv() {
+  determine_indirection("c", @ALL_ARCHS);
+
+  # Assign the helper variable for each enabled extension
+  foreach my $opt (@ALL_ARCHS) {
+    my $opt_uc = uc $opt;
+    eval "\$have_${opt}=\"flags & HAS_${opt_uc}\"";
+  }
+
+  common_top;
+  print <<EOF;
+#include "vpx_config.h"
+
+#ifdef RTCD_C
+#include "vpx_ports/riscv.h"
+static void setup_rtcd_internal(void)
+{
+    int flags = riscv_cpu_caps();
+
+    (void)flags;
+EOF
+
+  set_function_pointers("c", @ALL_ARCHS);
+
+  print <<EOF;
+}
+#endif
+EOF
+  common_bottom;
+}
+
 sub unoptimized() {
   determine_indirection "c";
   common_top;
@@ -497,6 +528,9 @@ if ($opts{arch} eq 'x86') {
 } elsif ($opts{arch} =~ /loongarch/ ) {
   @ALL_ARCHS = filter(qw/lsx lasx/);
   loongarch;
+} elsif ($opts{arch} =~ /riscv/ ) {
+  @ALL_ARCHS = filter(qw/rvv/);
+  riscv;
 } else {
   unoptimized;
 }
diff --git a/vpx_ports/riscv.h b/vpx_ports/riscv.h
new file mode 100644
index 000000000..7feb763d5
--- /dev/null
+++ b/vpx_ports/riscv.h
@@ -0,0 +1,26 @@
+/*
+ *  Copyright (c) 2023 The WebM project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef VPX_VPX_PORTS_RISCV_H_
+#define VPX_VPX_PORTS_RISCV_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define HAS_RVV 0x01
+
+int riscv_cpu_caps(void);
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // VPX_VPX_PORTS_RISCV_H_
\ No newline at end of file
diff --git a/vpx_ports/riscv_cpudetect.c b/vpx_ports/riscv_cpudetect.c
new file mode 100644
index 000000000..830b18869
--- /dev/null
+++ b/vpx_ports/riscv_cpudetect.c
@@ -0,0 +1,53 @@
+/*
+ *  Copyright (c) 2017 The WebM project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdint.h>
+
+#include "./vpx_config.h"
+#include "vpx_ports/riscv.h"
+
+#if CONFIG_RUNTIME_CPU_DETECT
+static int cpu_env_flags(int *flags) {
+  char *env;
+  env = getenv("VPX_SIMD_CAPS");
+  if (env && *env) {
+    *flags = (int)strtol(env, NULL, 0);
+    return 0;
+  }
+  *flags = 0;
+  return -1;
+}
+
+static int cpu_env_mask(void) {
+  char *env;
+  env = getenv("VPX_SIMD_CAPS_MASK");
+  return env && *env ? (int)strtol(env, NULL, 0) : ~0;
+}
+
+int riscv_cpu_caps(void) {
+  int flags = HAS_RVV;
+  int mask;
+
+  // If VPX_SIMD_CAPS is set then allow only those capabilities.
+  if (!cpu_env_flags(&flags)) {
+    return flags;
+  }
+
+  mask = cpu_env_mask();
+
+  return flags & mask;
+}
+#else
+// If there is no RTCD the function pointers are not used and can not be
+// changed.
+int riscv_cpu_caps(void) { return 0; }
+#endif  // CONFIG_RUNTIME_CPU_DETECT
diff --git a/vpx_ports/vpx_ports.mk b/vpx_ports/vpx_ports.mk
index e30e87cef..8c57ab4ce 100644
--- a/vpx_ports/vpx_ports.mk
+++ b/vpx_ports/vpx_ports.mk
@@ -48,6 +48,9 @@ PORTS_SRCS-$(VPX_ARCH_MIPS) += mips.h
 PORTS_SRCS-$(VPX_ARCH_LOONGARCH) += loongarch_cpudetect.c
 PORTS_SRCS-$(VPX_ARCH_LOONGARCH) += loongarch.h
 
+PORTS_SRCS-$(VPX_ARCH_RISCV64) += riscv_cpudetect.c
+PORTS_SRCS-$(VPX_ARCH_RISCV64) += riscv.h
+
 ifeq ($(VPX_ARCH_MIPS), yes)
 PORTS_SRCS-yes += asmdefs_mmi.h
 endif