[FFmpeg-devel] [PATCH 01/12] lavu/riscv: add CPU flags for the RISC-V Vector extension

[remi@remlab.net]

From: Rémi Denis-Courmont <remi@remlab.net>

RVV defines a total of 12 different extensions, including:

- 5 different instruction subsets:
  - Zve32x: 8-, 16- and 32-bit integers,
  - Zve32f: Zve32x plus single precision floats,
  - Zve64x: Zve32x plus 64-bit integers,
  - Zve64f: Zve32f plus Zve64x,
  - Zve64d: Zve64f plus double precision floats.

- 6 different vector lengths:
  - Zvl32b (embedded only),
  - Zvl64b (embedded only),
  - Zvl128b,
  - Zvl256b,
  - Zvl512b,
  - Zvl1024b,

- and the V extension proper: equivalent to Zve64f and Zvl128b.

In total, there are 6 different possible sets of supported instructions
(including the empty set), but for convenience we allocate one bit for
each type sets: up-to-32-bit ints (ZVE32X), floats (ZV32F),
64-bit ints (ZV64X) and doubles (ZVE64D).

Whence the vector size is needed, it can be retrieved by reading the
unprivileged read-only vlenb CSR. This should probably be a separate
helper macro if needed at a later point.
---
 libavutil/cpu.c          | 15 +++++++++++
 libavutil/cpu.h          |  6 +++++
 libavutil/cpu_internal.h |  1 +
 libavutil/riscv/Makefile |  1 +
 libavutil/riscv/cpu.c    | 57 ++++++++++++++++++++++++++++++++++++++++
 5 files changed, 80 insertions(+)
 create mode 100644 libavutil/riscv/Makefile
 create mode 100644 libavutil/riscv/cpu.c

diff --git a/libavutil/cpu.c b/libavutil/cpu.c
index 0035e927a5..89d2fb6f56 100644
--- a/libavutil/cpu.c
+++ b/libavutil/cpu.c
@@ -62,6 +62,8 @@ static int get_cpu_flags(void)
     return ff_get_cpu_flags_arm();
 #elif ARCH_PPC
     return ff_get_cpu_flags_ppc();
+#elif ARCH_RISCV
+    return ff_get_cpu_flags_riscv();
 #elif ARCH_X86
     return ff_get_cpu_flags_x86();
 #elif ARCH_LOONGARCH
@@ -178,6 +180,19 @@ int av_parse_cpu_caps(unsigned *flags, const char *s)
 #elif ARCH_LOONGARCH
         { "lsx",      NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_LSX      },    .unit = "flags" },
         { "lasx",     NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_LASX     },    .unit = "flags" },
+#elif ARCH_RISCV
+#define AV_CPU_FLAG_ZVE32X_M (AV_CPU_FLAG_ZVE32X)
+#define AV_CPU_FLAG_ZVE32F_M (AV_CPU_FLAG_ZVE32X_M | AV_CPU_FLAG_ZVE32F)
+#define AV_CPU_FLAG_ZVE64X_M (AV_CPU_FLAG_ZVE32X_M | AV_CPU_FLAG_ZVE64X)
+#define AV_CPU_FLAG_ZVE64F_M (AV_CPU_FLAG_ZVE32F_M | AV_CPU_FLAG_ZVE64X)
+#define AV_CPU_FLAG_ZVE64D_M (AV_CPU_FLAG_ZVE64F_M | AV_CPU_FLAG_ZVE64D)
+#define AV_CPU_FLAG_VECTORS  AV_CPU_FLAG_ZVE64D_M
+        { "vectors",  NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_VECTORS  },    .unit = "flags" },
+        { "zve32x",   NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_ZVE32X   },    .unit = "flags" },
+        { "zve32f",   NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_ZVE32F_M },    .unit = "flags" },
+        { "zve64x",   NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_ZVE64X_M },    .unit = "flags" },
+        { "zve64f",   NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_ZVE64F_M },    .unit = "flags" },
+        { "zve64d",   NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_ZVE64D_M },    .unit = "flags" },
 #endif
         { NULL },
     };
diff --git a/libavutil/cpu.h b/libavutil/cpu.h
index 9711e574c5..44836e50d6 100644
--- a/libavutil/cpu.h
+++ b/libavutil/cpu.h
@@ -78,6 +78,12 @@
 #define AV_CPU_FLAG_LSX          (1 << 0)
 #define AV_CPU_FLAG_LASX         (1 << 1)
 
+// RISC-V Vector extension
+#define AV_CPU_FLAG_ZVE32X       (1 << 0) /* 8-, 16-, 32-bit integers */
+#define AV_CPU_FLAG_ZVE32F       (1 << 1) /* single precision scalars */
+#define AV_CPU_FLAG_ZVE64X       (1 << 2) /* 64-bit integers */
+#define AV_CPU_FLAG_ZVE64D       (1 << 3) /* double precision scalars */
+
 /**
  * Return the flags which specify extensions supported by the CPU.
  * The returned value is affected by av_force_cpu_flags() if that was used
diff --git a/libavutil/cpu_internal.h b/libavutil/cpu_internal.h
index 650d47fc96..634f28bac4 100644
--- a/libavutil/cpu_internal.h
+++ b/libavutil/cpu_internal.h
@@ -48,6 +48,7 @@ int ff_get_cpu_flags_mips(void);
 int ff_get_cpu_flags_aarch64(void);
 int ff_get_cpu_flags_arm(void);
 int ff_get_cpu_flags_ppc(void);
+int ff_get_cpu_flags_riscv(void);
 int ff_get_cpu_flags_x86(void);
 int ff_get_cpu_flags_loongarch(void);
 
diff --git a/libavutil/riscv/Makefile b/libavutil/riscv/Makefile
new file mode 100644
index 0000000000..1f818043dc
--- /dev/null
+++ b/libavutil/riscv/Makefile
@@ -0,0 +1 @@
+OBJS += riscv/cpu.o
diff --git a/libavutil/riscv/cpu.c b/libavutil/riscv/cpu.c
new file mode 100644
index 0000000000..9e4cce5e8b
--- /dev/null
+++ b/libavutil/riscv/cpu.c
@@ -0,0 +1,57 @@
+/*
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "libavutil/cpu.h"
+#include "libavutil/cpu_internal.h"
+#include "config.h"
+
+#if HAVE_GETAUXVAL
+#include <sys/auxv.h>
+#endif
+
+#define HWCAP_RV(letter) (1ul << ((letter) - 'A'))
+
+int ff_get_cpu_flags_riscv(void)
+{
+    int ret = 0;
+
+    /* If RV-V is enabled statically at compile-time, check the details. */
+#ifdef __riscv_vectors
+    ret |= AV_CPU_FLAG_ZVE32X;
+#if __riscv_v_elen >= 64
+    ret |= AV_CPU_FLAG_ZVE64X;
+#endif
+#if __riscv_v_elen_fp >= 32
+    ret |= AV_CPU_FLAG_ZVE32F;
+#if __riscv_v_elen_fp >= 64
+    ret |= AV_CPU_FLAG_ZVE64F;
+#endif
+#endif
+#endif
+
+#if HAVE_GETAUXVAL
+    const unsigned long hwcap = getauxval(AT_HWCAP);
+
+    /* The V extension implies all subsets */
+    if (hwcap & HWCAP_RV('V'))
+        ret |= AV_CPU_FLAG_ZVE32X | AV_CPU_FLAG_ZVE64X
+             | AV_CPU_FLAG_ZVE32F | AV_CPU_FLAG_ZVE64D;
+#endif
+
+    return ret;
+}
-- 
2.37.2

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