[FFmpeg-devel] [PATCH 2/2] lavc/videodsp: RISC-V zicbop prefetch

[Rémi Denis-Courmont]

There are currently no ways to run-time detect the CPU capability, so we
take it for granted (in the worst case, it will execute NOPs).
---
 libavcodec/riscv/Makefile        |  2 ++
 libavcodec/riscv/videodsp.S      | 34 ++++++++++++++++++++++++++++++
 libavcodec/riscv/videodsp_init.c | 36 ++++++++++++++++++++++++++++++++
 libavcodec/videodsp.c            |  2 ++
 libavcodec/videodsp.h            |  1 +
 5 files changed, 75 insertions(+)
 create mode 100644 libavcodec/riscv/videodsp.S
 create mode 100644 libavcodec/riscv/videodsp_init.c

diff --git a/libavcodec/riscv/Makefile b/libavcodec/riscv/Makefile
index 0bbdd38116..05d0646256 100644
--- a/libavcodec/riscv/Makefile
+++ b/libavcodec/riscv/Makefile
@@ -67,6 +67,8 @@ RVV-OBJS-$(CONFIG_UTVIDEO_DECODER) += riscv/utvideodsp_rvv.o
 OBJS-$(CONFIG_VC1DSP) += riscv/vc1dsp_init.o
 RV-OBJS-$(CONFIG_VC1DSP) += riscv/vc1dsp_rvi.o
 RVV-OBJS-$(CONFIG_VC1DSP) += riscv/vc1dsp_rvv.o
+OBJS-$(CONFIG_VIDEODSP) += riscv/videodsp_init.o
+RV-OBJS-$(CONFIG_VIDEODSP) += riscv/videodsp.o
 OBJS-$(CONFIG_VP7_DECODER) += riscv/vp7dsp_init.o
 RVV-OBJS-$(CONFIG_VP7_DECODER) += riscv/vp7dsp_rvv.o
 OBJS-$(CONFIG_VP8DSP) += riscv/vp8dsp_init.o
diff --git a/libavcodec/riscv/videodsp.S b/libavcodec/riscv/videodsp.S
new file mode 100644
index 0000000000..72bf70ec52
--- /dev/null
+++ b/libavcodec/riscv/videodsp.S
@@ -0,0 +1,34 @@
+/*
+ * Copyright © 2022 Rémi Denis-Courmont.
+ *
+ * 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 "config.h"
+#include "libavutil/riscv/asm.S"
+
+#if HAVE_RV_ZICBOP
+func ff_prefetch_rv_zicbop, zicbop
+1:
+        addi    a2, a2, -1
+        prefetch.r  (a0)
+        add     a0, a0, a1
+        bnez    a2, 1b
+
+        ret
+endfunc
+#endif
diff --git a/libavcodec/riscv/videodsp_init.c b/libavcodec/riscv/videodsp_init.c
new file mode 100644
index 0000000000..f2c9aae3ca
--- /dev/null
+++ b/libavcodec/riscv/videodsp_init.c
@@ -0,0 +1,36 @@
+/*
+ * 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 "config.h"
+#include "libavutil/attributes.h"
+#include "libavutil/cpu.h"
+#include "libavcodec/videodsp.h"
+
+void ff_prefetch_rv_zicbop(const uint8_t *mem, ptrdiff_t stride, int h);
+
+av_cold void ff_videodsp_init_riscv(VideoDSPContext *ctx, int bpc)
+{
+#if HAVE_RV_ZICBOP
+    /* TODO: Since we pay for the indirect function call anyway, we should
+     * only set this if Cache-Block Operation Prefetch (Zicbop) is actually
+     * supported and otherwise save a few cycles of NOPs.
+     * But so far there are no means to detect Zicbop (in user mode).
+     */
+    ctx->prefetch = ff_prefetch_rv_zicbop;
+#endif
+}
diff --git a/libavcodec/videodsp.c b/libavcodec/videodsp.c
index bdff2e76f5..a19e87a819 100644
--- a/libavcodec/videodsp.c
+++ b/libavcodec/videodsp.c
@@ -51,6 +51,8 @@ av_cold void ff_videodsp_init(VideoDSPContext *ctx, int bpc)
     ff_videodsp_init_arm(ctx, bpc);
 #elif ARCH_PPC
     ff_videodsp_init_ppc(ctx, bpc);
+#elif ARCH_RISCV
+    ff_videodsp_init_riscv(ctx, bpc);
 #elif ARCH_X86
     ff_videodsp_init_x86(ctx, bpc);
 #elif ARCH_MIPS
diff --git a/libavcodec/videodsp.h b/libavcodec/videodsp.h
index e8960b609d..1be3188d09 100644
--- a/libavcodec/videodsp.h
+++ b/libavcodec/videodsp.h
@@ -81,6 +81,7 @@ void ff_videodsp_init(VideoDSPContext *ctx, int bpc);
 void ff_videodsp_init_aarch64(VideoDSPContext *ctx, int bpc);
 void ff_videodsp_init_arm(VideoDSPContext *ctx, int bpc);
 void ff_videodsp_init_ppc(VideoDSPContext *ctx, int bpc);
+void ff_videodsp_init_riscv(VideoDSPContext *ctx, int bpc);
 void ff_videodsp_init_x86(VideoDSPContext *ctx, int bpc);
 void ff_videodsp_init_mips(VideoDSPContext *ctx, int bpc);
 void ff_videodsp_init_loongarch(VideoDSPContext *ctx, int bpc);
-- 
2.45.2