Provide checksum algorithms that have been designed to leverage riscv
instructions such as rotate. In 64-bit, can take advantage of the larger
register to avoid some overflow checking.
Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
Acked-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
Reviewed-by: Xiao Wang <xiao.w.wang@xxxxxxxxx>
---
arch/riscv/include/asm/checksum.h | 82 +++++++++++++++++++++++++++++++++++++++
1 file changed, 82 insertions(+)
diff --git a/arch/riscv/include/asm/checksum.h b/arch/riscv/include/asm/checksum.h
new file mode 100644
index 000000000000..5a810126aac7
--- /dev/null
+++ b/arch/riscv/include/asm/checksum.h
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Checksum routines
+ *
+ * Copyright (C) 2023 Rivos Inc.
+ */
+#ifndef __ASM_RISCV_CHECKSUM_H
+#define __ASM_RISCV_CHECKSUM_H
+
+#include <linux/in6.h>
+#include <linux/uaccess.h>
+
+#define ip_fast_csum ip_fast_csum
+
+/* Define riscv versions of functions before importing asm-generic/checksum.h */
+#include <asm-generic/checksum.h>
+
+/**
+ * Quickly compute an IP checksum with the assumption that IPv4 headers will
+ * always be in multiples of 32-bits, and have an ihl of at least 5.
+ *
+ * @ihl: the number of 32 bit segments and must be greater than or equal to 5.
+ * @iph: assumed to be word aligned given that NET_IP_ALIGN is set to 2 on
+ * riscv, defining IP headers to be aligned.
+ */
+static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
+{
+ unsigned long csum = 0;
+ int pos = 0;
+
+ do {
+ csum += ((const unsigned int *)iph)[pos];
+ if (IS_ENABLED(CONFIG_32BIT))
+ csum += csum < ((const unsigned int *)iph)[pos];
+ } while (++pos < ihl);
+
+ /*
+ * ZBB only saves three instructions on 32-bit and five on 64-bit so not
+ * worth checking if supported without Alternatives.
+ */
+ if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
+ IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
+ unsigned long fold_temp;
+
+ asm_volatile_goto(ALTERNATIVE("j %l[no_zbb]", "nop", 0,
+ RISCV_ISA_EXT_ZBB, 1)
+ :
+ :
+ :
+ : no_zbb);
+
+ if (IS_ENABLED(CONFIG_32BIT)) {
+ asm(".option push \n\
+ .option arch,+zbb \n\
+ not %[fold_temp], %[csum] \n\
+ rori %[csum], %[csum], 16 \n\
+ sub %[csum], %[fold_temp], %[csum] \n\
+ .option pop"
+ : [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp));
+ } else {
+ asm(".option push \n\
+ .option arch,+zbb \n\
+ rori %[fold_temp], %[csum], 32 \n\
+ add %[csum], %[fold_temp], %[csum] \n\
+ srli %[csum], %[csum], 32 \n\
+ not %[fold_temp], %[csum] \n\
+ roriw %[csum], %[csum], 16 \n\
+ subw %[csum], %[fold_temp], %[csum] \n\
+ .option pop"
+ : [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp));
+ }
+ return (__force __sum16)(csum >> 16);
+ }
+no_zbb:
+#ifndef CONFIG_32BIT
+ csum += ror64(csum, 32);
+ csum >>= 32;
+#endif
+ return csum_fold((__force __wsum)csum);
+}
+
+#endif /* __ASM_RISCV_CHECKSUM_H */
--
2.43.0
