On Tue, Oct 31, 2023 at 05:18:53PM -0700, Charlie Jenkins wrote:
> 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>
> ---
> arch/riscv/include/asm/checksum.h | 81 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 81 insertions(+)
>
> diff --git a/arch/riscv/include/asm/checksum.h b/arch/riscv/include/asm/checksum.h
> new file mode 100644
> index 000000000000..3d77cac338fe
> --- /dev/null
> +++ b/arch/riscv/include/asm/checksum.h
> @@ -0,0 +1,81 @@
> +/* 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 is the number of 32 bit segments and must be greater than or equal to 5.
> + * @iph is 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)
This looks like a open coding of riscv_has_extension_*, so if
we use the it, the code could be rewritten as:
if (riscv_has_extension_likely(RISCV_ISA_EXT_ZBB)) {
if (32bit) {
asm(...)
} else {
asm(...)
}
return csum >> 16;
}
#ifndef CONFIG_32BIT
csum += ror64(csum, 32);
csum >>= 32;
#endif
return csum_fold((__force __wsum)csum);
The code readability is improved and make it a bit easier to refactor
the asm(...) code in the future.
And IMHO, the generated code should be the same.
Thanks
>
> + :
> + :
> + :
> + : 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 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 */
>
> --
> 2.34.1
>
>
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