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From:   Emil Renner Berthing <emil.renner.berthing@canonical.com>
In-Reply-To: <20230911-optimize_checksum-v4-1-77cc2ad9e9d7@rivosinc.com>
References: <20230911-optimize_checksum-v4-0-77cc2ad9e9d7@rivosinc.com> <20230911-optimize_checksum-v4-1-77cc2ad9e9d7@rivosinc.com>
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Date:   Tue, 12 Sep 2023 03:24:29 -0700
Message-ID: <CAJM55Z-kj8eWKvR32At4kx+PPPn9OMaR88BhEqppQHSL03n50Q@mail.gmail.com>
Subject: Re: [PATCH v4 1/5] riscv: Checksum header
To:     Charlie Jenkins <charlie@rivosinc.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Conor Dooley <conor@kernel.org>,
        Samuel Holland <samuel.holland@sifive.com>,
        David Laight <David.Laight@aculab.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>
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Precedence: bulk

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@rivosinc.com>
> ---
>  arch/riscv/include/asm/checksum.h | 95 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 95 insertions(+)
>
> diff --git a/arch/riscv/include/asm/checksum.h b/arch/riscv/include/asm/checksum.h
> new file mode 100644
> index 000000000000..0d7fc8275a5e
> --- /dev/null
> +++ b/arch/riscv/include/asm/checksum.h
> @@ -0,0 +1,95 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * IP 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>
> +
> +#ifdef CONFIG_32BIT
> +typedef unsigned int csum_t;
> +#else
> +typedef unsigned long csum_t;
> +#endif

Hi Charlie,

Isn't unsigned long already 32bit on 32bit RISC-V, so why is this #ifdef
needed?

> +
> +/*
> + *	Fold a partial checksum without adding pseudo headers
> + */
> +static inline __sum16 csum_fold(__wsum sum)
> +{
> +	return (~sum - ror32(sum, 16)) >> 16;
> +}
> +
> +#define csum_fold csum_fold
> +
> +/*
> + * 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.
> + */
> +static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
> +{
> +	csum_t 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)) {
> +		csum_t 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 csum >> 16;
> +	}
> +no_zbb:
> +#ifndef CONFIG_32BIT
> +		csum += (csum >> 32) | (csum << 32);
> +		csum >>= 32;

The indentation seems off here.

/Emil

> +#endif
> +	return csum_fold((__force __wsum)csum);
> +}
> +
> +#define ip_fast_csum ip_fast_csum
> +
> +#include <asm-generic/checksum.h>
> +
> +#endif // __ASM_RISCV_CHECKSUM_H
>
> --
> 2.42.0
>
>
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