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Message-ID: <DM8PR11MB57517DB5180352D536565A4FB8A9A@DM8PR11MB5751.namprd11.prod.outlook.com>
Date: Tue, 7 Nov 2023 07:33:19 +0000
From: "Wang, Xiao W" <xiao.w.wang@...el.com>
To: Charlie Jenkins <charlie@...osinc.com>,
Palmer Dabbelt <palmer@...belt.com>,
Conor Dooley <conor@...nel.org>,
Samuel Holland <samuel.holland@...ive.com>,
David Laight <David.Laight@...lab.com>,
"Evan Green" <evan@...osinc.com>,
"linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
CC: Paul Walmsley <paul.walmsley@...ive.com>,
Albert Ou <aou@...s.berkeley.edu>,
Arnd Bergmann <arnd@...db.de>,
Conor Dooley <conor.dooley@...rochip.com>
Subject: RE: [PATCH v10 3/5] riscv: Checksum header
> -----Original Message-----
> From: Charlie Jenkins <charlie@...osinc.com>
> Sent: Thursday, November 2, 2023 6:48 AM
> To: Charlie Jenkins <charlie@...osinc.com>; Palmer Dabbelt
> <palmer@...belt.com>; Conor Dooley <conor@...nel.org>; Samuel Holland
> <samuel.holland@...ive.com>; David Laight <David.Laight@...lab.com>;
> Wang, Xiao W <xiao.w.wang@...el.com>; Evan Green <evan@...osinc.com>;
> linux-riscv@...ts.infradead.org; linux-kernel@...r.kernel.org; linux-
> arch@...r.kernel.org
> Cc: Paul Walmsley <paul.walmsley@...ive.com>; Albert Ou
> <aou@...s.berkeley.edu>; Arnd Bergmann <arnd@...db.de>; Conor Dooley
> <conor.dooley@...rochip.com>
> Subject: [PATCH v10 3/5] riscv: Checksum header
Is it better to make the title more descriptive as "riscv: Add checksum header"?
>
> 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@...osinc.com>
> Acked-by: Conor Dooley <conor.dooley@...rochip.com>
> ---
> 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.
> + */
For comments on API parameters, it's better to follow the "@para: xxx" standard format
and indention alignment used in other places.
> +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 csum >> 16;
> + }
> +no_zbb:
> +#ifndef CONFIG_32BIT
> + csum += ror64(csum, 32);
> + csum >>= 32;
> +#endif
> + return csum_fold((__force __wsum)csum);
> +}
The algorithm looks good to me.
BRs,
Xiao
> +
> +#endif /* __ASM_RISCV_CHECKSUM_H */
>
> --
> 2.34.1
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