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Date:   Tue, 12 Sep 2023 19:38:03 -0700
From:   Charlie Jenkins <charlie@rivosinc.com>
To:     Emil Renner Berthing <emil.renner.berthing@canonical.com>
Cc:     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,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>
Subject: Re: [PATCH v4 1/5] riscv: Checksum header
Message-ID: <ZQEgi9v1gt6MlkDv@ghost>
References: <20230911-optimize_checksum-v4-0-77cc2ad9e9d7@rivosinc.com>
 <20230911-optimize_checksum-v4-1-77cc2ad9e9d7@rivosinc.com>
 <CAJM55Z-kj8eWKvR32At4kx+PPPn9OMaR88BhEqppQHSL03n50Q@mail.gmail.com>
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On Tue, Sep 12, 2023 at 03:24:29AM -0700, Emil Renner Berthing wrote:
> 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?
Oh, I wasn't sure so I ran sizeof(long) in qemu-system-riscv32 and it
gave me 8 so assumed a long was 8 bytes. Do you think it would make what
is going on more clear if I use u32 and u64 or would you recommend just
using long?
> 
> > +
> > +/*
> > + *	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
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.inradead.org/mailman/listinfo/linux-riscv