linux-kernel - Re: [PATCH v4 1/5] riscv: Checksum header

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Message-ID: <CAJM55Z9SC0ET=tBJ7s0pz+L4tRSC02yogsWtmsuhr=-jf04yjQ@mail.gmail.com>
Date:   Wed, 13 Sep 2023 02:19:43 -0700
From:   Emil Renner Berthing <emil.renner.berthing@...onical.com>
To:     Charlie Jenkins <charlie@...osinc.com>,
        Emil Renner Berthing <emil.renner.berthing@...onical.com>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Conor Dooley <conor@...nel.org>,
        Samuel Holland <samuel.holland@...ive.com>,
        David Laight <David.Laight@...lab.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>
Subject: Re: [PATCH v4 1/5] riscv: Checksum header

Charlie Jenkins wrote:
> 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@...osinc.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?

Yeah, it doesn't seem like csum_t is used anywhere else, so I'd just use
unsigned long if all you want is a register sized unsigned value. It'll be more
familiar and easier to read for most people.

> >
> > > +
> > > +/*
> > > + *	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@...ts.infradead.org
> > > http://lists.inradead.org/mailman/listinfo/linux-riscv

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