linux-kernel - Re: [PATCH v3 1/4] x86/boot: Add acpitb.h to help parse acpi tables

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Date:   Thu, 19 Jul 2018 17:19:43 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
cc:     linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
        mingo@...hat.com, bhe@...hat.com, keescook@...omium.org,
        yasu.isimatu@...il.com, indou.takao@...fujitsu.com,
        lcapitulino@...hat.com, caoj.fnst@...fujitsu.com,
        douly.fnst@...fujitsu.com
Subject: Re: [PATCH v3 1/4] x86/boot: Add acpitb.h to help parse acpi
 tables

On Tue, 17 Jul 2018, Chao Fan wrote:

> In order to parse ACPI tables, reuse the head file linux/acpi.h,
> so that the files in 'compressed' directory can read ACPI table
> by including this head file.
> 
> Signed-off-by: Chao Fan <fanc.fnst@...fujitsu.com>
> ---
>  arch/x86/boot/compressed/acpitb.h | 50 +++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
>  create mode 100644 arch/x86/boot/compressed/acpitb.h
> 
> diff --git a/arch/x86/boot/compressed/acpitb.h b/arch/x86/boot/compressed/acpitb.h
> new file mode 100644
> index 000000000000..fd2bba23f447
> --- /dev/null
> +++ b/arch/x86/boot/compressed/acpitb.h
> @@ -0,0 +1,50 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#include <linux/acpi.h>
> +
> +#define ACPI_MAX_TABLES                128
> +
> +/* Function to get ACPI SRAT table pointer. */
> +struct acpi_table_header *get_acpi_srat_table(void);
> +
> +#ifdef ACPI_BIG_ENDIAN
> +
> +#define ACPI_MOVE_64_TO_64(d, s) \
> +{((u8 *)(void *)(d))[0] = ((u8 *)(void *)(s))[7]; \
> +((u8 *)(void *)(d))[1] = ((u8 *)(void *)(s))[6]; \
> +((u8 *)(void *)(d))[2] = ((u8 *)(void *)(s))[5]; \
> +((u8 *)(void *)(d))[3] = ((u8 *)(void *)(s))[4]; \
> +((u8 *)(void *)(d))[4] = ((u8 *)(void *)(s))[3]; \
> +((u8 *)(void *)(d))[5] = ((u8 *)(void *)(s))[2]; \
> +((u8 *)(void *)(d))[6] = ((u8 *)(void *)(s))[1]; \
> +((u8 *)(void *)(d))[7] = ((u8 *)(void *)(s))[0]; }

Whats wrong with be64_to_cpu() ?

> +
> +#define ACPI_MOVE_16_TO_32(d, s) \
> +{(*(u32 *)(void *)(d)) = 0; \
> +((u8 *)(void *)(d))[2] = ((u8 *)(void *)(s))[1]; \
> +((u8 *)(void *)(d))[3] = ((u8 *)(void *)(s))[0]; }

Huch? 

> +
> +#else
> +#ifndef ACPI_MISALIGNMENT_NOT_SUPPORTED
> +
> +#define ACPI_MOVE_64_TO_64(d, s) \
> +{*(u64 *)(void *)(d) = *(u64 *)(void *)(s); }
> +
> +#define ACPI_MOVE_16_TO_32(d, s) \
> +{*(u32 *)(void *)(d) = *(u16 *)(void *)(s); }
> +
> +#else
> +#define ACPI_MOVE_64_TO_64(d, s) \
> +{((u8 *)(void *)(d))[0] = ((u8 *)(void *)(s))[0]; \
> +((u8 *)(void *)(d))[1] = ((u8 *)(void *)(s))[1]; \
> +((u8 *)(void *)(d))[2] = ((u8 *)(void *)(s))[2]; \
> +((u8 *)(void *)(d))[3] = ((u8 *)(void *)(s))[3]; \
> +((u8 *)(void *)(d))[4] = ((u8 *)(void *)(s))[4]; \
> +((u8 *)(void *)(d))[5] = ((u8 *)(void *)(s))[5]; \
> +((u8 *)(void *)(d))[6] = ((u8 *)(void *)(s))[6]; \
> +((u8 *)(void *)(d))[7] = ((u8 *)(void *)(s))[7]; }

And why doees this have to be done bytewise? Some comments would be
helpful.

Thanks,

	tglx