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

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Date:   Fri, 20 Jul 2018 17:35:24 +0800
From:   Chao Fan <fanc.fnst@...fujitsu.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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 Thu, Jul 19, 2018 at 05:19:43PM +0200, Thomas Gleixner wrote:
>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() ?

Hi tglx,

Thanks for your review.
ACPI_MOVE_64_TO_64 and ACPI_MOVE_16_TO_32 are copied from arch/x86/boot/compressed/acpitb.h
cause I though copying the old code is reliable.
I will delete these two definitions and only using le64_to_cpu and
le16_to_cpu may be enough(since ACPI table is in little endian).
And also add more comments in next version.

Thanks,
Chao Fan

>
>> +
>> +#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
>
>