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From:   Junichi Nomura <j-nomura@ce.jp.nec.com>
To:     "bhe@redhat.com" <bhe@redhat.com>
CC:     Borislav Petkov <bp@alien8.de>, Dave Young <dyoung@redhat.com>,
        "fanc.fnst@cn.fujitsu.com" <fanc.fnst@cn.fujitsu.com>,
        "kasong@redhat.com" <kasong@redhat.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "kexec@lists.infradead.org" <kexec@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] x86/boot: Use EFI setup data if provided
Thread-Topic: [PATCH v2] x86/boot: Use EFI setup data if provided
Thread-Index: AQHU5R0gSF49+PGwf02T2oxnk4CVXaYgAhGAgAAQvICAAQMcAIAASZeA
Date:   Fri, 29 Mar 2019 03:34:23 +0000
Message-ID: <ed9b7ab0-c9c4-a0b8-f4b7-709e597c6f0b@ce.jp.nec.com>
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 <20190325231000.GA9184@jeru.linux.bs1.fc.nec.co.jp>
 <20190326135714.GG1867@zn.tnic> <20190327014852.GA3659@MiWiFi-R3L-srv>
 <73322ba9-e436-68db-7863-afd31607d969@ce.jp.nec.com>
 <20190328064343.GA1877@MiWiFi-R3L-srv>
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On 3/29/19 8:11 AM, bhe@redhat.com wrote:
> On 03/28/19 at 07:43am, Junichi Nomura wrote:
>>  /* Search EFI system tables for RSDP. */
>> -static acpi_physical_address efi_get_rsdp_addr(void)
>> +static acpi_physical_address __efi_get_rsdp_addr(unsigned long config_tables, unsigned int nr_tables, int size, bool efi_64)
> 
> Here parameter 'size' and 'efi_64' seems a little duplicated on
> functionality. Only passing efi_64 can deduce the size? Personal
> opinion.

Yes. But I'm not sure which is preferred.

The current code is:

__efi_get_rsdp_addr() {
        for (i = 0; i < nr_tables; i++) {
                config_tables += size;
                if (efi_64) {
                        efi_config_table_64_t *tbl = (efi_config_table_64_t *)config_tables;
                        // get guid and table
                } else {
                        efi_config_table_32_t *tbl = (efi_config_table_32_t *)config_tables;
                        // get guid and table
                }
                // check guid and return table if it's valid
        }
}

If we remove "size" parameter, that will become:

__efi_get_rsdp_addr() {
        for (i = 0; i < nr_tables; i++) {
                if (efi_64) {
                        efi_config_table_64_t *tbl;
                        config_tables += sizeof(efi_config_table_64_t);
                        tbl = (efi_config_table_64_t *)config_tables;
                        // get guid and table
                } else {
                        efi_config_table_32_t *tbl;
                        config_tables += sizeof(efi_config_table_32_t);
                        tbl = (efi_config_table_32_t *)config_tables;
                        // get guid and table
                }
                // check guid and return table if it's valid
        }
}

Or we could create 2 functions, __efi_get_rsdp_addr32() and __efi_get_rsdp_addr64(),
and let efi_get_rsdp_addr() to choose which one to use based on signature.

> It might be worth adding code comments here to tell why we only care
> about 64bit kexec booting?

I think so. I'll add a comment.

-- 
Jun'ichi Nomura, NEC Corporation / NEC Solution Innovators, Ltd.