linux-kernel - Re: [PATCH v2 1/3] x86/boot: add acpi rsdp address to setup

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Message-ID: <492e188d-6985-fb13-278b-46f096cb1b4b@suse.com>
Date:   Fri, 8 Dec 2017 09:52:45 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        x86@...nel.org, boris.ostrovsky@...cle.com, hpa@...or.com,
        tglx@...utronix.de, mingo@...hat.com, corbet@....net,
        rjw@...ysocki.net, lenb@...nel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 1/3] x86/boot: add acpi rsdp address to setup_header

On 08/12/17 09:48, Ingo Molnar wrote:
> 
> * Juergen Gross <jgross@...e.com> wrote:
> 
>>>> +Offset/size:	0x268/8
>>>> +Protocol:	2.14+
>>>> +
>>>> +  This field can be set by the boot loader to tell the kernel the
>>>> +  physical address of the ACPI RSDP table.
>>>> +
>>>> +  A value of 0 indicates the kernel should fall back to the standard
>>>> +  methods to locate the RSDP (search in EBDA/low memory).
>>>
>>> That's not the only method used: the ACPI RSDP address can also be discovered via 
>>> efi.rsdp20 and efi.rsdp, both of which appear to be 32-bit values.
>>
>> Sure, but this is valid for booting via EFI only.
> 
> Yeah, so what I tried to say is that the description as written is not fully 
> correct and triggered my pedantry:
> 
>  +  A value of 0 indicates the kernel should fall back to the standard
>  +  methods to locate the RSDP (search in EBDA/low memory).
> 
> To make it correct we need to either write less:
> 
>  +  A value of 0 indicates the kernel should fall back to the standard
>  +  methods to locate the RSDP.
> 
> or write more and make it open ended so it doesn't have to be extended with every 
> method of getting the RSDP that might be added in the future:
> 
>  +  A value of 0 indicates the kernel should fall back to the standard
>  +  methods to locate the RSDP (search in EBDA/low memory, get it from
>  +  EFI if present, etc.).
> 
> ... or so?

Aah, okay. I got your remark wrong then.

I think I'll go with the shorter variant.


Juergen