linux-kernel - Re: [PATCH 02/11] MIPS: use virtual addresses from xkphys for MIPS64

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Message-Id: <32c626ee-5896-417a-bf57-b7e4216f1d25@app.fastmail.com>
Date:   Sun, 22 Oct 2023 12:52:04 +0100
From:   "Jiaxun Yang" <jiaxun.yang@...goat.com>
To:     "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
        "Gregory CLEMENT" <gregory.clement@...tlin.com>
Cc:     "paulburton@...nel.org" <paulburton@...nel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Vladimir Kondratiev" <vladimir.kondratiev@...el.com>,
        "Tawfik Bayouk" <tawfik.bayouk@...ileye.com>,
        "Alexandre Belloni" <alexandre.belloni@...tlin.com>,
        Théo Lebrun <theo.lebrun@...tlin.com>,
        "Thomas Petazzoni" <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 02/11] MIPS: use virtual addresses from xkphys for MIPS64



在2023年10月12日十月 下午4:34，Thomas Bogendoerfer写道：
> On Wed, Oct 04, 2023 at 06:10:29PM +0200, Gregory CLEMENT wrote:
>> From: Vladimir Kondratiev <vladimir.kondratiev@...el.com>
>> 
>> Now 64-bit MIPS uses 32-bit compatible segments KSEG0 and KSEG1
>> to trivially map first 1/2 GByte of physical memory. This memory
>> used to run kernel. This mean, one should have memory installed
>> in this area in order for Linux to work.
>> 
>> Kconfig CONFIG_USE_XKPHYS introduced; it adds support for kernel
>> to use virtual addresses from the XKPHYS segment for both cached
>> and uncached access. XKPHYS allows to access 2^48 bytes of
>> memory, thus allowing kernel to work with any memory
>> configuration.
>
> IMHO it doesn't make sense to introduce an option for a generic
> kernel, which then renders the generic kernel useless on all
> platforms other then yours.

Actually it won't. Many 64bit platforms do support load kernel to
XKPHYS, including boston and Loongson64, so it's still a generic
function.

IMO this patch won't break support for any generic platform.

>
> Please don't use generic, but setup a new platform for it. Hopefully
> we can get rid all of the weirdness in this patch.

Perhaps better to introduce a Kconfig option to allow manipulation of
kernel load address.

Thanks
- Jiaxun

>
> Thomas.
>
> -- 
> Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
> good idea.                                                [ RFC1925, 2.3 ]