linux-kernel - Re: [PATCH v3 00/27] kill devm_ioremap

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Message-ID: <6c0ade63-f4d3-d44d-c622-b091eb2ba902@huawei.com>
Date:   Mon, 25 Dec 2017 09:09:10 +0800
From:   Yisheng Xie <xieyisheng1@...wei.com>
To:     christophe leroy <christophe.leroy@....fr>,
        Guenter Roeck <linux@...ck-us.net>,
        Greg KH <gregkh@...uxfoundation.org>
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Subject: Re: [PATCH v3 00/27] kill devm_ioremap_nocache

hi Christophe and Greg,

On 2017/12/24 16:55, christophe leroy wrote:
> 
> 
> Le 23/12/2017 à 16:57, Guenter Roeck a écrit :
>> On 12/23/2017 05:48 AM, Greg KH wrote:
>>> On Sat, Dec 23, 2017 at 06:55:25PM +0800, Yisheng Xie wrote:
>>>> Hi all,
>>>>
>>>> When I tried to use devm_ioremap function and review related code, I found
>>>> devm_ioremap and devm_ioremap_nocache is almost the same with each other,
>>>> except one use ioremap while the other use ioremap_nocache.
>>>
>>> For all arches?  Really?  Look at MIPS, and x86, they have different
>>> functions.
>>>
>>
>> Both mips and x86 end up mapping the same function, but other arches don't.
>> mn10300 is one where ioremap and ioremap_nocache are definitely different.
> 
> alpha: identical
> arc: identical
> arm: identical
> arm64: identical
> cris: different        <==
> frv: identical
> hexagone: identical
> ia64: different        <==
> m32r: identical
> m68k: identical
> metag: identical
> microblaze: identical
> mips: identical
> mn10300: different     <==
> nios: identical
> openrisc: different    <==
> parisc: identical
> riscv: identical
> s390: identical
> sh: identical
> sparc: identical
> tile: identical
> um: rely on asm/generic
> unicore32: identical
> x86: identical
> asm/generic (no mmu): identical

Wow, that's correct, sorry for I have just checked the main archs, I means
x86,arm, arm64, mips.

However, I stall have no idea about why these 4 archs want different ioremap
function with others. Drivers seems cannot aware this? If driver call ioremap
want he really want for there 4 archs, cache or nocache?

> 
> So 4 among all arches seems to have ioremap() and ioremap_nocache() being different.
> 
> Could we have a define set by the 4 arches on which ioremap() and ioremap_nocache() are different, something like HAVE_DIFFERENT_IOREMAP_NOCACHE ?

Then, what the HAVE_DIFFERENT_IOREMAP_NOCACHE is uesed for ?

Thanks
Yisheng
> 
> Christophe
> 
>>
>> Guenter
>>
>>>> While ioremap's
>>>> default function is ioremap_nocache, so devm_ioremap_nocache also have the
>>>> same function with devm_ioremap, which can just be killed to reduce the size
>>>> of devres.o(from 20304 bytes to 18992 bytes in my compile environment).
>>>>
>>>> I have posted two versions, which use macro instead of function for
>>>> devm_ioremap_nocache[1] or devm_ioremap[2]. And Greg suggest me to kill
>>>> devm_ioremap_nocache for no need to keep a macro around for the duplicate
>>>> thing. So here comes v3 and please help to review.
>>>
>>> I don't think this can be done, what am I missing?  These functions are
>>> not identical, sorry for missing that before.

Never mind, I should checked all the arches, sorry about that.

>>>
>>> thanks,
>>>
>>> greg k-h
>>>
>>
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