linux-kernel - Re: [PATCH v2 02/11] mm: ioremap: fixup the physical address and page prot

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Date:   Tue, 23 Aug 2022 05:33:45 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Baoquan He <bhe@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "agordeev@...ux.ibm.com" <agordeev@...ux.ibm.com>,
        "wangkefeng.wang@...wei.com" <wangkefeng.wang@...wei.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 02/11] mm: ioremap: fixup the physical address and page
 prot



Le 23/08/2022 à 03:19, Baoquan He a écrit :
> On 08/22/22 at 06:30am, Christophe Leroy wrote:
>>
>>
>> Le 20/08/2022 à 02:31, Baoquan He a écrit :
>>> On some architectures, the physical address need be fixed up before
>>> doing mapping, e.g, parisc. And on architectures, e.g arc, the
>>> parameter 'prot' passed into ioremap_prot() need be adjusted too.
>>>
>>> In oder to convert them to take GENERIC_IOREMAP method, we need wrap
>>> the address fixing up code and page prot adjusting code into arch_ioremap()
>>> and pass the new address and 'prot' out for ioremap_prot() handling.
>>
>> Is it really the best approach ? Wouldn't it be better to have helpers
>> to do that, those helpers being called by the ioremap_prot(), instead of
>> doing it inside the arch_ioremap() function ?
> 
> This is suggested too by Alexander during his v1 reviewing. I tried, but
> feel the current way taken in this patchset is better. Because not all
> architecutres need the address fix up, only parisc, and only few need
> adjust the 'prot'. Introducing other helpers seems too much, that only
> increases the complexity of of ioremap() and the generic GENERIC_IOREMAP
> method for people to understand and take.

I can't understand. Why is it difficult to do something like:

#ifndef ioremap_adjust_prot
static inline unsigned long ioremap_adjust_prot(unsigned long flags)
{
	return flags;
}
#endif

Then for arc you do

static inline unsigned long ioremap_adjust_prot(unsigned long flags)
{
	return pgprot_val(pgprot_noncached(__pgprot(flags)));
}
#define ioremap_adjust_prot ioremap_adjust_prot


By the way, could be a good opportunity to change ioremap_prot() flags 
type from unsigned long to pgprot_t

> 
>>
>>>
>>> This is a preparation patch, no functionality change.
>>
>> Could this be squashed into previous patch ?
> 
> Yep, will do. Thanks.
>