linux-kernel - RE: [PATCH v2 01/11] mm/ioremap: change the return value of io[re|un]map

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Message-ID: <b193efbff3a74343839c3dee1702f73c@AcuMS.aculab.com>
Date:   Wed, 24 Aug 2022 08:16:54 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Christophe Leroy' <christophe.leroy@...roup.eu>,
        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 01/11] mm/ioremap: change the return value of
 io[re|un]map_allowed and rename

From: Christophe Leroy
> Sent: 23 August 2022 16:26
> 
> Le 23/08/2022 à 17:14, Baoquan He a écrit :
> > On 08/23/22 at 05:24am, Christophe Leroy wrote:
> >>
> >>
> >> Le 23/08/2022 à 02:20, Baoquan He a écrit :
> >>> On 08/22/22 at 06:25am, Christophe Leroy wrote:
> >>>>
> >>>>
> >>>> Le 20/08/2022 à 02:31, Baoquan He a écrit :
> >>>>> In some architectures, there are ARCH specifici io address mapping
> >>>>> handling when calling ioremap() or ioremap_prot(), e.g, arc, ia64,
> >>>>> openrisc, s390, sh.
> >>>>>
> >>>>> In oder to convert them to take GENERIC_IOREMAP method, we need change
> >>>>> the return value of hook ioremap_allowed() and iounmap_allowed().
> >>>>> Meanwhile, rename them to arch_ioremap() and arch_iounmap() to reflect
> >>>>> their current behaviour.
> >>>
> >>> Thanks for reviewing.
> >>>
> >>>>
> >>>> Please don't just say you need to change the return value. Explain why.
> >>>
> >>> The 1st paragraph and the sentence 'In oder to convert them to take
> >>> GENERIC_IOREMAP method' tell the reason, no?
> >>
> >> What I would like to read is _why_ you need to change the return value
> >> in order to convert to GENERIC_IOREMAP
> >
> > I rephrase the log as below, it's OK to you? Or please help check and
> > tell what I need to improve to better explain the reason.
> >
> > ====
> > The current io[re|un]map_allowed() hooks are used to check if the
> > io[re|un]map() actions are qualified to proceed when taking
> > GENERIC_IOREMAP way to do ioremap()/iounmap(). Otherwise io[re|un]map()
> > will return NULL.
> >
> > On some architectures like arc, ia64, openris, s390, sh, there are
> > ARCH specific io address mapping to translate the passed in physical
> > address to io address when calling ioremap(). In order to convert
> > these architectures to take GENERIC_IOREMAP way to ioremap(), we need
> > change the return value of hook ioremap_allowed() and iounmap_allowed().
> > With the change, we can move the architecture specific io address
> > mapping into ioremap_allowed() hook, and give the mapped io address
> > out to let ioremap_prot() return it. While at it, rename the hooks to
> > arch_ioremap() and arch_iounmap() to reflect their new behaviour.
> > ====
> >
> 
> That looks more in line with the type of explanation I foresee in the
> commit message, thanks.

I think you also need to summarise the change itself.
If the success/fail return actually changes then you really
need to change something so the compiler errors unchanged code.
Otherwise it is a complete recipe for disaster.

	David

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