Re: [RFT 00/13] iomap: Constify ioreadX() iomem argument

From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Krzysztof Kozlowski <krzk@kernel.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Rich Felker <dalias@libc.org>, Jiri Slaby <jirislaby@gmail.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	David Airlie <airlied@linux.ie>,
	nouveau@lists.freedesktop.org,
	DRI Development <dri-devel@lists.freedesktop.org>,
	virtualization@lists.linux-foundation.org,
	"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
	Paul Mackerras <paulus@samba.org>,
	Linux-Arch <linux-arch@vger.kernel.org>,
	Dave Jiang <dave.jiang@intel.com>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Helge Deller <deller@gmx.de>,
	Linux-sh list <linux-sh@vger.kernel.org>,
	Alexey Brodkin <abrodkin@synopsys.com>,
	Ben Skeggs <bskeggs@redhat.com>, Dave Airlie <airlied@redhat.com>,
	Matt Turner <mattst88@gmail.com>,
	arcml <linux-snps-arc@lists.infradead.org>,
	Nick Kossifidis <mickflemm@gmail.com>,
	Allen Hubbe <allenbh@gmail.com>, Arnd Bergmann <arnd@arndb.de>,
	Jon Mason <jdmason@kudzu.us>,
	Ivan
Subject: Re: [RFT 00/13] iomap: Constify ioreadX() iomem argument
Date: Wed, 8 Jan 2020 09:35:54 +0100	[thread overview]
Message-ID: <2355489c-a207-1927-54cf-85c04b62f18f__3343.40829156048$1578473692$gmane$org@c-s.fr> (raw)
In-Reply-To: <CAJKOXPfq9vS4kSyx1jOPHBvi9_HjviRv0LU2A8ZwdmqgUuebHQ@mail.gmail.com>

Le 08/01/2020 à 09:18, Krzysztof Kozlowski a écrit :
> On Wed, 8 Jan 2020 at 09:13, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>>
>> Hi Krzysztof,
>>
>> On Wed, Jan 8, 2020 at 9:07 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>>> On Tue, Jan 7, 2020 at 5:53 PM Krzysztof Kozlowski <krzk@kernel.org> wrote:
>>>> The ioread8/16/32() and others have inconsistent interface among the
>>>> architectures: some taking address as const, some not.
>>>>
>>>> It seems there is nothing really stopping all of them to take
>>>> pointer to const.
>>>
>>> Shouldn't all of them take const volatile __iomem pointers?
>>> It seems the "volatile" is missing from all but the implementations in
>>> include/asm-generic/io.h.
>>
>> As my "volatile" comment applies to iowrite*(), too, probably that should be
>> done in a separate patch.
>>
>> Hence with patches 1-5 squashed, and for patches 11-13:
>> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
> 
> I'll add to this one also changes to ioreadX_rep() and add another
> patch for volatile for reads and writes. I guess your review will be
> appreciated once more because of ioreadX_rep()
> 

volatile should really only be used where deemed necessary:

https://www.kernel.org/doc/html/latest/process/volatile-considered-harmful.html

It is said: " ...  accessor functions might use volatile on 
architectures where direct I/O memory access does work. Essentially, 
each accessor call becomes a little critical section on its own and 
ensures that the access happens as expected by the programmer."

Christophe
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization