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From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Krzysztof Kozlowski <krzk@kernel.org>,
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Subject: Re: [RFT 00/13] iomap: Constify ioreadX() iomem argument
Date: Wed, 8 Jan 2020 09:43:04 +0100
Message-ID: <CAMuHMdV=-m-eN4rOa=XQhk2oBDZZwgXXMU6RMVQRVsc6ALyeoA@mail.gmail.com> (raw)
In-Reply-To: <2355489c-a207-1927-54cf-85c04b62f18f@c-s.fr>

Hi Christophe,

On Wed, Jan 8, 2020 at 9:35 AM Christophe Leroy <christophe.leroy@c-s.fr> wrote:
> 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:
> >> 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."

That is exactly the use case here: all above are accessor functions.

Why would ioreadX() not need volatile, while readY() does?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-07 16:52 Krzysztof Kozlowski
2020-01-07 16:52 ` [RFT 01/13] iomap: Constify ioreadX() iomem argument (as in generic implementation) Krzysztof Kozlowski
2020-01-07 16:52 ` [RFT 02/13] alpha: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 02/13] sh: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 03/13] alpha: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 03/13] sh: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 04/13] parisc: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 05/13] powerpc: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 06/13] arc: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 07/13] drm/mgag200: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 08/13] drm/nouveau: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 09/13] media: fsl-viu: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 10/13] net: wireless: ath5k: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 11/13] net: wireless: rtl818x: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 12/13] ntb: intel: " Krzysztof Kozlowski
2020-01-07 16:53 ` [RFT 13/13] virtio: pci: " Krzysztof Kozlowski
     [not found] ` <CAMuHMdW4ek0OYQDrrbcpZjNUTTP04nSbwkmiZvBmKcU=PQM9qA@mail.gmail.com>
     [not found]   ` <CAMuHMdUBmYtJKtSYzS_5u67hVZOqcKSgFY1rDGme6gLNRBJ_gA@mail.gmail.com>
     [not found]     ` <CAJKOXPfq9vS4kSyx1jOPHBvi9_HjviRv0LU2A8ZwdmqgUuebHQ@mail.gmail.com>
2020-01-08  8:35       ` [RFT 00/13] iomap: Constify ioreadX() iomem argument Christophe Leroy
2020-01-08  8:43         ` Geert Uytterhoeven [this message]
2020-01-08  8:48           ` Christophe Leroy
2020-01-08  8:44         ` Arnd Bergmann

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