linux-kernel - Re: [RFC PATCH 1/2] ARM: mstar: Add header with macros for RIU register access

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Date:   Fri, 23 Apr 2021 23:02:42 +0900
From:   Daniel Palmer <daniel@...f.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     SoC Team <soc@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Olof Johansson <olof@...om.net>, Willy Tarreau <w@....eu>
Subject: Re: [RFC PATCH 1/2] ARM: mstar: Add header with macros for RIU
 register access

Hi Arnd,

On Fri, 23 Apr 2021 at 22:48, Arnd Bergmann <arnd@...nel.org> wrote:
>
> The __iomem token comes after the type, so this should be 'void __iomem *'.
>

Bit of copy/paste fail. Fixed.

> > +       return readw_relaxed(reg + 4) << 16 | readw_relaxed(reg);
>
> This should probably be using 'readw' instead of 'readw_relaxed'. If you
> absolutely need to use one of the relaxed accessors somewhere,
> better add both sets and make sure drivers use the non-relaxed version
> by default.

I'll add a relaxed/non-relaxed version of each.
Because of the heavy memory barrier to access one 32 bit register
we'll hit the barrier twice in the non-relaxed version.
And we don't need to hit the barrier at all because it doesn't
actually matter for IO. Is there something better I can do there?

> Maybe both types of accessors can be in a single header.

That makes sense. I'll merge them. Would this header be something that
could go in alone without anything that uses them in mainline right
now?

Thanks,

Daniel