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

From: Daniel Palmer <daniel@0x0f.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: SoC Team <soc@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Olof Johansson <olof@lixom.net>, Willy Tarreau <w@1wt.eu>
Subject: Re: [RFC PATCH 1/2] ARM: mstar: Add header with macros for RIU register access
Date: Fri, 23 Apr 2021 23:02:42 +0900	[thread overview]
Message-ID: <CAFr9PX=QeON1C_25tyNK1rWGm3A_Kc2Ad5qLUCfunmdHQUsv_g@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a3fkjy2YYwhmsFQt-MSyOh=1zf1wqzQB7usjsHbUBWdtQ@mail.gmail.com>

Hi Arnd,

On Fri, 23 Apr 2021 at 22:48, Arnd Bergmann <arnd@kernel.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