linux-kernel - RE: [PATCH 3/3] EDAC: mv64x60: replace in_le32/out

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Date:   Fri, 19 May 2017 14:01:04 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Arnd Bergmann' <arnd@...db.de>,
        Chris Packham <Chris.Packham@...iedtelesis.co.nz>
CC:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>
Subject: RE: [PATCH 3/3] EDAC: mv64x60: replace in_le32/out_le32 with
 ioread32/iowrite32

From: Arnd Bergmann
> Sent: 17 May 2017 22:40
> 
> On Wed, May 17, 2017 at 11:16 PM, Chris Packham
> <Chris.Packham@...iedtelesis.co.nz> wrote:
> > On 18/05/17 06:18, Borislav Petkov wrote:
> > One thing I would like confirmation on is is in_le32 -> ioread32 the
> > correct change? I tossed up between ioread32 and readl. Looking at
> > mv643xx_eth.c which supports both the MV643XX and Orion it's using readl
> > so perhaps I should be using that.
> 
> There is no easy answer: on powerpc, readl is used for PCI,
> while in_le32 is used for on-chip devices, so in_le32 is the
> right one in principle. The main difference is that readl can
> work with CONFIG_EEH on pseries, but in_le32 is cheaper.
> 
> On ARM and most other architectures, readl is used for both
> PCI and on-chip devices, so that's what portable code tends
> to use.
> 
> ioread32 is required to behave the same way as readl
> on all __iomem pointers returned from ioremap(), but
> is an extern function on powerpc and can be more
> expensive when CONFIG_GENERIC_IOMAP is set.

What about x86?
Isn't ioread32() an extern function that checks for 'io' addresses
than need 'inb' (etc) instructions rather than memory ones.
If we know a PCI slave isn't 'io' should be be using ioread32() or readl()?
Don't some architectures have different enforced barriers in both these?

	David