From: Arnd Bergmann > Sent: 17 May 2017 22:40 > > On Wed, May 17, 2017 at 11:16 PM, Chris Packham > <chris.pack...@alliedtelesis.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