Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [PATCH] Revert "regmap-mmio: Use native endianness for read/write" | Date | Tue, 26 Jan 2016 14:07:58 +0100 |
| |
On Tuesday 26 January 2016 10:24:22 Johannes Berg wrote: > On Tue, 2016-01-26 at 10:09 +0100, Arnd Bergmann wrote: > > * On 32-bit architectures, you generally cannot do 64-bit atomic I/O > > operations, and we have two implementations that do it > > nonatomically, > > depending on how a device is wired to the bus, see > > include/linux/io-64-nonatomic-{hi-lo,lo-hi}.h. > > I think we should just not go there for regmap unless we absolutely > > have to. > > regmap-mmio doesn't define the 8-bit accesses for 32-bit platforms, so > this is a non-issue, I think.
Ok, good.
> > There is still one open question about the defaults: I think we all > > agree that there is no way we can change the default for > > compatible="syscon" devices on ARM to from little-endian to cpu- > > endian, as that would break everything. Annotating the MIPS dts files > > as "cpu-endian" and leaving the rest to default to "little" is > > probably best here. > > Since regmap-mmio in practice was always little endian, we should > definitely make that consistent and explicit. Annotating those that > need special CPU-endian handling (MIPS with the byteswap engine) would > be best, I agree. > > Note that I made a mistake here yesterday - the *reg* for MMIO is still > NATIVE, while the *value* is LITTLE_ENDIAN. Looks like regmap-core can > byteswap both, which makes sense for I2C and similar busses.
I see, that's something I completely missed, and it's logical that the reg number must be native endian for MMIO but not for everything.
Arnd
| |