Messages in this thread | | | Subject | Re: [PATCH] Revert "regmap-mmio: Use native endianness for read/write" | From | Johannes Berg <> | Date | Tue, 26 Jan 2016 10:24:22 +0100 |
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On Tue, 2016-01-26 at 10:09 +0100, Arnd Bergmann wrote:
> Again, it's complicated: > > * We should probably add ioread64be()/iowrite64be() on *64bit* > architectures > for consistency with readq/writeq
Right.
> * 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.
> 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.
> However, we have some freedom at the regmap-mmio level, which we can > sanitize in 4.6 if we want to make it more consistent with the rest > of regmap. We have around 50 callers of {devm_,}regmap_init_mmio() > and almost all of them do not specify endianess but expect little- > endian behavior. We can change all existing instances to set > REGMAP_ENDIAN_NATIVE explicitly and change regmap_init_mmio() to > return an error if the caller does not specify a particular endianess > (big, little, native).
I'm not sure that we can, since regmap also takes the value from the DT directly, and it seems that a driver passing it would mean the DT value is no longer honoured?
johannes
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