Messages in this thread | | | From | "" <> | Subject | RE: [PATCHv2 1/3] dt/bindings: Add the DT binding documentation for endianness | Date | Wed, 30 Apr 2014 05:08:46 +0000 |
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> > diff --git a/Documentation/devicetree/bindings/endianness/endianness.txt > b/Documentation/devicetree/bindings/endianness/endianness.txt > > new file mode 100644 > > index 0000000..64f1d5e > > --- /dev/null > > +++ b/Documentation/devicetree/bindings/endianness/endianness.txt > > @@ -0,0 +1,55 @@ > > +Device-Tree binding for device endianness > > + > > +The endianness mode of CPU & Device scenarios: > > + Index CPU Device > > + ------------------------ > > + 1 LE LE > > + 2 LE BE > > + 3 BE BE > > + 4 BE LE > > + > > +For one device driver, which will run in different scenarios above > > +on different SoCs using the devicetree, we need one way to simplify > > +this. > > + > > +Required properties: > > +- [prefix]-endian: this is one string property and must be one > > + of 'be', 'le' and 'native' if it is present. > > What exactly is the prefix? > > This file name and file heading implies this is a common endianness > binding, which it is not. There are many existing bindings that have > mechanisms for describing the endianness of components, and they have > settled on a different pattern. > > We already have many bindings with {big,little}-endian{,-*} boolean > properties. It would be better to take that common case and document > that as the standard way of doing things rather than inventing a > completely different mechanism. >
Well, yes, I'll follow your advice.
> > +The endianness mode: > > + 'le' : device is in little endian mode, > > + 'be' : device is in big endian mode, > > + 'native' : device is in the same endian mode with the CPU. > > What exactly do you mean by native? A device which always matches the > endianness of the CPU even if it changes? How common is that? >
It's originally based the regmap, and the 'native' is make no sense here, I'll reconstruct this.
> > + > > +Examples: > > +Scenario 1 : CPU in LE mode & device in LE mode. > > +dev: dev@40031000 { > > + compatible = "name"; > > + reg = <0x40031000 0x1000>; > > + ... > > + [prefix]-endian = 'native'; > > +}; > > If the device is LE, then surely we should describe the device as LE. > The kernel knows what endianness it is, might choose to change the CPU > endianness, but regardless can do the right thing. Telling it a device > is native is useless unless the device changes endianness with the CPU. >
Yes, you are right.
> > + > > +Scenario 2 : CPU in LE mode & device in BE mode. > > +dev: dev@40031000 { > > + compatible = "name"; > > + reg = <0x40031000 0x1000>; > > + ... > > + [prefix]-endian = 'be'; > > +}; > > + > > +Scenario 3 : CPU in BE mode & device in BE mode. > > +dev: dev@40031000 { > > + compatible = "name"; > > + reg = <0x40031000 0x1000>; > > + ... > > + [prefix]-endian = 'native'; > > +}; > > Likewise. > > Thanks, > Mark. >
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