> Subject: Re: [PATCHv4 2/2] regmap: add DT endianness binding support.
>
> On Fri, May 09, 2014 at 03:04:33AM +0100, Xiubo Li wrote:
> > For many drivers which will support rich endianness of CPU<-->Dev
> > need define DT properties by itself without the binding support.
> >
> > The endianness using regmap:
> > Index CPU Device Endianess flag for DT bool property
> > ------------------------------------------------------------
> > 1 LE LE -
> > 2 LE BE 'big-endian-{val,reg}'
> > 3 BE BE -
> > 4 BE LE 'little-endian-{val,reg}'
>
> Get rid of the CPU column. It has precisely _nothing_ to do with the
> device.
>
> If you happen to have a device that can be integrated with varying
> endianness, the endianness should be described regardless of whether
> this happens to be the same as the CPU endianness. The kernel can then
> choose to do the right thing regardless.
>
> Assuming LE or BE by default is sane if most implementations are one
> rather than the other. Probing and figuring it out dynamically is also
> fine. Assuming that it's the same as the kernel is broken in general,
> and should be avoided -- those cases _require_ a *-endian property to
> work if the CPU can function in either endianness.
>
Yes, If my understanding is correct, if we need inverting the bytes order,
should be add one property here, regardless of the CPU's endianesses.
> > Please see the following documetation for detail:
> > Documentation/devicetree/bindings/endianness/endianness.txt
>
> I don't think this is sufficient. That document describes the preferred
> idiom, not the meaning w.r.t. a specific binding.
>
> [...]
>
> > + case REGMAP_ENDIAN_REG:
> > + if (of_property_read_bool(np, "big-endian-reg"))
> > + *endian = REGMAP_ENDIAN_BIG;
> > + else if (of_property_read_bool(np, "little-endian-reg"))
> > + *endian = REGMAP_ENDIAN_LITTLE;
>
> While this follows the guidelines you've added, context is still
> required to understand precisely what this means. We need a binding
> document describing what *-endian-reg means for this binding (i.e. what
> does -reg cover? All registers? some? buffers?).
>
Yes, for now the 'reg' is for all registers of the device.
And the 'val' is for all the values and buffers of the device.
@Mark Brown,
Do you have any correction here ?
> Imagine I added a little-endian-foo property. You'd be able to reason
> that something is little endian, but you'd have no idea of precisely
> what without reading documentation or code. As not everyone wants to
> read several thousand lines of Linux kernel code to write a dts we
> require documentation.
>
@Mark Rutland, @Mark Brown,
Yes, where should I locate the documentation ?
Is Documentation/devicetree/bindings/regmap/ okay ?
Thanks,
BRs
Xiubo
> > + case REGMAP_ENDIAN_VAL:
> > + if (of_property_read_bool(np, "big-endian-val"))
> > + *endian = REGMAP_ENDIAN_BIG;
> > + else if (of_property_read_bool(np, "little-endian-val"))
> > + *endian = REGMAP_ENDIAN_LITTLE;
>
> Likewise.
>
> Cheers,
> Mark.
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