Re: [PATCH 1/2] can: flexcan: Remodel FlexCAN register r/w APIs for big endian FlexCAN controllers.

[Marc Kleine-Budde <mkl-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>]

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On 11/10/2017 05:32 PM, Pankaj Bansal wrote:
> Thanks for sharing the video and slides. It was really helpful. But I
> would still like to solve this problem using device tree property. My
> rationale behind it is that, if a platform designer uses same IP
> block whose support is present is linux kernel, but with different
> endianness. Then he would not need to add his platform data in each
> driver to support his platform in linux. He can just add endianness
> property in device tree and can use latest linux kernel right off the
> bat. This is also mentioned in
> "Documentation/devicetree/bindings/regmap/regmap.txt".
> 
> Regmap defaults to little-endian register access on MMIO based
> devices, this is by far the most common setting. On CPU
> architectures that typically run big-endian operating systems
> (e.g. PowerPC), registers can be defined as big-endian and must
> be marked that way in the devicetree.
> 
> This rule was apparently not followed in P1010RDB flexcan node.
> 
> To solve this problem, I suggest that we define 2 optional device
> tree properties for flexcan. little-endian : for powerpc
> architecture, if this property is defined then controller is little
> endian otherwise big endian (default) big-endian : for other
> architectures, if this property is defined then controller is big
> endian otherwise little endian (default)
> 
> Although the controller drivers should be architecture independent,
> but apparently there is no way around it in flexcan.

Please keep the endianess as default es stated in the comment in the driver:

>> /* Abstract off the read/write for arm versus ppc. This
>>  * assumes that PPC uses big-endian registers and everything
>>  * else uses little-endian registers, independent of CPU
>>  * endianness.
>>  */

See description of commit 0e4b949e6620 ("can: flexcan: fix flexcan
driver build for big endian on ARM and little endian on PowerPc") for
more information.

I'll not ACK a change in the driver, that's breaking PPC.

Marc

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