Re: [PATCH net-next v3 7/8] net: dsa: lantiq_gswip: store switch API version in priv

The (anyway public) datasheets I have access to don't describe the VERSION
register at all. In the existing precompiler macros, however, you can see
that most-significant and least-significant byte are swapped. REV is
more significant than MOD:

#define GSWIP_VERSION                   0x013
#define  GSWIP_VERSION_REV_SHIFT        0
#define  GSWIP_VERSION_REV_MASK         GENMASK(7, 0)
#define  GSWIP_VERSION_MOD_SHIFT        8
#define  GSWIP_VERSION_MOD_MASK         GENMASK(15, 8)
#define   GSWIP_VERSION_2_0             0x100
#define   GSWIP_VERSION_2_1             0x021
#define   GSWIP_VERSION_2_2             0x122
#define   GSWIP_VERSION_2_2_ETC         0x022

Now I'd like to add
#define   GSWIP_VERSION_2_3             0x023

and then have a simple way to make features available starting from a
GSWIP_VERSION. Now in order for GSWIP_VERSION_2_3 to be greater than
GSWIP_VERSION_2_2, and GSWIP_VERSION_2_1 to be greater than
GSWIP_VERSION_2_0, the bytes need to be swapped.

I don't think the vendor even considered any specific order of the two
bytes but just defines them as separate 8-bit fields, considering it a
16-bit unsigned integer is my interpretation which came from the need for
comparability.

It would be good to put some of this into the commit message and
comments in the code. That the hardware has the 'major/minor' version
bytes in the wrong order preventing numerical comparisons. To make it
obvious, rather than use swap16(), maybe actually extract the major
and minor, and then construct the version in the form you want?

    Andrew