[meta-freescale] SOC_FAMILY Rework

[Daiane Angolini]

We have today the following SOC_FAMILY tree (for meta-fsl-arm)

i.MX -> mx3 -> mx31;
i.MX -> mx3 -> mx35;
i.MX -> mx5 -> mx51;
i.MX -> mx5 -> mx53;
i.MX -> mx6 -> mx6dl;
i.MX -> mx6 -> mx6q;
i.MX -> mx6 -> mx6sl;
i.MX -> mx6 -> mx6sx;
i.MX -> mxs -> mx23;
i.MX -> mxs -> mx28;
Layerscape -> ls102xa;
Vybrid -> vf -> vf50;
Vybrid -> vf -> vf60;

Where i.MX, Layerscape and Vybrid are only included for visual
purposes, not being a real OVERRIDE today (the imx inclusion is a
pending patch in ML right now)

Some of the points I think is important to consider when choosing a
OVERRIDE tree is the SoC divergence and convergence. In i.MX case, we
have some obvious examples such as GPU type, existence of VPU, and
machine features such as CAN (although imx6 generally supports CAN,
there are some board with connector, and other without it).

In CAN case, CAN is a SoC feature enabled by the board or not. In WIFI
case, it’s only a board feature.

So, the points to rule the OVERRIDE is SoC features and board features.

Another important thing to keep in mind is the deepness. How deep
should be the OVERRIDE tree? Two or tree levels?

OVERRIDE should be used to cluster BSP packages and configurations
accordingly with SoC and machine features. Today the meta-fsl-arm BSP
packages can be seen in the table [1]. Most of packages are the same
for all i.MX boards (including kernel and u-boot not included in the
table), but some are very specific to a group of SoCs only (i.e.
fsl-alsa-plugins), and there is the case where a package is for only
one SoC Family, but has big inner segmentation (Vivante)

[1] https://github.com/Freescale/Documentation/blob/master/release-notes/source/soc-pkg-optimization.inc

The classic example of a crazy OVERRIDE is ‘mxs’. It was included in
the past to cluster imx23 and imx28 because they are the only 2 board
using imx-bootlets. Does ‘mxs’ make sense nowaday? Would imx6UL be
more related with imx28 than with imx6Q? Would imx6SX be clustered
with vf60?

Maybe, we can concentrate the OVERRIDE only around GPU and VPU. We
have an extensive segmentation of OVERRIDE for imx6, and a cluster for
all the SoCs without GPU (vf,layerscape?,imx2,imx3,imx6UL, imx7)

I only thing this is the right timing to review and rework SOC_FAMILY.
I'm i.MX biased, so I can only say about i.MX, would be glad to hear
feedback from Vybrid and QoirQ.

Regards,
Daiane