Re: [RFC PATCH v4 net-next 00/23] add support for VSC75XX control over SPI

On Tue, Nov 16, 2021 at 07:32:08AM -0800, Colin Foster wrote:

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One thing to note: I've been following a pattern of adding "offset"
variables to these drivers. I'm looking for feedback here, because I
don't like it - however I feel like it is the "least bad" interface I
could come up with. 

Specifically, ocelot has a regmap for GCB. ocelot-pinctrl would create a
smaller regmap at an address of "GCB + 0x34".

There are three options I saw here:
1. Have vsc7512_spi create a new regmap at GCB + 0x34 and pass that to
ocelot-pinctrl
2. Give ocelot-pinctrl the concept of a "parent bus" by which it could
request a regmap. 
3. Keep the same GCB regmap, but pass in 0x34 as an offset.


I will admit that option 2 sounds very enticing, but I don't know if
that type of interaction exists. If not, implementing it is probably
outside the scope of a first patch set. As such, I opted for option 3.

I think that type of interaction is called "mfd", potentially even "syscon".

Before diving in, I'd come across mfd and thought that might be the
answer. I'll reconsider it now that I have several months of staring at
kernel code under my belt. Maybe an mfd that does SPI setup and chip
resetting. Then I could remove all SPI code from ocelot_vsc7512_spi.

That sounds acceptable to me.