[PATCH 0/3] ARM: vexpress: TC2 MCPM/SPC cleanups

[Lorenzo Pieralisi]

On Tue, Aug 06, 2013 at 05:19:53PM +0100, Pawel Moll wrote:
> On Mon, 2013-08-05 at 10:47 +0100, Lorenzo Pieralisi wrote:
> > For the bindings, you are right, how about this (commit log written just
> > for the sake of it, it should be squashed in Nico's original series) ?
> 
> So I finally sat down and did what I should have done long time ago...
> Read the spec ;-)
> 
> SCC is (was?) mainly used to set initial conditions for the cores,
> interconnect and all the other bits and pieces inside the test chip. It
> could be considered an equivalent of the classic "boot mode" pins, but
> as test chips have many more of them comparing to the normal SOCs, the
> data is being "injected" to the chip in a serial fashion *before* the
> main reset is being de-asserted. This is done by an external entity,
> namely the DCC (daughterboard configuration controller, so simply a
> microcontroller living next to the test chip). Why is this detail
> important at all? Because traditionally the SCC was *not* available in
> the normal memory map, otherwise it would be a perfect candidate for
> the . In order to change anything one had to go through the usual
> Versatile Express config infrastructure. Fortunately there was no need
> to do this at all...
> 
> And here comes the V2P-CA15_A7, also known as TC2 ;-) where the
> interface was re-(or ab-?)used as a "convenient" communication channel
> between the test chip and the microcontroller. And the SPC is even
> described as "being merged" with the SCC. Uh...

Yes, the "merging" of SCC and SPC is the root cause of this hopefully happy
ended story, they lumped together pieces of HW that should have been kept
separate.

> Now, the bottom line. How about keeping the driver look for
> "arm,vexpress-spc,v2p-ca15_a7" because it's a driver for the SPC bit
> after all and doing the following in the tree:
> 
> scc at 7fff0000 {
> 	compatible = "arm,vexpress-scc,v2p-ca15_a7", "arm,vexpress-scc";
> 	reg = <0x7fff0000 0x1000>;
> 	interrupts = <0 95 4>;
> 
> 	spc at b00 {
> 		compatible = "arm,vexpress-spc,v2p-ca15_a7", "arm,vexpress-spc";
> 		reg = <0xb00 0x100>;
> 	};
> };
> 
> This, I believe, would represent the actual situation, require no change
> in the driver (except for the retirement of SPC_BASE which is good :-)
> and allowed as, if and when necessary, to drive the SCC as a MFD/syscon
> device.

I do need some SCC registers to check the cluster ID against the MPIDR in
order to carry out powerdown operations. So if we do what you suggest we have
to change the driver, I would avoid doing that at this stage.

> Does it make some sense?

Well, it does but it complicates our lives for not much IMHO (and Olof
mentioned that in the cover letter). I still need to map the SCC as a
whole to read some IDs registers as I mentioned. We can find a way to make
SPC part of a MFD device later on.

Lorenzo