Re: [PATCH v2 2/3] soc: sifive: Add SiFive specific Cadence DDR controller driver

[Palmer Dabbelt]

On Sun, 06 Sep 2020 23:11:26 PDT (-0700), Christoph Hellwig wrote:
> On Mon, Sep 07, 2020 at 11:17:58AM +0530, Yash Shah wrote:
> > Add a driver to manage the Cadence DDR controller present on SiFive SoCs
> > At present the driver manages the EDAC feature of the DDR controller.
> > Additional features may be added to the driver in future to control
> > other aspects of the DDR controller.
>
> So if this is a generic(ish) Cadence IP block shouldn't it be named
> Cadence and made generic?  Or is the frontend somehow SiFive specific?

For some reason I thought we had a SiFive-specific interface to this, but I may
have gotten that confused with something else as it's been a while.  Someone
from SiFive would probably have a better idea, but it looks like the person I'd
ask isn't thereany more so I'm all out of options ;)

It looks like there was a very similar driver posted by Dhananjay Kangude from
Cadence in April: https://lkml.org/lkml/2020/4/6/358 .  Some of the register
definitions seem to be different, but the code I looked at is very similar so
there's at least some bits that could be shared.  I found a v4 of that patch
set, but that was back in May: https://lkml.org/lkml/2020/5/11/912 .  It
alludes to a v5, but I can't find one.  I've added Dhananjay, maybe he knows
what's up?

I don't know enough about the block to know if the subtle difference in
register names/offsets means.  They look properly jumbled up (ie, not just an
offset), so maybe there's just different versions or that's the SiFive-specific
part I had bouncing around my head?  Either way, it seems like one driver with
some simple configuration could handle both of these -- either sticking the
offsets in the DT (if they're going to be different everywhere) or by coming up
with some version sort of thing (if there's a handful of these).

I'm now also a bit worried about the provenace of this code.  The two drivers
are errily similar -- for example, the variable definitions in handle_ce()

      u64 err_c_addr = 0x0;
      u64 err_c_data = 0x0;
      u32 err_c_synd, err_c_id;
      u32 sig_val_l, sig_val_h;

are exactly the same.