Re: [PATCH v4 3/4] clk: spacemit: Add clock support for Spacemit K1 SoC

[Haylen Chu <heylenay@4d2.org>]

On Thu, Feb 13, 2025 at 10:04:10PM -0600, Alex Elder wrote:
> On 1/3/25 3:56 PM, Haylen Chu wrote:
> > The clock tree of K1 SoC contains three main types of clock hardware
> > (PLL/DDN/MIX) and is managed by several independent controllers in
> > different SoC parts (APBC, APBS and etc.), thus different compatible
> > strings are added to distinguish them.
> > 
> > Some controllers may share IO region with reset controller and other low
> > speed peripherals like watchdog, so all register operations are done
> > through regmap to avoid competition.
> > 
> > Signed-off-by: Haylen Chu <heylenay@4d2.org>
> 
> This is a really big patch (over 3000 lines), and a fairly large
> amount of code to review.  But I've given it a really thorough
> read and I have a *lot* of review comments for you to consider.
> 
> First, a few top-level comments.
> - This driver is very comprehensive.  It represents essentially
>   *all* of the clocks in the tree diagram shown here:
> https://developer.spacemit.com/resource/file/images?fileName=DkWGb4ed7oAziVxE6PIcbjTLnpd.png
>   (I can tell you what's missing but I don't think it matters.)
> - In almost all cases, the names of the clocks match the names
>   shown in that diagram, which is very helpful.
> - All of the clocks are implemented using "custom" clock
>   implementations.  I'm fairly certain that almost all of
>   them can use standard clock framework types instead
>   (fixed-rate, fixed-factor, fractional-divider, mux, and
>   composite).  But for now I think there are other things
>   more important to improve.
> - A great deal of my commentary below is simply saying that the
>   code is more complex than necessary.  Some simple (though
>   widespread) refactoring would improve things a lot.  And
>   some of the definitions can be done without having to
>   specify nearly so many values.
> - Much of what might be considered generality in the
>   implementation actually isn't needed, because it isn't used.
>   This is especially true given that there are essentially no
>   clocks left unspecified for the K1 SoC.
> - Once the refactoring I suggest has been done, I expect
>   that more opportunities for simplification and cleanup will
>   become obvious; we'll see.
> - I suggest these changes because the resulting simplicity
>   will make the code much more understandable and maintainable
>   in the long term.  And if it's simpler to understand, it
>   should be easier for a maintainer to accept.
> 
> I'm not going to comment on the things related to Device Tree
> that have already been mentioned, nor on the Makefile or Kconfig,
> etc.  I'm focusing just on the code.
> 
> > ---
> >   drivers/clk/Kconfig               |    1 +
> >   drivers/clk/Makefile              |    1 +
> >   drivers/clk/spacemit/Kconfig      |   20 +
> >   drivers/clk/spacemit/Makefile     |    5 +
> >   drivers/clk/spacemit/ccu-k1.c     | 1747 +++++++++++++++++++++++++++++
> >   drivers/clk/spacemit/ccu_common.h |   51 +
> >   drivers/clk/spacemit/ccu_ddn.c    |  140 +++
> >   drivers/clk/spacemit/ccu_ddn.h    |   84 ++
> >   drivers/clk/spacemit/ccu_mix.c    |  304 +++++
> >   drivers/clk/spacemit/ccu_mix.h    |  309 +++++
> >   drivers/clk/spacemit/ccu_pll.c    |  189 ++++
> >   drivers/clk/spacemit/ccu_pll.h    |   80 ++
> >   12 files changed, 2931 insertions(+)
> >   create mode 100644 drivers/clk/spacemit/Kconfig
> >   create mode 100644 drivers/clk/spacemit/Makefile
> >   create mode 100644 drivers/clk/spacemit/ccu-k1.c
> >   create mode 100644 drivers/clk/spacemit/ccu_common.h
> >   create mode 100644 drivers/clk/spacemit/ccu_ddn.c
> >   create mode 100644 drivers/clk/spacemit/ccu_ddn.h
> >   create mode 100644 drivers/clk/spacemit/ccu_mix.c
> >   create mode 100644 drivers/clk/spacemit/ccu_mix.h
> >   create mode 100644 drivers/clk/spacemit/ccu_pll.c
> >   create mode 100644 drivers/clk/spacemit/ccu_pll.h
> > 

...

> > diff --git a/drivers/clk/spacemit/ccu-k1.c b/drivers/clk/spacemit/ccu-k1.c
> > new file mode 100644
> > index 000000000000..6fb0a12ec261
> > --- /dev/null
> > +++ b/drivers/clk/spacemit/ccu-k1.c

...

> The next set of clocks differ from essentially all others, in that
> they don't encode their frequency in the name.  I.e., I would expect
> the first one to be named pll1_d2_1228p8.

I found this change may not be possible: with the frequency appended,
their names conflict with another set of MPMU gates.

> 
> > +static CCU_GATE_FACTOR_DEFINE(pll1_d2, "pll1_d2", CCU_PARENT_HW(pll1),
> > +			      APB_SPARE2_REG,
> > +			      BIT(1), BIT(1), 0, 2, 1, 0);
> > +static CCU_GATE_FACTOR_DEFINE(pll1_d3, "pll1_d3", CCU_PARENT_HW(pll1),
> > +			      APB_SPARE2_REG,
> > +			      BIT(2), BIT(2), 0, 3, 1, 0);
> > +static CCU_GATE_FACTOR_DEFINE(pll1_d4, "pll1_d4", CCU_PARENT_HW(pll1),
> > +			      APB_SPARE2_REG,
> > +			      BIT(3), BIT(3), 0, 4, 1, 0);
> > +static CCU_GATE_FACTOR_DEFINE(pll1_d5, "pll1_d5", CCU_PARENT_HW(pll1),
> > +			      APB_SPARE2_REG,
> > +			      BIT(4), BIT(4), 0, 5, 1, 0);
> > +static CCU_GATE_FACTOR_DEFINE(pll1_d6, "pll1_d6", CCU_PARENT_HW(pll1),
> > +			      APB_SPARE2_REG,
> > +			      BIT(5), BIT(5), 0, 6, 1, 0);
> > +static CCU_GATE_FACTOR_DEFINE(pll1_d7, "pll1_d7", CCU_PARENT_HW(pll1),
> > +			      APB_SPARE2_REG,
> > +			      BIT(6), BIT(6), 0, 7, 1, 0);
> > +static CCU_GATE_FACTOR_DEFINE(pll1_d8, "pll1_d8", CCU_PARENT_HW(pll1),
> > +			      APB_SPARE2_REG,
> > +			      BIT(7), BIT(7), 0, 8, 1, 0);
> > +

...

> > +/*	MPMU clocks start	*/

...

> > +static CCU_GATE_DEFINE(pll1_d3_819p2, "pll1_d3_819p2", CCU_PARENT_HW(pll1_d3),
> > +		       MPMU_ACGR,
> > +		       BIT(14), BIT(14), 0, 0);
> > +
> > +static CCU_GATE_DEFINE(pll1_d2_1228p8, "pll1_d2_1228p8", CCU_PARENT_HW(pll1_d2),
> > +		       MPMU_ACGR,
> > +		       BIT(16), BIT(16), 0, 0);

Here're the conflicts.

Although they don't happen on all the clocks, I prefer to keep the clock
names as is for now to keep the consistency.

Thanks,
Haylen Chu