Re: [PATCH 6/9] clk: Allow the common clk framework to be selectable

[Greg Ungerer]

Hi Arnd, Stephen

On 6/4/20 5:35 pm, Arnd Bergmann wrote:
> On Mon, Apr 6, 2020 at 5:01 AM Stephen Boyd <sboyd@xxxxxxxxxx> wrote:
> > Quoting Arnd Bergmann (2020-04-05 05:45:20)
> > > On Sun, Apr 5, 2020 at 4:51 AM Stephen Boyd <sboyd@xxxxxxxxxx> wrote:
> > > > There's one snag with doing this, and that's making sure that randconfig
> > > > builds don't select this option when some architecture or platform
> > > > implements 'struct clk' outside of the common clk framework. Introduce a
> > > > new config option 'HAVE_LEGACY_CLK' to indicate those platforms that
> > > > haven't migrated to the common clk framework and therefore shouldn't be
> > > > allowed to select this new config option. Also add a note that we hope
> > > > one day to remove this config entirely.
> > >
> > > Good idea!
> > >
> > > I've looked through the individual ones and commented a bit on
> > > what I think may or may not happen with them.
> > >
> > > ralink SOC_MT7621 is the only one that I think you got wrong,
> > > as it already has common-clk support.
> >
> > Ah I missed that it was inside a big if RALINK. Thanks. I suppose I
> > should just remove the select then for that config and not worry about
> > the duplication of clkdev and common clk configs.
>
> Won't that cause build failures in those configurations that have
> both implementations?
>
> According to the Makefile, the clk.c file is built whenever CONFIG_MIPS_GIC
> is unset, so I think we need
>
>           select HAVE_LEGACY_CLK if !MIPS_GIC
>
> or maybe move the select into the per-chip configs that need it:
> RT288X, RT305X, RT3883, and MT7620.
>
> > > > diff --git a/arch/m68k/Kconfig.cpu b/arch/m68k/Kconfig.cpu
> > > > index 60ac1cd8b96f..bd2d29c22a10 100644
> > > > --- a/arch/m68k/Kconfig.cpu
> > > > +++ b/arch/m68k/Kconfig.cpu
> > >
> > >     text    data     bss     dec     hex filename
> > > 1934726 263616   83284 2281626 22d09a obj/vmlinux-before
> > > 1971989 266192   83308 2321489 236c51 obj/vmlinux-after
> > >
> > > The coldfire clock implementation looks rather simple compared
> > > to chips from the 2010s: most chips have only fixed clocks,
> > > and three of them have one of two registers of clock gates.
> > >
> > > It shouldn't be hard to convert, but enabling common-clk will
> > > cause a noticeable kernel size increase on the fairly limited
> > > hardware.
> > >
> > > Simply enabling COMMON_CLK in m5475evb_defconfig
> > > results in a 1.7% or 40KB growth in kernel size, plus there
> > > would be additional dynamic memory usage:
> > There could certainly be some work done to reduce the code size of the
> > CCF. I haven't looked but perhaps we could save some memory by making
> > the basic types selectable too and then push a bunch of kconfig updates
> > through for that.
>
> Right, that might help. Another possibility would be to support both
> the common clk layer and the custom clk implementation on coldfire
> until we remove the other custom implementations, by which point
> even fewer people will care about coldfire.
>
> Let's see what Geert and Greg think would be the best path for coldfire,
> maybe the added 40KB is less of a problem after all.

Losing another 40k is not ideal, but not the end of the world.
It would not stop me running it on any platforms I regularly
run on. For sure some of the really old hardware just doesn't
have the RAM to spare.

Any way, I say we have to move forward and and move to using
the common clock framework for ColdFire sooner than later.

Regards
Greg