[PATCH v2 35/65] clk: ux500: sysctrl: Add a determine_rate hook

[Lee Jones]

On Fri, 11 Nov 2022, Linus Walleij wrote:

> On Thu, Nov 10, 2022 at 2:05 PM Ulf Hansson <ulf.hansson at linaro.org> wrote:
> > On Thu, 10 Nov 2022 at 12:39, Linus Walleij <linus.walleij at linaro.org> wrote:
> > >
> > > On Thu, Nov 10, 2022 at 12:29 PM Ulf Hansson <ulf.hansson at linaro.org> wrote:
> > > > On Fri, 4 Nov 2022 at 14:32, Maxime Ripard <maxime at cerno.tech> wrote:
> > > > >
> > > > > The UX500 sysctrl "set_parent" clocks implement a mux with a set_parent
> > > > > hook, but doesn't provide a determine_rate implementation.
> > > > >
> > > > > This is a bit odd, since set_parent() is there to, as its name implies,
> > > > > change the parent of a clock. However, the most likely candidate to
> > > > > trigger that parent change is a call to clk_set_rate(), with
> > > > > determine_rate() figuring out which parent is the best suited for a
> > > > > given rate.
> > > > >
> > > > > The other trigger would be a call to clk_set_parent(), but it's far less
> > > > > used, and it doesn't look like there's any obvious user for that clock.
> > > >
> > > > If I recall correctly, that is the use case we did target for these
> > > > types of clocks. See sound/soc/ux500/ux500_ab85xx.c, for example.
> > >
> > > Hm I am trying to get that driver to work ... from time to time.
> > > It's just that ALSA SoC DT has changed to much that it turns out
> > > into a complete rewrite :/
> > >
> > > So in sound/soc/ux500/mop500_ab8500.c
> > > I see this:
> > >
> > >         status = clk_set_parent(drvdata->clk_ptr_intclk, clk_ptr);
> > >         if (status)
> > > (...)
> > >
> > > and there is elaborate code to switch between "SYSCLK" and
> > > "ULPCLK" (ulta-low power clock). Just like you say... however
> > > a clock named SYSCLK or ULPCLK does not appear in the
> > > code in drivers/clk/ux500 or any DT bindings so... it seems to
> > > be non-working for the time being.
> >
> > It's definitely not working, but the corresponding clocks ("ulpclk",
> > "intclk", "audioclk", etc) are being registered in ab8500_reg_clks().
> >
> > What seems to be missing is a DT conversion for these clocks, so they
> > can be consumed properly. Right?
> 
> Yeps that and a few more things, I have a scratch rewrite here:
> https://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-stericsson.git/log/?h=ux500-audio-rewrite
> 
> I remember Lee said he had audio working with the mainline kernel
> on Snowball at one point, unfortunately I think that was before we
> started with the DT conversions and then we probably broke it.

That was also 100 years ago. :)

But yes, it used to work at one point.

-- 
Lee Jones [李琼斯]