Re: [PATCH v2 1/1] clk: samsung: exynos850: Register clocks early

From: Sam Protsenko <semen.protsenko@linaro.org>
To: Sylwester Nawrocki <s.nawrocki@samsung.com>
Cc: "Sumit Semwal" <sumit.semwal@linaro.org>,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-samsung-soc@vger.kernel.org,
	"Krzysztof Kozlowski" <krzysztof.kozlowski@canonical.com>,
	"Paweł Chmiel" <pawel.mikolaj.chmiel@gmail.com>,
	"Chanwoo Choi" <cw00.choi@samsung.com>,
	"Tomasz Figa" <tomasz.figa@gmail.com>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Stephen Boyd" <sboyd@kernel.org>,
	"Michael Turquette" <mturquette@baylibre.com>
Subject: Re: [PATCH v2 1/1] clk: samsung: exynos850: Register clocks early
Date: Sat, 20 Nov 2021 18:47:23 +0200	[thread overview]
Message-ID: <CAPLW+4nnyPAMRcAzDjJ-uygm8bjncNp_rTLKdY5cywcpf5vg=w@mail.gmail.com> (raw)
In-Reply-To: <fcc939e6-50b4-1847-c738-db940d0c5bd4@samsung.com>

On Sat, 20 Nov 2021 at 14:49, Sylwester Nawrocki <s.nawrocki@samsung.com> wrote:
>
> On 25.10.2021 18:12, Sam Protsenko wrote:
> > Some clocks must be registered before init calls. For example MCT clock
> > (from CMU_PERI) is needed for MCT timer driver, which is registered
> > with TIMER_OF_DECLARE(). By the time we get to core_initcall() used for
> > clk-exynos850 platform driver init, it's already too late. Inability to
> > get "mct" clock in MCT driver leads to kernel panic, as functions
> > registered with *_OF_DECLARE() can't do deferred calls. MCT timer driver
> > can't be fixed either, as it's acting as a clock source and it's
> > essential to register it in start_kernel() -> time_init().
> >
> > Let's register CMU_PERI clocks early, using CLK_OF_DECLARE_DRIVER(), and
> > do all stuff relying on "struct dev" object (like runtime PM and
> > enabling bus clock) later in platform driver probe. Basically
> > CLK_OF_DECLARE_DRIVER() matches CMU compatible, but clears OF_POPULATED
> > flag, which allows the same device to be matched again later.
>
> > Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
>
> >  drivers/clk/samsung/clk-exynos850.c | 17 +++++++++++++++--
> >  1 file changed, 15 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/clk/samsung/clk-exynos850.c b/drivers/clk/samsung/clk-exynos850.c
> > index 95e373d17b42..ecffa5c7a081 100644
> > --- a/drivers/clk/samsung/clk-exynos850.c
> > +++ b/drivers/clk/samsung/clk-exynos850.c
> > @@ -753,6 +753,15 @@ static const struct samsung_cmu_info peri_cmu_info __initconst = {
> >       .clk_name               = "dout_peri_bus",
> >  };
> >
> > +static void __init exynos850_cmu_peri_init(struct device_node *np)
> > +{
> > +     exynos850_init_clocks(np, peri_clk_regs, ARRAY_SIZE(peri_clk_regs));
> > +     samsung_cmu_register_one(np, &peri_cmu_info);
> > +}
> > +
> > +CLK_OF_DECLARE_DRIVER(exynos850_cmu_peri, "samsung,exynos850-cmu-peri",
> > +                   exynos850_cmu_peri_init);
> > +
> >  /* ---- CMU_CORE ------------------------------------------------------------ */
> >
> >  /* Register Offset definitions for CMU_CORE (0x12000000) */
> > @@ -920,8 +929,12 @@ static int __init exynos850_cmu_probe(struct platform_device *pdev)
> >       struct device_node *np = dev->of_node;
> >
> >       info = of_device_get_match_data(dev);
> > -     exynos850_init_clocks(np, info->clk_regs, info->nr_clk_regs);
> > -     samsung_cmu_register_one(np, info);
> > +
> > +     /* Early clocks are already registered using CLK_OF_DECLARE_DRIVER() */
> > +     if (info != &peri_cmu_info) {
> > +             exynos850_init_clocks(np, info->clk_regs, info->nr_clk_regs);
> > +             samsung_cmu_register_one(np, info);
> > +     }
>
> Don't you also need to register early CMU_TOP, which provides clocks
> for CMU_PERI? I'm afraid it might not work properly when you register
> CMU_PERI clocks early and only later in probe() you enable parent clock
> required for the already registered clocks to be usable.

Good point, I'll do that in v2. Not sure how I missed that dependency
point, but thank you for noticing that. Guess it only works for me
because clocks are already enabled in bootloader, and I'm using
"clk_ignore_unused" param for now.

> How about registering also CMU_TOP early and enabling parent clock
> also in OF_CLK_DECLARE init callback, i.e. using either OF_CLK_DECLARE
> or platform driver for a CMU?
>

If you mean doing clk_prepare_enable() for "dout_peri_bus" clock in
exynos850_cmu_peri_init(), I don't think it's possible. clk_get()
needs "struct device *dev", and we only have that in platform driver
probe. Trying to pass dev=NULL won't work, so that's why I'm enabling
parent clocks in platform driver probe.

I'm going to submit new patch series soon. It'll include all my recent
patches, addressing all your comments. We can continue discussion
there, in case I misunderstood you and those patches are still not
correct.

Thanks!

> --
> Regards,
> Sylwester