Re: [PATCH v2 7/8] clk: samsung: Add Exynos850 clock driver stub

[Sam Protsenko <semen.protsenko@xxxxxxxxxx>]

On Mon, 9 Aug 2021 at 14:23, Krzysztof Kozlowski
<krzysztof.kozlowski@xxxxxxxxxxxxx> wrote:
>
> On 06/08/2021 17:21, Sam Protsenko wrote:
> > For now it's just a stub driver to make the serial driver work. Later it
> > will be implemented properly. This driver doesn't really change clocks,
> > only registers the UART clock as a fixed-rate clock. Without this clock
> > driver the UART driver won't work, as it's trying to obtain "uart" clock
> > and fails if it's not able to.
> >
> > In order to get a functional serial console we have to implement that
> > minimal clock driver with "uart" clock. It's not necessary to actually
> > configure clocks, as those are already configured in bootloader, so
> > kernel can rely on that for now.
> >
> > Signed-off-by: Sam Protsenko <semen.protsenko@xxxxxxxxxx>
> > ---
> > Changes in v2:
> >   - Used hard coded clock indexes, as clock bindings were removed; will
> >     add clock bindings back (reimplemented) once proper clock driver is
> >     ready
> >   - Removed .data = 0 for exynos850-oscclk, as it's in BSS section
> >   - Removed comma for terminator {}
> >   - Made exynos850_clk_init() static
> >   - Removed checking np for NULL, as it's already done in of_iomap()
> >
> >  drivers/clk/samsung/Makefile        |  1 +
> >  drivers/clk/samsung/clk-exynos850.c | 64 +++++++++++++++++++++++++++++
> >  2 files changed, 65 insertions(+)
> >  create mode 100644 drivers/clk/samsung/clk-exynos850.c
> >
> > diff --git a/drivers/clk/samsung/Makefile b/drivers/clk/samsung/Makefile
> > index 028b2e27a37e..c46cf11e4d0b 100644
> > --- a/drivers/clk/samsung/Makefile
> > +++ b/drivers/clk/samsung/Makefile
> > @@ -17,6 +17,7 @@ obj-$(CONFIG_EXYNOS_ARM64_COMMON_CLK)       += clk-exynos5433.o
> >  obj-$(CONFIG_EXYNOS_AUDSS_CLK_CON) += clk-exynos-audss.o
> >  obj-$(CONFIG_EXYNOS_CLKOUT)  += clk-exynos-clkout.o
> >  obj-$(CONFIG_EXYNOS_ARM64_COMMON_CLK)        += clk-exynos7.o
> > +obj-$(CONFIG_EXYNOS_ARM64_COMMON_CLK)        += clk-exynos850.o
> >  obj-$(CONFIG_S3C2410_COMMON_CLK)+= clk-s3c2410.o
> >  obj-$(CONFIG_S3C2410_COMMON_DCLK)+= clk-s3c2410-dclk.o
> >  obj-$(CONFIG_S3C2412_COMMON_CLK)+= clk-s3c2412.o
> > diff --git a/drivers/clk/samsung/clk-exynos850.c b/drivers/clk/samsung/clk-exynos850.c
> > new file mode 100644
> > index 000000000000..36c7c7fe7cf0
> > --- /dev/null
> > +++ b/drivers/clk/samsung/clk-exynos850.c
> > @@ -0,0 +1,64 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Copyright (C) 2019 Samsung Electronics Co., Ltd.
> > + * Copyright (C) 2021 Linaro Ltd.
> > + *
> > + * Common Clock Framework support for Exynos850 SoC.
> > + */
> > +
> > +#include <linux/clk.h>
> > +#include <linux/clkdev.h>
> > +#include <linux/clk-provider.h>
> > +#include <linux/of.h>
> > +#include <linux/of_address.h>
> > +
> > +#include "clk.h"
> > +
> > +/* Will be extracted to bindings header once proper clk driver is implemented */
> > +#define OSCCLK               1
> > +#define DOUT_UART    2
> > +#define CLK_NR_CLKS  3
> > +
> > +/* Fixed rate clocks generated outside the SoC */
> > +static struct samsung_fixed_rate_clock exynos850_fixed_rate_ext_clks[] __initdata = {
> > +     FRATE(OSCCLK, "fin_pll", NULL, 0, 26000000),
> > +};
> > +
> > +/*
> > + * Model the UART clock as a fixed-rate clock for now, to make serial driver
> > + * work. This clock is already configured in the bootloader.
> > + */
> > +static const struct samsung_fixed_rate_clock exynos850_peri_clks[] __initconst = {
> > +     FRATE(DOUT_UART, "DOUT_UART", NULL, 0, 200000000),
> > +};
> > +
> > +static const struct of_device_id ext_clk_match[] __initconst = {
> > +     { .compatible = "samsung,exynos850-oscclk" },
>
> One more thing - I am not sure anymore if this is correct. AFAIR, we
> wanted to drop compatibles for external clocks.
>

I'll remove oscclk from the clock driver and device tree. It's not
needed right now anyway, as that driver is just a stub.

But I'd still like to know the proper way to define external clocks. I
can see that in exynos7.dtsi and exynos5433.dtsi there is just regular
fixed clock defined for "oscclk" (or "fin_pll"), and then that clock
is referenced in corresponding clock driver by its
'clock-output-names' property. I guess that approach is the
recommended one?

> Chanwoo, Sylwester, Tomasz,
> Do you remember the recommended approach? Shall it be like Exynos542x
> (samsung,exynos5420-oscclk) or Exynos5433?
>
>
> BTW, I am now converting some of existing clock controller bindings to
> dtschema.
>

I'll try to review those in a day, that might also be helpful when I
get to clk implementation. Btw, thank you for reviewing my patches in
such a quick pace!

> Best regards,
> Krzysztof