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

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Message-ID: <3add6f87-7293-e1ae-8f9e-c69e9de18cf5@canonical.com>
Date:   Mon, 9 Aug 2021 13:22:56 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Sam Protsenko <semen.protsenko@...aro.org>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Tomasz Figa <tomasz.figa@...il.com>,
        Paweł Chmiel <pawel.mikolaj.chmiel@...il.com>
Cc:     Marc Zyngier <maz@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
        Ryu Euiyoul <ryu.real@...sung.com>,
        Tom Gall <tom.gall@...aro.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Amit Pundir <amit.pundir@...aro.org>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-clk@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH v2 7/8] clk: samsung: Add Exynos850 clock driver stub

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@...aro.org>
> ---
> 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.

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.

Best regards,
Krzysztof