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

[Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxxxxx>]

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.

You know that as temporary solution you can add necessary clocks
directly in your DTS as fixed-rate-clocks? Effect would be quite similar
to the one here for UART driver but instead adding some temporary code
you would add temporary DTS nodes and references.

I am fine with this approach although the binding (if ever defined...)
would need to be marked as experimental.

> 
> 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" },
> +	{}
> +};
> +
> +static void __init exynos850_clk_init(struct device_node *np)
> +{
> +	void __iomem *reg_base;
> +	struct samsung_clk_provider *ctx;
> +
> +	reg_base = of_iomap(np, 0);
> +	if (!reg_base)
> +		panic("%s: failed to map registers\n", __func__);
> +
> +	ctx = samsung_clk_init(np, reg_base, CLK_NR_CLKS);
> +	if (!ctx)
> +		panic("%s: unable to allocate ctx\n", __func__);

Not needed, the samsung_clk_init() panics or returns valid memory.

> +
> +	samsung_clk_of_register_fixed_ext(ctx,
> +			exynos850_fixed_rate_ext_clks,
> +			ARRAY_SIZE(exynos850_fixed_rate_ext_clks),
> +			ext_clk_match);
> +
> +	samsung_clk_register_fixed_rate(ctx, exynos850_peri_clks,
> +			ARRAY_SIZE(exynos850_peri_clks));
> +
> +	samsung_clk_of_add_provider(np, ctx);
> +}
> +
> +CLK_OF_DECLARE(exynos850_clk, "samsung,exynos850-clock", exynos850_clk_init);
> 

Best regards,
Krzysztof