Re: [PATCH 2/2] soc: samsung: Add simple voltage coupler for Exynos5800

[Krzysztof Kozlowski <krzk@xxxxxxxxxx>]

On Fri, May 29, 2020 at 02:49:40PM +0200, Marek Szyprowski wrote:
> Add custom voltage regulator coupler for Exynos5800 SoCs, which require
> coupling between "vdd_arm" and "vdd_int" regulators. This coupler ensures
> that coupled regulators voltage balancing is done only when clients for
> each regulator (cpufreq for "vdd_arm" and devfreq for "vdd_int") apply
> their constraints, so the voltage values don't go beyond the
> bootloader-selected operation point during the boot process. This also
> ensures proper voltage balancing if any of those drivers is missing.
> 
> Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> ---
>  arch/arm/mach-exynos/Kconfig                  |  1 +
>  drivers/soc/samsung/Kconfig                   |  3 +
>  drivers/soc/samsung/Makefile                  |  1 +
>  .../soc/samsung/exynos-regulator-coupler.c    | 59 +++++++++++++++++++
>  4 files changed, 64 insertions(+)
>  create mode 100644 drivers/soc/samsung/exynos-regulator-coupler.c
> 
> diff --git a/arch/arm/mach-exynos/Kconfig b/arch/arm/mach-exynos/Kconfig
> index 76838255b5fa..f185cd3d4c62 100644
> --- a/arch/arm/mach-exynos/Kconfig
> +++ b/arch/arm/mach-exynos/Kconfig
> @@ -118,6 +118,7 @@ config SOC_EXYNOS5800
>  	bool "Samsung EXYNOS5800"
>  	default y
>  	depends on SOC_EXYNOS5420
> +	select EXYNOS_REGULATOR_COUPLER
>  
>  config EXYNOS_MCPM
>  	bool
> diff --git a/drivers/soc/samsung/Kconfig b/drivers/soc/samsung/Kconfig
> index c7a2003687c7..264185664594 100644
> --- a/drivers/soc/samsung/Kconfig
> +++ b/drivers/soc/samsung/Kconfig
> @@ -37,4 +37,7 @@ config EXYNOS_PM_DOMAINS
>  	bool "Exynos PM domains" if COMPILE_TEST
>  	depends on PM_GENERIC_DOMAINS || COMPILE_TEST
>  
> +config EXYNOS_REGULATOR_COUPLER
> +	bool "Exynos SoC Regulator Coupler" if COMPILE_TEST
> +	depends on ARCH_EXYNOS || COMPILE_TEST
>  endif
> diff --git a/drivers/soc/samsung/Makefile b/drivers/soc/samsung/Makefile
> index edd1d6ea064d..ecc3a32f6406 100644
> --- a/drivers/soc/samsung/Makefile
> +++ b/drivers/soc/samsung/Makefile
> @@ -9,3 +9,4 @@ obj-$(CONFIG_EXYNOS_PMU)	+= exynos-pmu.o
>  obj-$(CONFIG_EXYNOS_PMU_ARM_DRIVERS)	+= exynos3250-pmu.o exynos4-pmu.o \
>  					exynos5250-pmu.o exynos5420-pmu.o
>  obj-$(CONFIG_EXYNOS_PM_DOMAINS) += pm_domains.o
> +obj-$(CONFIG_EXYNOS_REGULATOR_COUPLER) += exynos-regulator-coupler.o
> diff --git a/drivers/soc/samsung/exynos-regulator-coupler.c b/drivers/soc/samsung/exynos-regulator-coupler.c
> new file mode 100644
> index 000000000000..54445918bd75
> --- /dev/null
> +++ b/drivers/soc/samsung/exynos-regulator-coupler.c
> @@ -0,0 +1,59 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2020 Samsung Electronics Co., Ltd.
> + *	      http://www.samsung.com/
> + * Author: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> + *
> + * Samsung Exynos SoC voltage coupler
> + */
> +
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/of.h>
> +#include <linux/regulator/coupler.h>
> +#include <linux/regulator/driver.h>
> +
> +static int exynos_coupler_balance_voltage(struct regulator_coupler *coupler,
> +					  struct regulator_dev *rdev,
> +					  suspend_state_t state)
> +{
> +	struct coupling_desc *c_desc = &rdev->coupling_desc;
> +	int ret, cons_uV = 0, cons_max_uV = INT_MAX;
> +	bool skip_coupled = false;
> +
> +	/* get coupled regulator constraints */
> +	ret = regulator_check_consumers(c_desc->coupled_rdevs[1], &cons_uV,
> +					&cons_max_uV, state);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* skip adjusting coupled regulator if it has no constraints set yet */
> +	if (cons_uV == 0)
> +		skip_coupled = true;
> +
> +	return regulator_do_balance_voltage(rdev, state, skip_coupled);
> +}
> +
> +static int exynos_coupler_attach(struct regulator_coupler *coupler,
> +				 struct regulator_dev *rdev)
> +{
> +	if (strcmp(rdev_get_name(rdev), "vdd_arm") == 0 ||
> +	    strcmp(rdev_get_name(rdev), "vdd_int") == 0)

Thanks for the patch!

You hard-coded specific names of regulators existing
only in DTS. They do not come from any driver nor bindings, therefore
they could change making driver unusable. Someone could add a new DTS
with different names and expect this to work as well.

You need bindings for this. Something like:
Documentation/devicetree/bindings/regulator/nvidia,tegra-regulators-coupling.txt
But better in YAML, if possible.

Best regards,
Krzysztof