Re: [PATCH v4] soc: samsung: Add simple voltage coupler for Exynos5800

[Krzysztof Kozlowski <krzk@kernel.org>]

On Mon, Jun 15, 2020 at 12:43:15PM +0200, Marek Szyprowski wrote:
> Add a simple custom voltage regulator coupler for Exynos5800 SoCs, which
> require coupling between "vdd_arm" and "vdd_int" regulators. This coupler
> ensures that the voltage values don't go below the bootloader-selected
> operation point during the boot process until a the clients sets their
> constraints. It is achieved by assuming minimal voltage value equal to
> the current value if no constraints are set. This also ensures proper
> voltage balancing if any of the client driver is missing.
> 
> The balancing code comes from the regulator/core.c with the additional
> logic for handling regulators without client constraints applied added.
> 
> Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
> This patch is yet another attempt to fix the regulator coupling on
> Exynos5800/5422 SoCs. Here are links to the previous attempts and
> discussions:
> 
> https://lore.kernel.org/linux-samsung-soc/20191008101709.qVNy8eijBi0LynOteWFMnTg4GUwKG599n6OyYoX1Abs@z/
> https://lore.kernel.org/lkml/20191017102758.8104-1-m.szyprowski@samsung.com/
> https://lore.kernel.org/linux-pm/cover.1589528491.git.viresh.kumar@linaro.org/
> https://lore.kernel.org/linux-pm/20200528131130.17984-1-m.szyprowski@samsung.com/
> https://lore.kernel.org/linux-samsung-soc/57cf3a15-5d9b-7636-4c69-60742e8cfae6@samsung.com/
> https://lore.kernel.org/lkml/20200605063724.9030-1-m.szyprowski@samsung.com/
> 
> The problem is with "vdd_int" regulator coupled with "vdd_arm" on Odroid
> XU3/XU4 boards family. "vdd_arm" is handled by CPUfreq. "vdd_int" is
> handled by devfreq. CPUfreq initialized quite early during boot and it
> starts changing OPPs and "vdd_arm" value. Sometimes CPU activity during
> boot goes down and some low-frequency OPPs are selected, what in turn
> causes lowering "vdd_arm". This happens before devfreq applies its
> requirements on "vdd_int". Regulator balancing code reduces "vdd_arm"
> voltage value, what in turn causes lowering "vdd_int" value to the lowest
> possible value. This is much below the operation point of the wcore bus,
> which still runs at the highest frequency.
> 
> The issue was hard to notice because in the most cases the board managed
> to boot properly, even when the regulator was set to lowest value allowed
> by the regulator constraints. However, it caused some random issues,
> which can be observed as "Unhandled prefetch abort" or low USB stability.
> 
> Handling this case in the generic code has been rejected, so the only way
> to ensure the desired behavior on Exynos5800-based SoCs is to make a
> custom regulator coupler driver. I've tried hard to extract some common
> code to simplify the exynos-regulator-coupler driver as much as possible,
> but the difference between it and the generic code is so deep that this
> approach failed, so indead I simply copied and modified the balancing
> code.
> 
> Best regards
> Marek Szyprowski
> ---
>  arch/arm/mach-exynos/Kconfig                  |   1 +
>  drivers/soc/samsung/Kconfig                   |   3 +
>  drivers/soc/samsung/Makefile                  |   1 +
>  .../soc/samsung/exynos-regulator-coupler.c    | 221 ++++++++++++++++++
>  4 files changed, 226 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 19c4d3f1437b..5d7819b52eed 100644
> --- a/drivers/soc/samsung/Kconfig
> +++ b/drivers/soc/samsung/Kconfig
> @@ -43,4 +43,7 @@ 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 31db65cb7aa3..93285faec416 100644
> --- a/drivers/soc/samsung/Makefile
> +++ b/drivers/soc/samsung/Makefile
> @@ -10,3 +10,4 @@ obj-$(CONFIG_EXYNOS_PMU_ARM_DRIVERS)	+= exynos3250-pmu.o exynos4-pmu.o \
>  					exynos5250-pmu.o exynos5420-pmu.o
>  obj-$(CONFIG_EXYNOS_PMU_ARM64_DRIVERS)	+= exynos-pm.o exynos5433-pmu.o

You based this patch on some different tree. Does not apply.

Best regards,
Krzysztof

>  obj-$(CONFIG_EXYNOS_PM_DOMAINS) += pm_domains.o
> +obj-$(CONFIG_EXYNOS_REGULATOR_COUPLER) += exynos-regulator-coupler.o