Received-SPF: pass (google.com: domain of linux-kernel+bounces-88056-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Precedence: bulk
MIME-Version: 1.0
Date: Fri, 01 Mar 2024 09:13:34 +0100
From: Dragan Simic <dsimic@manjaro.org>
To: Alexey Charkov <alchark@gmail.com>
Cc: Rob Herring <robh+dt@kernel.org>, Krzysztof Kozlowski
 <krzysztof.kozlowski+dt@linaro.org>, Conor Dooley <conor+dt@kernel.org>,
 Heiko Stuebner <heiko@sntech.de>, Daniel Lezcano
 <daniel.lezcano@linaro.org>, Viresh Kumar <viresh.kumar@linaro.org>, Chen-Yu
 Tsai <wens@kernel.org>, devicetree@vger.kernel.org,
 linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org,
 linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 3/5] arm64: dts: rockchip: Add CPU/memory regulator
 coupling for RK3588
In-Reply-To: <20240229-rk-dts-additions-v3-3-6afe8473a631@gmail.com>
References: <20240229-rk-dts-additions-v3-0-6afe8473a631@gmail.com>
 <20240229-rk-dts-additions-v3-3-6afe8473a631@gmail.com>
Message-ID: <7e4379931dc6e35ca79a0ec7d27cf590@manjaro.org>
Content-Type: text/plain; charset=US-ASCII;
 format=flowed
Content-Transfer-Encoding: 7bit

On 2024-02-29 20:26, Alexey Charkov wrote:
> RK3588 chips allow for their CPU cores to be powered by a different
> supply vs. their corresponding memory interfaces, and two of the
> boards currently upstream do that (EVB1 and QuartzPro64).

The only reasonable explanation, based on the Cortex-A55 and Cortex-A76
technical reference manuals (TRMs), and some other documents, including
the RK3588 hardware design guide (HDG), is that the VDD_CPU_BIG0_MEM_S0,
VDD_CPU_BIG1_MEM_S0 and VDD_CPU_LIT_MEM_S0 voltages are internally
used as the supplies for the SRAM used for the A76's and A55's L1 and
L2 caches, which are both per-core and private in the DynamIQ SoC layout
that the RK3588 is based on.

Sure, using "MEM" there is confusing, but actually, the Cortex-A55 and
Cortex-A76 refer to the L1 and L2 caches as "memory" in multiple places.
I'd say that's the reason for "MEM" (and "memory", in the RK3588 HDG) to
be used in the board schematics (and in the RK3588 HDG).

The RK3588 HDG specifically allows what the Rock 5B does there, i.e. to
basically short the RK3588's individual *_MEM_S0 power inputs to the
respective CPU core power supplies, which avoids the need to use 
separate
voltage regulators for the RK3588's *_MEM_S0 power inputs.

However, I'd really, _really_ love to know why did Rockchip opt to make
the power supply voltages separate for the RK3588's L1 and L2 caches,
which are, BTW, rated for up to 100 mA for each *_MEM_S0 input, meaning
that they present no large loads?  All that under the assumption that
my analysis is correct, of course.

> The voltage of the memory interface though has to match that of the
> CPU cores that use it, which downstream kernels achieve by the means
> of a custom cpufreq driver which adjusts both at the same time.
> 
> It seems that regulator coupling is a more appropriate generic
> interface for it, so this patch introduces coupling to affected
> device trees to ensure that memory interface voltage is also updated
> whenever cpufreq switches between CPU OPPs.

I'll verify this a bit later and provide a separate response.

> Note that other boards, such as Radxa Rock 5B, define both the CPU
> and memory interface regulators as aliases to the same DT node, so
> this doesn't apply there.

Yup, they're actually shorted on the Rock 5B, as I described above.

> Signed-off-by: Alexey Charkov <alchark@gmail.com>
> ---
>  arch/arm64/boot/dts/rockchip/rk3588-evb1-v10.dts    | 12 ++++++++++++
>  arch/arm64/boot/dts/rockchip/rk3588-quartzpro64.dts | 12 ++++++++++++
>  2 files changed, 24 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/rockchip/rk3588-evb1-v10.dts
> b/arch/arm64/boot/dts/rockchip/rk3588-evb1-v10.dts
> index de30c2632b8e..dfae67f1e9c7 100644
> --- a/arch/arm64/boot/dts/rockchip/rk3588-evb1-v10.dts
> +++ b/arch/arm64/boot/dts/rockchip/rk3588-evb1-v10.dts
> @@ -788,6 +788,8 @@ regulators {
>  			vdd_cpu_big1_s0: dcdc-reg1 {
>  				regulator-always-on;
>  				regulator-boot-on;
> +				regulator-coupled-with = <&vdd_cpu_big1_mem_s0>;
> +				regulator-coupled-max-spread = <10000>;
>  				regulator-min-microvolt = <550000>;
>  				regulator-max-microvolt = <1050000>;
>  				regulator-ramp-delay = <12500>;
> @@ -800,6 +802,8 @@ regulator-state-mem {
>  			vdd_cpu_big0_s0: dcdc-reg2 {
>  				regulator-always-on;
>  				regulator-boot-on;
> +				regulator-coupled-with = <&vdd_cpu_big0_mem_s0>;
> +				regulator-coupled-max-spread = <10000>;
>  				regulator-min-microvolt = <550000>;
>  				regulator-max-microvolt = <1050000>;
>  				regulator-ramp-delay = <12500>;
> @@ -812,6 +816,8 @@ regulator-state-mem {
>  			vdd_cpu_lit_s0: dcdc-reg3 {
>  				regulator-always-on;
>  				regulator-boot-on;
> +				regulator-coupled-with = <&vdd_cpu_lit_mem_s0>;
> +				regulator-coupled-max-spread = <10000>;
>  				regulator-min-microvolt = <550000>;
>  				regulator-max-microvolt = <950000>;
>  				regulator-ramp-delay = <12500>;
> @@ -836,6 +842,8 @@ regulator-state-mem {
>  			vdd_cpu_big1_mem_s0: dcdc-reg5 {
>  				regulator-always-on;
>  				regulator-boot-on;
> +				regulator-coupled-with = <&vdd_cpu_big1_s0>;
> +				regulator-coupled-max-spread = <10000>;
>  				regulator-min-microvolt = <675000>;
>  				regulator-max-microvolt = <1050000>;
>  				regulator-ramp-delay = <12500>;
> @@ -849,6 +857,8 @@ regulator-state-mem {
>  			vdd_cpu_big0_mem_s0: dcdc-reg6 {
>  				regulator-always-on;
>  				regulator-boot-on;
> +				regulator-coupled-with = <&vdd_cpu_big0_s0>;
> +				regulator-coupled-max-spread = <10000>;
>  				regulator-min-microvolt = <675000>;
>  				regulator-max-microvolt = <1050000>;
>  				regulator-ramp-delay = <12500>;
> @@ -873,6 +883,8 @@ regulator-state-mem {
>  			vdd_cpu_lit_mem_s0: dcdc-reg8 {
>  				regulator-always-on;
>  				regulator-boot-on;
> +				regulator-coupled-with = <&vdd_cpu_lit_s0>;
> +				regulator-coupled-max-spread = <10000>;
>  				regulator-min-microvolt = <675000>;
>  				regulator-max-microvolt = <950000>;
>  				regulator-ramp-delay = <12500>;
> diff --git a/arch/arm64/boot/dts/rockchip/rk3588-quartzpro64.dts
> b/arch/arm64/boot/dts/rockchip/rk3588-quartzpro64.dts
> index 87a0abf95f7d..9c038450cd7c 100644
> --- a/arch/arm64/boot/dts/rockchip/rk3588-quartzpro64.dts
> +++ b/arch/arm64/boot/dts/rockchip/rk3588-quartzpro64.dts
> @@ -818,6 +818,8 @@ vdd_cpu_big1_s0: dcdc-reg1 {
>  				regulator-name = "vdd_cpu_big1_s0";
>  				regulator-always-on;
>  				regulator-boot-on;
> +				regulator-coupled-with = <&vdd_cpu_big1_mem_s0>;
> +				regulator-coupled-max-spread = <10000>;
>  				regulator-min-microvolt = <550000>;
>  				regulator-max-microvolt = <1050000>;
>  				regulator-ramp-delay = <12500>;
> @@ -831,6 +833,8 @@ vdd_cpu_big0_s0: dcdc-reg2 {
>  				regulator-name = "vdd_cpu_big0_s0";
>  				regulator-always-on;
>  				regulator-boot-on;
> +				regulator-coupled-with = <&vdd_cpu_big0_mem_s0>;
> +				regulator-coupled-max-spread = <10000>;
>  				regulator-min-microvolt = <550000>;
>  				regulator-max-microvolt = <1050000>;
>  				regulator-ramp-delay = <12500>;
> @@ -844,6 +848,8 @@ vdd_cpu_lit_s0: dcdc-reg3 {
>  				regulator-name = "vdd_cpu_lit_s0";
>  				regulator-always-on;
>  				regulator-boot-on;
> +				regulator-coupled-with = <&vdd_cpu_lit_mem_s0>;
> +				regulator-coupled-max-spread = <10000>;
>  				regulator-min-microvolt = <550000>;
>  				regulator-max-microvolt = <950000>;
>  				regulator-ramp-delay = <12500>;
> @@ -870,6 +876,8 @@ vdd_cpu_big1_mem_s0: dcdc-reg5 {
>  				regulator-name = "vdd_cpu_big1_mem_s0";
>  				regulator-always-on;
>  				regulator-boot-on;
> +				regulator-coupled-with = <&vdd_cpu_big1_s0>;
> +				regulator-coupled-max-spread = <10000>;
>  				regulator-min-microvolt = <675000>;
>  				regulator-max-microvolt = <1050000>;
>  				regulator-ramp-delay = <12500>;
> @@ -884,6 +892,8 @@ vdd_cpu_big0_mem_s0: dcdc-reg6 {
>  				regulator-name = "vdd_cpu_big0_mem_s0";
>  				regulator-always-on;
>  				regulator-boot-on;
> +				regulator-coupled-with = <&vdd_cpu_big0_s0>;
> +				regulator-coupled-max-spread = <10000>;
>  				regulator-min-microvolt = <675000>;
>  				regulator-max-microvolt = <1050000>;
>  				regulator-ramp-delay = <12500>;
> @@ -910,6 +920,8 @@ vdd_cpu_lit_mem_s0: dcdc-reg8 {
>  				regulator-name = "vdd_cpu_lit_mem_s0";
>  				regulator-always-on;
>  				regulator-boot-on;
> +				regulator-coupled-with = <&vdd_cpu_lit_s0>;
> +				regulator-coupled-max-spread = <10000>;
>  				regulator-min-microvolt = <675000>;
>  				regulator-max-microvolt = <950000>;
>  				regulator-ramp-delay = <12500>;