[PATCH 0/2] scpi: RfC - Allow to ignore invalid SCPI DVFS clock rates

[Neil Armstrong]

On 02/04/2017 10:03 PM, Heiner Kallweit wrote:
> On the Odroid C2 (Amlogic S905GXBB) the firmware defines SCPI DVFS cpu
> clock rates which make the system crash or at least unstable.
> Therefore cpufreq can't be used on this system as of today.
> Other systems might face similar issues with too optimistic SCPI SVFS
> clock rates.
> 
> This RfC patch series addresses this by allowing to define a max
> frequency per clock via DT. All frequencies for the respective clock
> exceeding this threshold will be ignored.
> 
> Heiner Kallweit (2):
>   clk: scpi: RfC - Allow to ignore invalid SCPI DVFS clock rates
>   cpufreq: scpi: RfC - Allow to ignore invalid SCPI DVFS clock rates
> 
>  Documentation/devicetree/bindings/arm/arm,scpi.txt |  7 +++++++
>  drivers/clk/clk-scpi.c                             | 15 ++++++++++++++-
>  drivers/cpufreq/scpi-cpufreq.c                     | 22 ++++++++++++++++++++++
>  3 files changed, 43 insertions(+), 1 deletion(-)
> 

Hi Heiner,

Thanks for this pathset, I have an alternative patchset for this feature.

My patchset adds a maximum frequency in the cpu node, this permits cleanly specifying
a max frequency per cluster and leave the SCPI code intact since it's only a protocol
implementation.

Please find below a simpler implementation only touching the scpi-cpufreq code.

Anyway, Sudeep, could you give us your point of view about such changes ?

Neil

----><--
diff --git a/Documentation/devicetree/bindings/arm/cpus.txt b/Documentation/devicetree/bindings/arm/cpus.txt
index a1bcfee..b813933 100644
--- a/Documentation/devicetree/bindings/arm/cpus.txt
+++ b/Documentation/devicetree/bindings/arm/cpus.txt
@@ -276,6 +276,14 @@ nodes to be present and contain the properties described below.

 			    where voltage is in uV, frequency is in MHz.

+	- arm,scpi-dvfs-max-freq
+		Usage: optional
+		Value type: <u32>
+		Definition:
+			Specifies the maximum DVFS frequency in Hz unit this
+			CPU can support when the OPP tables are obtained via
+			the SCP interface.
+
 Example 1 (dual-cluster big.LITTLE system 32-bit):

 	cpus {
diff --git a/arch/arm64/boot/dts/amlogic/meson-gxbb-odroidc2.dts b/arch/arm64/boot/dts/amlogic/meson-gxbb-odroidc2.dts
index 238fbea..881f20c 100644
--- a/arch/arm64/boot/dts/amlogic/meson-gxbb-odroidc2.dts
+++ b/arch/arm64/boot/dts/amlogic/meson-gxbb-odroidc2.dts
@@ -137,6 +137,22 @@
 	};
 };

+&cpu0 {
+	arm,scpi-dvfs-max-freq = <1536000000>;
+};
+
+&cpu1 {
+	arm,scpi-dvfs-max-freq = <1536000000>;
+};
+
+&cpu2 {
+	arm,scpi-dvfs-max-freq = <1536000000>;
+};
+
+&cpu3 {
+	arm,scpi-dvfs-max-freq = <1536000000>;
+};
+
 &uart_AO {
 	status = "okay";
 	pinctrl-0 = <&uart_ao_a_pins>;
diff --git a/drivers/cpufreq/scpi-cpufreq.c b/drivers/cpufreq/scpi-cpufreq.c
index ea7a4e1..80a6f27b 100644
--- a/drivers/cpufreq/scpi-cpufreq.c
+++ b/drivers/cpufreq/scpi-cpufreq.c
@@ -25,6 +25,7 @@
 #include <linux/pm_opp.h>
 #include <linux/scpi_protocol.h>
 #include <linux/types.h>
+#include <linux/of.h>

 #include "arm_big_little.h"

@@ -54,6 +55,11 @@ static int scpi_init_opp_table(const struct cpumask *cpumask)
 	struct scpi_opp *opp;
 	struct device *cpu_dev = get_cpu_device(cpumask_first(cpumask));
 	struct scpi_dvfs_info *info = scpi_get_dvfs_info(cpu_dev);
+	u32 max_freq = 0;
+
+	/* Eventually get a platform frequency limitation */
+	of_property_read_u32(cpu_dev->of_node, "arm,scpi-dvfs-max-freq",
+			     &max_freq);

 	if (IS_ERR(info))
 		return PTR_ERR(info);
@@ -62,6 +68,10 @@ static int scpi_init_opp_table(const struct cpumask *cpumask)
 		return -EIO;

 	for (opp = info->opps, idx = 0; idx < info->count; idx++, opp++) {
+		/* Drop unsupported frequencies */
+		if (max_freq && opp->freq > max_freq)
+			continue;
+
 		ret = dev_pm_opp_add(cpu_dev, opp->freq, opp->m_volt * 1000);
 		if (ret) {
 			dev_warn(cpu_dev, "failed to add opp %uHz %umV\n",