[PATCH v2 2/2] cpufreq: mediatek-hw: Wait for CPU supplies before probing

["Nícolas F. R. A. Prado" <nfraprado@collabora.com>]

Before proceeding with the probe and enabling frequency scaling for the
CPUs, make sure that all supplies feeding the CPUs have probed.

This fixes an issue observed on MT8195-Tomato where if the
mediatek-cpufreq-hw driver enabled the hardware (by writing to
REG_FREQ_ENABLE) before the SPMI controller driver (spmi-mtk-pmif),
behind which lies the big CPU supply, probed the platform would hang
shortly after with "rcu: INFO: rcu_preempt detected stalls on
CPUs/tasks" being printed in the log.

Fixes: 4855e26bcf4d ("cpufreq: mediatek-hw: Add support for CPUFREQ HW")
Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>

---

Changes in v2:
- Added this commit

 drivers/cpufreq/mediatek-cpufreq-hw.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/mediatek-cpufreq-hw.c b/drivers/cpufreq/mediatek-cpufreq-hw.c
index d46afb3c0092..a1aa9385980a 100644
--- a/drivers/cpufreq/mediatek-cpufreq-hw.c
+++ b/drivers/cpufreq/mediatek-cpufreq-hw.c
@@ -13,6 +13,7 @@
 #include <linux/of.h>
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
+#include <linux/regulator/consumer.h>
 #include <linux/slab.h>
 
 #define LUT_MAX_ENTRIES			32U
@@ -300,7 +301,23 @@ static struct cpufreq_driver cpufreq_mtk_hw_driver = {
 static int mtk_cpufreq_hw_driver_probe(struct platform_device *pdev)
 {
 	const void *data;
-	int ret;
+	int ret, cpu;
+	struct device *cpu_dev;
+	struct regulator *cpu_reg;
+
+	/* Make sure that all CPU supplies are available before proceeding. */
+	for_each_possible_cpu(cpu) {
+		cpu_dev = get_cpu_device(cpu);
+		if (!cpu_dev)
+			return dev_err_probe(&pdev->dev, -EPROBE_DEFER,
+					     "Failed to get cpu%d device\n", cpu);
+
+		cpu_reg = devm_regulator_get_optional(cpu_dev, "cpu");
+		if (IS_ERR(cpu_reg))
+			return dev_err_probe(&pdev->dev, PTR_ERR(cpu_reg),
+					     "CPU%d regulator get failed\n", cpu);
+	}
+
 
 	data = of_device_get_match_data(&pdev->dev);
 	if (!data)
-- 
2.43.0