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

[Matthias Brugger <matthias.bgg@gmail.com>]

On 10/01/2024 15:23, Nícolas F. R. A. Prado wrote:
> 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>

Reviewed-by: Matthias Brugger <matthias.bgg@gmail.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)