Re: [PATCH] soc/tegra: regulators: Fix locking up when voltage-spread is out of range in tegra20

[Mikko Perttunen <mperttunen@nvidia.com>]

On Saturday, September 6, 2025 7:50 PM Chen Yufeng wrote:
> This patch is similar to ef85bb582c41("soc/tegra: regulators: Fix
>  locking up when voltage-spread is out of range").
> 
> A potential deadlock issue exists in the voltage coupler code for 
> Tegra20 when the voltage spread (voltage-spread) goes out of range.
> The code does not properly account for the maximum voltage spread 
> (max-spread) requirement when the CPU regulator has no consumers.
> 
> In the tegra20_cpu_voltage_update function, the voltage range is 
> not properly handled when there are no consumers:
> ```c
> if (!cpu_min_uV_consumers)
>     cpu_min_uV = cpu_uV;
> ```
> When there are no CPU consumers, cpu_min_uV is directly set to cpu_uV, 
> without considering the maximum voltage spread constraint.
> 
> The issue is resolved by introducing the max function to ensure that 
> cpu_min_uV is set to the greater value between cpu_uV and cpu_min_uV, 
> thereby preventing the voltage spread from exceeding the limit:
> ```c
> if (!cpu_min_uV_consumers)
>     cpu_min_uV = max(cpu_uV, cpu_min_uV);
> ```

I don't think this applies to this driver. If cpu_min_uV == cpu_uV, no voltage change will occur, hence the voltage spread will not change.

Thanks,
Mikko

> 
> Signed-off-by: Chen Yufeng <chenyufeng@iie.ac.cn>
> ---
>  drivers/soc/tegra/regulators-tegra20.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/soc/tegra/regulators-tegra20.c b/drivers/soc/tegra/regulators-tegra20.c
> index 6a2f90ab9d3e..48c29b89fa59 100644
> --- a/drivers/soc/tegra/regulators-tegra20.c
> +++ b/drivers/soc/tegra/regulators-tegra20.c
> @@ -305,7 +305,7 @@ static int tegra20_cpu_voltage_update(struct tegra_regulator_coupler *tegra,
>  	 * survive the voltage drop if it's running on a higher frequency.
>  	 */
>  	if (!cpu_min_uV_consumers)
> -		cpu_min_uV = cpu_uV;
> +		cpu_min_uV = max(cpu_uV, cpu_min_uV);
>  
>  	/* restore boot voltage level */
>  	if (tegra->sys_reboot_mode)
>