linux-kernel - Re: [PATCH] regulator: core: correct convergence check in regulator_set

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Message-ID: <e563ac87-ffb4-4272-b8bf-ef673a0952a4@nvidia.com>
Date: Tue, 29 Jul 2025 12:00:31 +0100
From: Jon Hunter <jonathanh@...dia.com>
To: Romain Gantois <romain.gantois@...tlin.com>,
 Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>
Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 linux-kernel@...r.kernel.org,
 "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH] regulator: core: correct convergence check in
 regulator_set_voltage()


On 29/07/2025 10:50, Romain Gantois wrote:
> The logic in regulator_set_voltage() which checks for a non-convergence
> condition on a stepped regulator is flawed.
> 
> regulator_set_voltage() checks if the error in target voltage has increased
> or decreased, and returns -EWOULDBLOCK if the error has not decreased
> enough. The correct non-convergence condition is:
> 
> new_delta - delta > -rdev->constraints->max_uV_step
> 
> or equivalently:
> 
> delta - new_delta < rdev->constraints->max_uV_step
> 
> But the currently used condition is:
> 
> new_delta - delta > rdev->constraints->max_uV_step
> 
> Which may cause an infinite loop if the voltage error doesn't converge.
> 
> Fix this by correcting the convergence condition.
> 
> Suggested-by: Jon Hunter <jonathanh@...dia.com>
> Fixes: d511206dc7443 ("regulator: core: repeat voltage setting request for stepped regulators")
> Signed-off-by: Romain Gantois <romain.gantois@...tlin.com>
> ---
>   drivers/regulator/core.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
> index 8ed9b96518cf5186c0db147a6895a92bc59fae4e..554d83c4af0c1c98edb43b60dbfacb8844d5e1eb 100644
> --- a/drivers/regulator/core.c
> +++ b/drivers/regulator/core.c
> @@ -3884,7 +3884,7 @@ static int regulator_set_voltage_unlocked(struct regulator *regulator,
>   			new_delta = ret;
>   
>   			/* check that voltage is converging quickly enough */
> -			if (new_delta - delta > rdev->constraints->max_uV_step) {
> +			if (delta - new_delta < rdev->constraints->max_uV_step) {
>   				ret = -EWOULDBLOCK;
>   				goto out;
>   			}


Thanks for the quick fix!

Tested-by: Jon Hunter <jonathanh@...dia.com>
Reviewed-by: Jon Hunter <jonathanh@...dia.com>

Jon

-- 
nvpublic