linux-kernel - Re: [PATCH v5] regulator: core: Resolve supply name earlier to prevent double-init

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Date:   Fri, 26 Aug 2022 07:55:13 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Christian Kohlschütter 
        <christian@...lschutter.com>, broonie@...nel.org
Cc:     heiko@...ech.de, lgirdwood@...il.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mmc@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        m.reichl@...etechno.de, robin.murphy@....com,
        vincent.legoll@...il.com, wens@...nel.org
Subject: Re: [PATCH v5] regulator: core: Resolve supply name earlier to
 prevent double-init

On 25.08.2022 23:28, Christian Kohlschütter wrote:
> Previously, an unresolved regulator supply reference upon calling
> regulator_register on an always-on or boot-on regulator caused
> set_machine_constraints to be called twice.
>
> This in turn may initialize the regulator twice, leading to voltage
> glitches that are timing-dependent. A simple, unrelated configuration
> change may be enough to hide this problem, only to be surfaced by
> chance.
>
> One such example is the SD-Card voltage regulator in a NanoPI R4S that
> would not initialize reliably unless the registration flow was just
> complex enough to allow the regulator to properly reset between calls.
>
> Fix this by re-arranging regulator_register, trying resolve the
> regulator's supply early enough that set_machine_constraints does not
> need to be called twice.
>
> Signed-off-by: Christian Kohlschütter <christian@...lschutter.com>

Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

> ---
>   drivers/regulator/core.c | 58 ++++++++++++++++++++++++----------------
>   1 file changed, 35 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
> index 77f60eef960..2ff0ab2730f 100644
> --- a/drivers/regulator/core.c
> +++ b/drivers/regulator/core.c
> @@ -5391,6 +5391,7 @@ regulator_register(const struct regulator_desc *regulator_desc,
>   	bool dangling_of_gpiod = false;
>   	struct device *dev;
>   	int ret, i;
> +	bool resolved_early = false;
>   
>   	if (cfg == NULL)
>   		return ERR_PTR(-EINVAL);
> @@ -5494,24 +5495,10 @@ regulator_register(const struct regulator_desc *regulator_desc,
>   	BLOCKING_INIT_NOTIFIER_HEAD(&rdev->notifier);
>   	INIT_DELAYED_WORK(&rdev->disable_work, regulator_disable_work);
>   
> -	/* preform any regulator specific init */
> -	if (init_data && init_data->regulator_init) {
> -		ret = init_data->regulator_init(rdev->reg_data);
> -		if (ret < 0)
> -			goto clean;
> -	}
> -
> -	if (config->ena_gpiod) {
> -		ret = regulator_ena_gpio_request(rdev, config);
> -		if (ret != 0) {
> -			rdev_err(rdev, "Failed to request enable GPIO: %pe\n",
> -				 ERR_PTR(ret));
> -			goto clean;
> -		}
> -		/* The regulator core took over the GPIO descriptor */
> -		dangling_cfg_gpiod = false;
> -		dangling_of_gpiod = false;
> -	}
> +	if (init_data && init_data->supply_regulator)
> +		rdev->supply_name = init_data->supply_regulator;
> +	else if (regulator_desc->supply_name)
> +		rdev->supply_name = regulator_desc->supply_name;
>   
>   	/* register with sysfs */
>   	rdev->dev.class = &regulator_class;
> @@ -5533,13 +5520,38 @@ regulator_register(const struct regulator_desc *regulator_desc,
>   		goto wash;
>   	}
>   
> -	if (init_data && init_data->supply_regulator)
> -		rdev->supply_name = init_data->supply_regulator;
> -	else if (regulator_desc->supply_name)
> -		rdev->supply_name = regulator_desc->supply_name;
> +	if ((rdev->supply_name && !rdev->supply) &&
> +		(rdev->constraints->always_on ||
> +		 rdev->constraints->boot_on)) {
> +		ret = regulator_resolve_supply(rdev);
> +		if (ret != 0)
> +			rdev_dbg(rdev, "Unable to resolve supply early: %pe\n",
> +				 ERR_PTR(ret));
> +
> +		resolved_early = true;
> +	}
> +
> +	/* perform any regulator specific init */
> +	if (init_data && init_data->regulator_init) {
> +		ret = init_data->regulator_init(rdev->reg_data);
> +		if (ret < 0)
> +			goto wash;
> +	}
> +
> +	if (config->ena_gpiod) {
> +		ret = regulator_ena_gpio_request(rdev, config);
> +		if (ret != 0) {
> +			rdev_err(rdev, "Failed to request enable GPIO: %pe\n",
> +					 ERR_PTR(ret));
> +			goto wash;
> +		}
> +		/* The regulator core took over the GPIO descriptor */
> +		dangling_cfg_gpiod = false;
> +		dangling_of_gpiod = false;
> +	}
>   
>   	ret = set_machine_constraints(rdev);
> -	if (ret == -EPROBE_DEFER) {
> +	if (ret == -EPROBE_DEFER && !resolved_early) {
>   		/* Regulator might be in bypass mode and so needs its supply
>   		 * to set the constraints
>   		 */

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland