[PATCH] regulator: core: Resolve supply name earlier to prevent double-init

[PATCH] regulator: core: Resolve supply name earlier to prevent double-init

[Christian Kohlschütter]

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@kohlschutter.com>
---
 drivers/regulator/core.c | 42 ++++++++++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 14 deletions(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index c4d844ffad7a..728840827e9c 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -5433,7 +5433,34 @@ 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 */
+	/* set regulator constraints */
+	if (init_data)
+		rdev->constraints = kmemdup(&init_data->constraints,
+					    sizeof(*rdev->constraints),
+					    GFP_KERNEL);
+	else
+		rdev->constraints = kzalloc(sizeof(*rdev->constraints),
+					    GFP_KERNEL);
+
+	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
+		&& (rdev->constraints->always_on || rdev->constraints->boot_on)) {
+		/* Try to resolve the name of the supplying regulator here first
+		 * so we prevent double-initializing the regulator, which may
+		 * cause timing-specific voltage brownouts/glitches that are
+		 * hard to debug.
+		 */
+		ret = regulator_resolve_supply(rdev);
+		if (ret)
+			rdev_dbg(rdev, "unable to resolve supply early: %pe\n",
+					 ERR_PTR(ret));
+	}
+
+	/* perform any regulator specific init */
 	if (init_data && init_data->regulator_init) {
 		ret = init_data->regulator_init(rdev->reg_data);
 		if (ret < 0)
@@ -5459,24 +5486,11 @@ regulator_register(const struct regulator_desc *regulator_desc,
 		    (unsigned long) atomic_inc_return(&regulator_no));
 	dev_set_drvdata(&rdev->dev, rdev);
 
-	/* set regulator constraints */
-	if (init_data)
-		rdev->constraints = kmemdup(&init_data->constraints,
-					    sizeof(*rdev->constraints),
-					    GFP_KERNEL);
-	else
-		rdev->constraints = kzalloc(sizeof(*rdev->constraints),
-					    GFP_KERNEL);
 	if (!rdev->constraints) {
 		ret = -ENOMEM;
 		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;
-
 	ret = set_machine_constraints(rdev);
 	if (ret == -EPROBE_DEFER) {
 		/* Regulator might be in bypass mode and so needs its supply
-- 
2.36.1

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

[Christian Kohlschütter]

Hi all,

This is a follow-up patch from my patch on mmc side:
[PATCH v4] arm64: dts: rockchip: Fix SD card init on rk3399-nanopi4
https://patchwork.kernel.org/project/linux-rockchip/patch/73F9AED0-D2A8-4294-B6E1-1B92D2A36529@kohlschutter.com/

Thanks to Robin Murphy's help, we were able to figure out that my NanoPI R4S's SD-Card voltage regulator was initialized twice and that a voltage drop was the reason for the initialization failure.
Adding an mdelay to the init code, or — surprisingly — adding a "regulator-uv-protection-microvolt" declaration had "fixed" the issue in 99/100 tries.

Best,
Christian

from arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi:
vcc3v0_sd: vcc3v0-sd {
        compatible = "regulator-fixed";
        enable-active-high;
        gpio = <&gpio0 RK_PA1 GPIO_ACTIVE_HIGH>;
        pinctrl-names = "default";
        pinctrl-0 = <&sdmmc0_pwr_h>;
        regulator-always-on;
        regulator-min-microvolt = <3000000>;
        regulator-max-microvolt = <3000000>;
        regulator-name = "vcc3v0_sd";
        vin-supply = <&vcc3v3_sys>;
};                                        

> Am 15.07.2022 um 22:32 schrieb Christian Kohlschütter <christian@kohlschutter.com>:
> 
> 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@kohlschutter.com>
> ---
> drivers/regulator/core.c | 42 ++++++++++++++++++++++++++--------------
> 1 file changed, 28 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
> index c4d844ffad7a..728840827e9c 100644
> --- a/drivers/regulator/core.c
> +++ b/drivers/regulator/core.c
> @@ -5433,7 +5433,34 @@ 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 */
> +	/* set regulator constraints */
> +	if (init_data)
> +		rdev->constraints = kmemdup(&init_data->constraints,
> +					    sizeof(*rdev->constraints),
> +					    GFP_KERNEL);
> +	else
> +		rdev->constraints = kzalloc(sizeof(*rdev->constraints),
> +					    GFP_KERNEL);
> +
> +	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
> +		&& (rdev->constraints->always_on || rdev->constraints->boot_on)) {
> +		/* Try to resolve the name of the supplying regulator here first
> +		 * so we prevent double-initializing the regulator, which may
> +		 * cause timing-specific voltage brownouts/glitches that are
> +		 * hard to debug.
> +		 */
> +		ret = regulator_resolve_supply(rdev);
> +		if (ret)
> +			rdev_dbg(rdev, "unable to resolve supply early: %pe\n",
> +					 ERR_PTR(ret));
> +	}
> +
> +	/* perform any regulator specific init */
> 	if (init_data && init_data->regulator_init) {
> 		ret = init_data->regulator_init(rdev->reg_data);
> 		if (ret < 0)
> @@ -5459,24 +5486,11 @@ regulator_register(const struct regulator_desc *regulator_desc,
> 		    (unsigned long) atomic_inc_return(&regulator_no));
> 	dev_set_drvdata(&rdev->dev, rdev);
> 
> -	/* set regulator constraints */
> -	if (init_data)
> -		rdev->constraints = kmemdup(&init_data->constraints,
> -					    sizeof(*rdev->constraints),
> -					    GFP_KERNEL);
> -	else
> -		rdev->constraints = kzalloc(sizeof(*rdev->constraints),
> -					    GFP_KERNEL);
> 	if (!rdev->constraints) {
> 		ret = -ENOMEM;
> 		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;
> -
> 	ret = set_machine_constraints(rdev);
> 	if (ret == -EPROBE_DEFER) {
> 		/* Regulator might be in bypass mode and so needs its supply
> -- 
> 2.36.1
> 

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

[Mark Brown]

[-- Attachment #1: Type: text/plain, Size: 990 bytes --]

On Fri, Jul 15, 2022 at 10:32:16PM +0200, 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.

One small thing below but otherwise I think this should be fine, however
since we're very near the merge window I'd rather hold off any apply at
-rc1, just to give more time for things to get tested.

> -	/* set regulator constraints */
> -	if (init_data)
> -		rdev->constraints = kmemdup(&init_data->constraints,
> -					    sizeof(*rdev->constraints),
> -					    GFP_KERNEL);
> -	else
> -		rdev->constraints = kzalloc(sizeof(*rdev->constraints),
> -					    GFP_KERNEL);
>  	if (!rdev->constraints) {
>  		ret = -ENOMEM;
>  		goto wash;
>  	}

The check for allocation failure should get pulled earlier in the
function along with the allocation, no sense in doing any of the other
work if we're going to fail.

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

[PATCH v2] regulator: core: Resolve supply name earlier to prevent double-init

[Christian Kohlschütter]

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@kohlschutter.com>
---
 drivers/regulator/core.c | 51 +++++++++++++++++++++++++---------------
 1 file changed, 32 insertions(+), 19 deletions(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 398c8d6afd4..5c2b97ea633 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -5492,7 +5492,38 @@ 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 */
+	/* set regulator constraints */
+	if (init_data)
+		rdev->constraints = kmemdup(&init_data->constraints,
+					    sizeof(*rdev->constraints),
+					    GFP_KERNEL);
+	else
+		rdev->constraints = kzalloc(sizeof(*rdev->constraints),
+					    GFP_KERNEL);
+	if (!rdev->constraints) {
+		ret = -ENOMEM;
+		goto clean;
+	}
+
+	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
+		&& (rdev->constraints->always_on || rdev->constraints->boot_on)) {
+		/* Try to resolve the name of the supplying regulator here first
+		 * so we prevent double-initializing the regulator, which may
+		 * cause timing-specific voltage brownouts/glitches that are
+		 * hard to debug.
+		 */
+		ret = regulator_resolve_supply(rdev);
+		if (ret)
+			rdev_dbg(rdev, "unable to resolve supply early: %pe\n",
+					 ERR_PTR(ret));
+	}
+
+	/* perform any regulator specific init */
 	if (init_data && init_data->regulator_init) {
 		ret = init_data->regulator_init(rdev->reg_data);
 		if (ret < 0)
@@ -5518,24 +5549,6 @@ regulator_register(const struct regulator_desc *regulator_desc,
 		    (unsigned long) atomic_inc_return(&regulator_no));
 	dev_set_drvdata(&rdev->dev, rdev);
 
-	/* set regulator constraints */
-	if (init_data)
-		rdev->constraints = kmemdup(&init_data->constraints,
-					    sizeof(*rdev->constraints),
-					    GFP_KERNEL);
-	else
-		rdev->constraints = kzalloc(sizeof(*rdev->constraints),
-					    GFP_KERNEL);
-	if (!rdev->constraints) {
-		ret = -ENOMEM;
-		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;
-
 	ret = set_machine_constraints(rdev);
 	if (ret == -EPROBE_DEFER) {
 		/* Regulator might be in bypass mode and so needs its supply
-- 
2.36.2

Re: [PATCH v2] regulator: core: Resolve supply name earlier to prevent double-init

[Christian Kohlschütter]

> On 18. Aug 2022, at 17:22, Mark Brown <broonie@kernel.org> wrote:
> 
> On Fri, 22 Jul 2022 19:42:27 +0200, 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.
>> 
>> [...]
> 
> Applied to
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator.git for-next
> 
> Thanks!
> 
> [1/1] regulator: core: Resolve supply name earlier to prevent double-init
>    commit: 8a866d527ac0441c0eb14a991fa11358b476b11d
> 
> All being well this means that it will be integrated into the linux-next
> tree (usually sometime in the next 24 hours) and sent to Linus during
> the next merge window (or sooner if it is a bug fix), however if
> problems are discovered then the patch may be dropped or reverted.
> 
> You may get further e-mails resulting from automated or manual testing
> and review of the tree, please engage with people reporting problems and
> send followup patches addressing any issues that are reported if needed.
> 
> If any updates are required or you are submitting further changes they
> should be sent as incremental updates against current git, existing
> patches will not be replaced.
> 
> Please add any relevant lists and maintainers to the CCs when replying
> to this mail.
> 
> Thanks,
> Mark

I've finally managed to publish a blog post about this journey into regulator land; I hope you find it worthwhile.
https://kohlschuetter.github.io/blog/posts/2022/10/28/linux-nanopi-r4s/

Thanks to everybody involved for getting this far!
Special thanks go to Robin Murphy for pulling out the oscillator, and Mark Brown for helping that these changes get into 6.1.

Best,
Christian