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Subject: Re: [PATCH] regulator: core: Resolve supply name earlier to prevent
 double-init
From:   =?utf-8?Q?Christian_Kohlsch=C3=BCtter?= 
        <christian@kohlschutter.com>
In-Reply-To: <3B4AE882-0C28-41E3-9466-F8E301567627@kohlschutter.com>
Date:   Fri, 15 Jul 2022 22:51:52 +0200
Cc:     Robin Murphy <robin.murphy@arm.com>, wens@kernel.org,
        =?utf-8?Q?Heiko_St=C3=BCbner?= <heiko@sntech.de>,
        Markus Reichl <m.reichl@fivetechno.de>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@lists.infradead.org>,
        Linux MMC List <linux-mmc@vger.kernel.org>
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Message-Id: <DFF60E71-B8CF-43C9-B476-9216AFF0463B@kohlschutter.com>
References: <3B4AE882-0C28-41E3-9466-F8E301567627@kohlschutter.com>
To:     Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Precedence: bulk

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-D2A8-42=
94-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 =E2=80=94 surprisingly =E2=80=94 =
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 =3D "regulator-fixed";
        enable-active-high;
        gpio =3D <&gpio0 RK_PA1 GPIO_ACTIVE_HIGH>;
        pinctrl-names =3D "default";
        pinctrl-0 =3D <&sdmmc0_pwr_h>;
        regulator-always-on;
        regulator-min-microvolt =3D <3000000>;
        regulator-max-microvolt =3D <3000000>;
        regulator-name =3D "vcc3v0_sd";
        vin-supply =3D <&vcc3v3_sys>;
};                                       =20

> Am 15.07.2022 um 22:32 schrieb Christian Kohlsch=C3=BCtter =
<christian@kohlschutter.com>:
>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> Signed-off-by: Christian Kohlsch=C3=BCtter =
<christian@kohlschutter.com>
> ---
> drivers/regulator/core.c | 42 ++++++++++++++++++++++++++--------------
> 1 file changed, 28 insertions(+), 14 deletions(-)
>=20
> 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);
>=20
> -	/* preform any regulator specific init */
> +	/* set regulator constraints */
> +	if (init_data)
> +		rdev->constraints =3D kmemdup(&init_data->constraints,
> +					    sizeof(*rdev->constraints),
> +					    GFP_KERNEL);
> +	else
> +		rdev->constraints =3D =
kzalloc(sizeof(*rdev->constraints),
> +					    GFP_KERNEL);
> +
> +	if (init_data && init_data->supply_regulator)
> +		rdev->supply_name =3D init_data->supply_regulator;
> +	else if (regulator_desc->supply_name)
> +		rdev->supply_name =3D 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 =3D 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 =3D 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);
>=20
> -	/* set regulator constraints */
> -	if (init_data)
> -		rdev->constraints =3D kmemdup(&init_data->constraints,
> -					    sizeof(*rdev->constraints),
> -					    GFP_KERNEL);
> -	else
> -		rdev->constraints =3D =
kzalloc(sizeof(*rdev->constraints),
> -					    GFP_KERNEL);
> 	if (!rdev->constraints) {
> 		ret =3D -ENOMEM;
> 		goto wash;
> 	}
>=20
> -	if (init_data && init_data->supply_regulator)
> -		rdev->supply_name =3D init_data->supply_regulator;
> -	else if (regulator_desc->supply_name)
> -		rdev->supply_name =3D regulator_desc->supply_name;
> -
> 	ret =3D set_machine_constraints(rdev);
> 	if (ret =3D=3D -EPROBE_DEFER) {
> 		/* Regulator might be in bypass mode and so needs its =
supply
> --=20
> 2.36.1
>=20