linux-kernel - Re: [PATCH v2 2/2] NFC: nxp-nci: Add pad supply voltage pvdd-supply

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Message-ID: <20230609173935.84424-1-raymondhackley@protonmail.com>
Date:   Fri, 09 Jun 2023 17:40:04 +0000
From:   Raymond Hackley <raymondhackley@...tonmail.com>
To:     krzysztof.kozlowski@...aro.org
Cc:     broonie@...nel.org, davem@...emloft.net,
        devicetree@...r.kernel.org, edumazet@...gle.com,
        jk@...econstruct.com.au, kuba@...nel.org, lgirdwood@...il.com,
        linux-kernel@...r.kernel.org, michael@...le.cc,
        netdev@...r.kernel.org, pabeni@...hat.com,
        raymondhackley@...tonmail.com, robh+dt@...nel.org,
        u.kleine-koenig@...gutronix.de
Subject: Re: [PATCH v2 2/2] NFC: nxp-nci: Add pad supply voltage pvdd-supply

Hi Krzysztof,

On Friday, June 9th, 2023 at 3:46 PM, Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:


> On 09/06/2023 17:42, Raymond Hackley wrote:
>
> > PN547/553, QN310/330 chips on some devices require a pad supply voltage
> > (PVDD). Otherwise, the NFC won't power up.
> >
> > Implement support for pad supply voltage pvdd-supply that is enabled by
> > the nxp-nci driver so that the regulator gets enabled when needed.
> >
> > Signed-off-by: Raymond Hackley raymondhackley@...tonmail.com
> > ---
> > drivers/nfc/nxp-nci/i2c.c | 42 +++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 42 insertions(+)
> >
> > diff --git a/drivers/nfc/nxp-nci/i2c.c b/drivers/nfc/nxp-nci/i2c.c
> > index d4c299be7949..1b8877757cee 100644
> > --- a/drivers/nfc/nxp-nci/i2c.c
> > +++ b/drivers/nfc/nxp-nci/i2c.c
> > @@ -35,6 +35,7 @@ struct nxp_nci_i2c_phy {
> >
> > struct gpio_desc *gpiod_en;
> > struct gpio_desc *gpiod_fw;
> > + struct regulator *pvdd;
> >
> > int hard_fault; /*
> > * < 0 if hardware error occurred (e.g. i2c err)
> > @@ -263,6 +264,22 @@ static const struct acpi_gpio_mapping acpi_nxp_nci_gpios[] = {
> > { }
> > };
> >
> > +static void nxp_nci_i2c_poweroff(void *data)
> > +{
> > + struct nxp_nci_i2c_phy *phy = data;
> > + struct device *dev = &phy->i2c_dev->dev;
> > + struct regulator *pvdd = phy->pvdd;
> > + int r;
> > +
> > + if (!IS_ERR(pvdd) && regulator_is_enabled(pvdd)) {
>
>
> Why do you need these checks? This should be called in correct context,
> so when regulator is valid and enabled. If you have such checks it
> suggests that code is buggy and this is being called in wrong contexts.
>

First condition !IS_ERR(pvdd) is to check if pvdd exists.
Some devices, msm8916-samsung-serranove for example, doesn't need pvdd or
have it bound in the device tree:

https://github.com/torvalds/linux/commit/ab0f0987e035f908d670fed7d86efa6fac66c0bb

Without !IS_ERR(pvdd), checking it with regulator_is_enabled(pvdd):

[   50.161882] 8<--- cut here ---
[   50.161906] Unable to handle kernel paging request at virtual address fffffff9 when read
[   50.161916] [fffffff9] *pgd=affff841, *pte=00000000, *ppte=00000000
[   50.161938] Internal error: Oops: 27 [#1] PREEMPT SMP ARM

Or disabling it directly with regulator_disable(pvdd):

[   69.439827] 8<--- cut here ---
[   69.439841] Unable to handle kernel NULL pointer dereference at virtual address 00000045 when read
[   69.439852] [00000045] *pgd=00000000
[   69.439864] Internal error: Oops: 5 [#1] PREEMPT SMP ARM

Second condition regulator_is_enabled(pvdd) is to make sure that pvdd is
disabled with balance.

Similar checks can be found here:

https://elixir.bootlin.com/linux/v6.4-rc5/source/drivers/staging/greybus/arche-apb-ctrl.c#L208

> > + r = regulator_disable(pvdd);
> > + if (r < 0)
> > + dev_warn(dev,
> > + "Failed to disable regulator pvdd: %d\n",
> > + r);
>
>
> Weird wrapping. Why r is wrapped?
>
> > + }
> > +}
> > +
> > static int nxp_nci_i2c_probe(struct i2c_client *client)
> > {
> > struct device *dev = &client->dev;
> > @@ -298,6 +315,29 @@ static int nxp_nci_i2c_probe(struct i2c_client *client)
> > return PTR_ERR(phy->gpiod_fw);
> > }
> >
> > + phy->pvdd = devm_regulator_get_optional(dev, "pvdd");
> > + if (IS_ERR(phy->pvdd)) {
> > + r = PTR_ERR(phy->pvdd);
> > + if (r != -ENODEV)
> > + return dev_err_probe(dev, r,
> > + "Failed to get regulator pvdd\n");
> > + } else {
> > + r = regulator_enable(phy->pvdd);
> > + if (r < 0) {
> > + nfc_err(dev,
> > + "Failed to enable regulator pvdd: %d\n",
> > + r);
>
>
> Weird wrapping. Why r is wrapped?
>
> > + return r;
> > + }
> > + }
> > +
> > + r = devm_add_action_or_reset(dev, nxp_nci_i2c_poweroff, phy);
> > + if (r < 0) {
> > + nfc_err(dev, "Failed to install poweroff handler: %d\n",
> > + r);
>
>
> Weird wrapping. Why r is wrapped?
>
> Just move it to the success path of enabling regulator.
>

Yes. This will be fixed in v3.

> > + return r;
> > + }
> > +
> > r = nxp_nci_probe(phy, &client->dev, &i2c_phy_ops,
> > NXP_NCI_I2C_MAX_PAYLOAD, &phy->ndev);
> > if (r < 0)
> > @@ -319,6 +359,8 @@ static void nxp_nci_i2c_remove(struct i2c_client *client)
> >
> > nxp_nci_remove(phy->ndev);
> > free_irq(client->irq, phy);
> > +
> > + nxp_nci_i2c_poweroff(phy);
>
>
> Why? This code is buggy...
>

I don't have a good reason to keep it and will drop it in v3.

Regards,
Raymond

>
>
> Best regards,
> Krzysztof