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

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Message-ID: <7ad5d027-9b15-f59e-aa76-17e498cb7aba@linaro.org>
Date:   Fri, 9 Jun 2023 21:29:51 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Raymond Hackley <raymondhackley@...tonmail.com>
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, robh+dt@...nel.org,
        u.kleine-koenig@...gutronix.de
Subject: Re: [PATCH v2 2/2] NFC: nxp-nci: Add pad supply voltage pvdd-supply

On 09/06/2023 19:40, Raymond Hackley wrote:
> 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:

If regulator is missing you should get a dummy.

But anyway the code will not be executed if you don't get proper regulator.

> 
> 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.
> 

So you have buggy code and to hide the bug you add checks? No, make the
code correct so the check is not needed.


> Similar checks can be found here:
> 
> https://elixir.bootlin.com/linux/v6.4-rc5/source/drivers/staging/greybus/arche-apb-ctrl.c#L208

staging driver is not an example...

> 


Best regards,
Krzysztof