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Date:   Fri, 09 Jun 2023 20:44:00 +0000
To:     krzysztof.kozlowski@linaro.org
From:   Raymond Hackley <raymondhackley@protonmail.com>
Cc:     broonie@kernel.org, davem@davemloft.net,
        devicetree@vger.kernel.org, edumazet@google.com,
        jk@codeconstruct.com.au, kuba@kernel.org, lgirdwood@gmail.com,
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        netdev@vger.kernel.org, pabeni@redhat.com,
        raymondhackley@protonmail.com, robh+dt@kernel.org,
        u.kleine-koenig@pengutronix.de
Subject: Re: [PATCH v2 2/2] NFC: nxp-nci: Add pad supply voltage pvdd-supply
Message-ID: <20230609204329.105189-1-raymondhackley@protonmail.com>
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Hi Krzysztof,

On Friday, June 9th, 2023 at 7:29 PM, Krzysztof Kozlowski <krzysztof.kozlow=
ski@linaro.org> wrote:

> > > Why do you need these checks? This should be called in correct contex=
t,
> > > 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 context=
s.
> >=20
> > 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:
>=20
>=20
> If regulator is missing you should get a dummy.
>=20
> But anyway the code will not be executed if you don't get proper regulato=
r.
>=20

The current patch set is using devm_regulator_get_optional() instead of
devm_regulator_get(), which doesn't get a dummy regulator.

> > https://github.com/torvalds/linux/commit/ab0f0987e035f908d670fed7d86efa=
6fac66c0bb
> >=20
> > Without !IS_ERR(pvdd), checking it with regulator_is_enabled(pvdd):
> >=20
> > [ 50.161882] 8<--- cut here ---
> > [ 50.161906] Unable to handle kernel paging request at virtual address =
fffffff9 when read
> > [ 50.161916] [fffffff9] *pgd=3Daffff841, *pte=3D00000000, *ppte=3D00000=
000
> > [ 50.161938] Internal error: Oops: 27 [#1] PREEMPT SMP ARM
> >=20
> > Or disabling it directly with regulator_disable(pvdd):
> >=20
> > [ 69.439827] 8<--- cut here ---
> > [ 69.439841] Unable to handle kernel NULL pointer dereference at virtua=
l address 00000045 when read
> > [ 69.439852] [00000045] *pgd=3D00000000
> > [ 69.439864] Internal error: Oops: 5 [#1] PREEMPT SMP ARM
> >=20
> > Second condition regulator_is_enabled(pvdd) is to make sure that pvdd i=
s
> > disabled with balance.
>=20
>=20
> So you have buggy code and to hide the bug you add checks? No, make the
> code correct so the check is not needed.
>=20

Do you mean that I should use devm_regulator_get() instead in order to get
a dummy regulator, so that it can disable pvdd without unnecessary checks?
Actually there is v4 with those buggy codes and checks dropped.
Please do let me know if I am understanding and doing it correctly. I would
send it after proper period of cooldown.

Regards,
Raymond