linux-kernel - Re: [PATCH v2] PCI: dra7xx: Fix reset behaviour

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Message-ID: <CACRpkdai2cvoNFR8yH2MHP+R27nQm1HZNK4-mJ50mE7DHrBmXw@mail.gmail.com>
Date:   Fri, 25 Jun 2021 01:18:43 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Pali Rohár <pali@...nel.org>
Cc:     Luca Ceresoli <luca@...aceresoli.net>,
        Kishon Vijay Abraham I <kishon@...com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        linux-pci <linux-pci@...r.kernel.org>,
        Linux-OMAP <linux-omap@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v2] PCI: dra7xx: Fix reset behaviour

On Wed, Jun 23, 2021 at 12:23 AM Pali Rohár <pali@...nel.org> wrote:

> Lorenzo asked a good question how GPIO drives PERST#. And maybe it would
> be a good idea to unify all pci controller drivers to use same GPIO
> value for asserting PERST# pin. If it is possible. As we can see it is a
> big mess.
>
> Personally I would like to a see two helper functions like
>
>   void pcie_assert_perst(struct gpio_desc *gpio);
>   void pcie_deassert_perst(struct gpio_desc *gpio);
>
> which pci controller driver will use and we will not more handle active
> high / low state or polarity inversion and meditate if gpio set to zero
> means assert or de-assert.

GPIO descriptors (as are used in this driver) are supposed to hide
and encapsulate polarity inversion so:

gpiod_set_value(gpiod, 1) == assert the line
gpiod_set_value(gpiod, 0) == de-assert the line

Whether the line is asserted by physically driving the line low or
high should not be a concern, that is handled in the machine
description, we support OF, ACPI and even board files to
define this.

I would use gpiod_set_value() directly as above and maybe
add some comments explaining what is going on and that
the resulting polarity inversion is handled inside gpiolib.

Because of common misunderstandings we have pondered to just
search/replace the last argument of gpiod_set_value() from
an (int value) to a (bool asserted) to make things clear.
I just never get around to do that.

Yours,
Linus Walleij