linux-kernel - Re: [PATCH RFT/RFC 2/2] mfd: cs42l43: use GPIO machine lookup for cs-gpios

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMRc=MdYJ0+yXziHB5ok40yUJMyYPKPt0K5COXDm3tM6dWqAJQ@mail.gmail.com>
Date: Wed, 19 Nov 2025 17:28:54 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Charles Keepax <ckeepax@...nsource.cirrus.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, David Rhodes <david.rhodes@...rus.com>, 
	Richard Fitzgerald <rf@...nsource.cirrus.com>, Lee Jones <lee@...nel.org>, 
	Mark Brown <broonie@...nel.org>, Maciej Strozek <mstrozek@...nsource.cirrus.com>, 
	Andy Shevchenko <andy@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-sound@...r.kernel.org, 
	patches@...nsource.cirrus.com, linux-spi@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH RFT/RFC 2/2] mfd: cs42l43: use GPIO machine lookup for cs-gpios

On Wed, Nov 19, 2025 at 4:52 PM Charles Keepax
<ckeepax@...nsource.cirrus.com> wrote:
>
> On Wed, Nov 19, 2025 at 04:35:07PM +0100, Bartosz Golaszewski wrote:
> > On Wed, Nov 19, 2025 at 4:21 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> > >
> > > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > >
> > > Currently the SPI driver sets up a software node referencing the GPIO
> > > controller exposing the chip-select GPIO but this node never gets
> > > attached to the actual GPIO provider. The lookup uses the weird way GPIO
> > > core performs the software node lookup by the swnode's name. We want to
> > > switch to a true firmware node lookup in GPIO core but without the true
> > > link, this driver will break.
> > >
> > > We can't use software nodes as only one software node per device is
> > > allowed and the ACPI node the MFD device uses has a secondary node
> > > already attached.
> > >
> > > Let's switch to GPIO machine lookup instead.
> > >
> > > Fixes: 439fbc97502a ("spi: cs42l43: Add bridged cs35l56 amplifiers")
> > > Reported-by: Charles Keepax <ckeepax@...nsource.cirrus.com>
> > > Closes: https://lore.kernel.org/all/aRyf7qDdHKABppP8@opensource.cirrus.com/
> > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > > ---
> > >
> > > +static struct gpiod_lookup_table cs42l43_gpio_lookup = {
> > > +       .dev_id = "cs42l43-spi",
> > > +       .table = {
> > > +               GPIO_LOOKUP("cs42l43-pinctrl", 0, "cs", GPIO_ACTIVE_LOW),
> > > +               GPIO_LOOKUP(INIT_ERR_PTR(-ENOENT), 0, "cs", 0),
> >
> > I sent the wrong version, sorry. This should have been:
> >
> > GPIO_LOOKUP_IDX("cs42l43-pinctrl", 0, "cs", 0, GPIO_ACTIVE_LOW),
> > GPIO_LOOKUP_IDX(INIT_ERR_PTR(-ENOENT), 0, "cs", 1, 0),
> >
> > Charles: Can you fix it up yourself before testing?
>
> Yeah can do, but I am still very nervous about how this approach
> interacts with device tree and ACPI systems doing things
> normally. Is this also ignored if the firmware specifies the
> properties correctly? I feel like if we go this route I am going
> to have to bring up a few extra things to test on as its quite a
> big change.
>

The machine lookup always comes after the firmware node lookup. Even
after the secondary node. It's the last-ditch effort to find a match
actually.

> Apologies for the delay on my suggestion but something weird is
> happening deep in the swnode stuff and its taking me ages to peel
> back all the layers of in abstraction there. It seems something
> copies all the properties and somehow the fwnode I want doesn't
> make it through that process. But the basic idea is like:
>
> props = devm_kmemdup(priv->dev, cs42l43_cs_props,
>                      sizeof(cs42l43_cs_props), GFP_KERNEL);
> if (!props)
>         return -ENOMEM;
>
> args = devm_kmemdup(priv->dev, cs42l43_cs_refs,
>                     sizeof(cs42l43_cs_refs), GFP_KERNEL);
> if (!args)
>         return -ENOMEM;
>
> args[0].fwnode = fwnode;
> props->pointer = props;
>
> ie. As your patches add support for using the geniune firmware
> node just do so.
>

But do you have the firmware node at the time of doing the above? The
software node must first be registered with the swnode subsystem to
become an actual firmware node. Only then can you reference it by its
firmware node address.

Bart