linux-kernel - Re: [PATCH] gpiolib: acpi: use the fwnode in acpi_gpiochip

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Date:   Fri, 10 Mar 2023 13:41:50 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Daniel Kaehn <kaehndan@...il.com>, linux-gpio@...r.kernel.org,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpiolib: acpi: use the fwnode in acpi_gpiochip_find()

On Thu, Mar 09, 2023 at 02:40:51PM +0100, Benjamin Tissoires wrote:
> While trying to set up an SSDT override for a USB-2-I2C chip [0],
> I realized that the function acpi_gpiochip_find() was using the parent
> of the gpio_chip to do the ACPI matching.
> 
> This works fine on my icelake laptop because AFAICT, the DSDT presents
> the PCI device INT3455 as the "Device (GPI0)", but is in fact handled
> by the pinctrl driver in Linux.
> The pinctrl driver then creates a gpio_chip device. This means that the
> gc->parent device in that case is the GPI0 device from ACPI and everything
> works.
> 
> However, in the hid-cp2112 case, the parent is the USB device, and the
> gpio_chip is directly under that USB device. Which means that in this case
> gc->parent points at the USB device, and so we can not do an ACPI match
> towards the GPIO device.
> 
> I think it is safe to resolve the ACPI matching through the fwnode
> because when we call gpiochip_add_data(), the first thing it does is
> setting a proper gc->fwnode: if it is not there, it borrows the fwnode
> of the parent.
> 
> So in my icelake case, gc->fwnode is the one from the parent, meaning
> that the ACPI handle we will get is the one from the GPI0 in the DSDT
> (the pincrtl one). And in the hid-cp2112 case, we get the actual
> fwnode from the gpiochip we created in the HID device, making it working.
> 
> Link: https://lore.kernel.org/linux-input/20230227140758.1575-1-kaehndan@gmail.com/T/#m592f18081ef3b95b618694a612ff864420c5aaf3 [0]
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>

Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>