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Date:   Wed, 20 Feb 2019 10:05:40 -0800
From:   Brian Norris <briannorris@chromium.org>
To:     egranata@chromium.org
Cc:     hdegoede@redhat.com, mika.westerberg@linux.intel.com,
        dtor@chromium.org, andy.shevchenko@gmail.com, rafael@kernel.org,
        gregkh@linuxfoundation.org, enric.balletbo@collabora.com,
        linux-kernel@vger.kernel.org, gwendal@chromium.org,
        linux-acpi@vger.kernel.org, andriy.shevchenko@linux.intel.com,
        egranata@google.com
Subject: Re: [PATCH v2] driver: platform: Support parsing GpioInt 0 in
 platform_get_irq()
Message-ID: <20190220180538.GA42642@google.com>
References: <20190207185917.167829-1-egranata@google.com>
 <20190211190112.209286-1-egranata@chromium.org>
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Hi,

On Mon, Feb 11, 2019 at 11:01:12AM -0800, egranata@chromium.org wrote:
> From: Enrico Granata <egranata@chromium.org>
> 
> ACPI 5 added support for GpioInt resources as a way to provide
> information about interrupts mediated via a GPIO controller.
> 
> Several device buses (e.g. SPI, I2C) have support for retrieving
> an IRQ specified via this type of resource, and providing it
> directly to the driver as an IRQ number.
> 
> This is not currently done for the platform drivers, as platform_get_irq()
> does not try to parse GpioInt() resources. This requires drivers to
> either have to support only one possible IRQ resource, or to have code
> in place to try both as a failsafe.
> 
> While there is a possibility of ambiguity for devices that exposes
> multiple IRQs, it is easy and feasible to support the common case
> of devices that only expose one IRQ which would be of either type
> depending on the underlying system's architecture.
> 
> This commit adds support for parsing a GpioInt resource in order
> to fulfill a request for the index 0 IRQ for a platform device.
> 
> Signed-off-by: Enrico Granata <egranata@chromium.org>
> ---
> Changes in v2:
>  - only support IRQ index 0
> 
>  drivers/base/platform.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index 1c958eb33ef4d..0d3611cd1b3bc 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -127,7 +127,20 @@ int platform_get_irq(struct platform_device *dev, unsigned int num)
>  		irqd_set_trigger_type(irqd, r->flags & IORESOURCE_BITS);
>  	}
>  
> -	return r ? r->start : -ENXIO;
> +	if (r)
> +		return r->start;
> +
> +	/*
> +	 * For the index 0 interrupt, allow falling back to GpioInt
> +	 * resources. While a device could have both Interrupt and GpioInt
> +	 * resources, making this fallback ambiguous, in many common cases
> +	 * the device will only expose one IRQ, and this fallback
> +	 * allows a common code path across either kind of resource.
> +	 */
> +	if (num == 0 && has_acpi_companion(&dev->dev))
> +		return acpi_dev_gpio_irq_get(ACPI_COMPANION(&dev->dev), num);

For ACPI devices, this changes the return code for a missing interrupt
0 from ENXIO to ENOENT, because acpi_dev_gpio_irq_get() uses ENOENT
instead of ENXIO. While ENXIO isn't exactly documented as the *specific*
error code for a missing interrupt in platform_get_irq(), there are
definitely drivers out there that are looking specifically for ENXIO
(grepping the tree finds several Rockchip platform drivers and a few
ethernet drivers at a minimum). And it also incidentally broke some
usage of the very driver you were trying to support
(drivers/platform/chrome/cros_ec_lpc.c).

I suspect a good strategy here would be to check
acpi_dev_gpio_irq_get()'s return codes here with something like:

	if (ret > 0 || ret == -EPROBE_DEFER)
		return ret;
	return -ENXIO;

Although, the gpiolib functions embedded in there also can return EIO,
so maybe something like this is better?

	if (ret == -ENOENT || ret == 0)
		return -ENXIO;
	return ret;

I'm kinda unsure what to do with error codes besides PROBE_DEFER or
"missing", since most users don't really have it in their mind that
platform_get_irq() can fail with EIO or similar.

Brian

> +
> +	return -ENXIO;
>  #endif
>  }
>  EXPORT_SYMBOL_GPL(platform_get_irq);
> -- 
> 2.20.1.791.gb4d0f1c61a-goog
>