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SubjectRe: [PATCH v2 2/2] input: soc_button_array for newer surface devices
Hi Maximilian,

On Tue, Jul 02, 2019 at 02:37:40AM +0200, Maximilian Luz wrote:
> Power and volume button support for 5th and 6th genration Microsoft
> Surface devices via soc_button_array.
>
> Note that these devices use the same MSHW0040 device as on the Surface
> Pro 4, however the implementation is different (GPIOs vs. ACPI
> notifications). Thus some checking is required to ensure we only load
> this driver on the correct devices.

When you are saying that Pro 4 and later models use different
notifications, does this mean that Pro 4 does not define any GPIOs? If
so can we use their presence as indicator whether we should be using
this driver or not. I would like to avoid repeating the ACPI parsing
code that you have in the platform driver.

> +static int soc_device_check_MSHW0040(struct device *dev)
> +{
> + acpi_handle handle = ACPI_HANDLE(dev);
> + union acpi_object *result;
> + u64 oem_platform_rev = 0;
> + int gpios;
> +
> + // get OEM platform revision
> + result = acpi_evaluate_dsm_typed(handle, &MSHW0040_DSM_UUID,
> + MSHW0040_DSM_REVISION,
> + MSHW0040_DSM_GET_OMPR, NULL,
> + ACPI_TYPE_INTEGER);
> +
> + if (result) {
> + oem_platform_rev = result->integer.value;
> + ACPI_FREE(result);
> + }
> +
> + if (oem_platform_rev == 0)
> + return -ENODEV;
> +
> + dev_dbg(dev, "OEM Platform Revision %llu\n", oem_platform_rev);
> +
> + /*
> + * We are _really_ expecting GPIOs here. If we do not get any, this
> + * means the GPIO driver has not been loaded yet (which can happen).
> + * Try again later.
> + */
> + gpios = gpiod_count(dev, NULL);
> + if (gpios < 0)
> + return -EAGAIN;

I do not believe -EAGAIN has any special meaning in the driver core;
also when the GPIO controller is not ready gpiod_get() will return
-EPROBE_DEFER, which is the prober way if signalling that some resource
is not yet available and probe should be retries at a later time.

Moreover, I do not believe that gpiod_count() needs GPIO controller to
be ready, the count is taken from board firmware or static board file
definition, so if gpiod_count() returns 0 it should be clear indication
that the driver should not be used with the device.

Thanks.

--
Dmitry

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