Re: [RFC PATCH 1/2] platform/surface: aggregator: Defer probing when serdev is not ready

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Thu, May 02, 2024 at 12:02:46PM +0800, Weifeng Liu wrote:
> This is an attempt to alleviate race conditions in the SAM driver where
> essential resources like serial device and GPIO pins are not ready at
> the time ssam_serial_hub_probe() is called.  Instead of giving up
> probing, a better way would be to defer the probing by returning
> -EPROBE_DEFER, allowing the kernel try again later.
> 
> However, there is no way of identifying all such cases from other real
> errors in a few days.  So let's take a gradual approach identify and
> address these cases as they arise.  This commit marks the initial step
> in this process.

...

> +	/* The following step can fail when it's called too early before the
> +	 * underlying uart device is ready (in this case -ENXIO is returned).

UART

> +	 * Instead of simply giving up and losing everything, we can defer
> +	 * the probing by returning -EPROBE_DEFER so that the kernel would be
> +	 * able to retry later. */

/*
 * Use correct style for the comments.
 * Here is the example.
 */

>  	status = serdev_device_open(serdev);
> -	if (status)
> +	if (status == -ENXIO)
> +		status = -EPROBE_DEFER;
> +	if (status) {
> +		dev_err_probe(&serdev->dev, status,
> +			      "failed to open serdev device\n");
>  		goto err_devopen;
> +	}

...

Hans, not sure if it helps, but we added similar into I²C and SPI code.

2dea645ffc21 ("i2c: acpi: Return error pointers from i2c_acpi_new_device()")

9c22ec4ac27b ("spi: Return deferred probe error when controller isn't yet available")

-- 
With Best Regards,
Andy Shevchenko