[PATCH] iio: sx9310: Prefer async probe

[Douglas Anderson]

On one board I found that:
  probe of 5-0028 returned 1 after 259547 usecs

There's no reason to block probe of all other devices on our probe.
Turn on async probe.

Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---
NOTE: I haven't done any analysis of the driver to see _why_ it's so
slow, only that I have measured it to be slow.  Someone could
certainly take the time to profile / optimize it, but in any case it
still won't hurt to be async.

This is a very safe flag to turn on since:

1. It's not like our probe order was defined by anything anyway.  When
we probe is at the whim of when our i2c controller probes and that can
be any time.

2. If some other driver needs us then they have to handle the fact
that we might not have probed yet anyway.

3. There may be other drivers probing at the same time as us anyway
because _they_ used async probe.

While I won't say that it's impossible to tickle a bug by turning on
async probe, I would assert that in almost all cases the bug was
already there and needed to be fixed anyway.

ALSO NOTE: measurement / testing was done on the downstream Chrome OS
5.4 tree.  I confirmed compiling on mainline.

 drivers/iio/proximity/sx9310.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/iio/proximity/sx9310.c b/drivers/iio/proximity/sx9310.c
index dc2e11b43431..444cafc53408 100644
--- a/drivers/iio/proximity/sx9310.c
+++ b/drivers/iio/proximity/sx9310.c
@@ -1054,6 +1054,7 @@ static struct i2c_driver sx9310_driver = {
 		.acpi_match_table = ACPI_PTR(sx9310_acpi_match),
 		.of_match_table = of_match_ptr(sx9310_of_match),
 		.pm = &sx9310_pm_ops,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
 	},
 	.probe		= sx9310_probe,
 	.id_table	= sx9310_id,
-- 
2.28.0.402.g5ffc5be6b7-goog