linux-kernel - [PATCH 5/5] platform/chrome: cros_ec_spi: Set PROBE_PREFER

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Date:   Fri, 28 Oct 2022 14:14:49 -0700
From:   Brian Norris <briannorris@...omium.org>
To:     Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>
Cc:     chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>
Subject: [PATCH 5/5] platform/chrome: cros_ec_spi: Set PROBE_PREFER_ASYNCHRONOUS

This driver often takes on the order of 10ms to start, but in some cases
as much as 600ms [1]. It shouldn't have many cross-device dependencies
to race with, nor racy access to shared state with other drivers, so
this should be a relatively low risk change.

This driver was pinpointed as part of a survey of top slowest initcalls
(i.e., are built in, and probing synchronously) on a lab of ChromeOS
systems.

[1] 600ms was especially surprising to me, so I checked a little deeper.
This driver is used to interface with Embedded Controllers besides just
the traditional laptop power-state controller -- it also interfaces with
some fingerprint readers, which may start up in parallel with the
kernel, or which may not even be present on some SKUs, despite having a
node for it. Thus, our time is wasted just timing out talking to it. At
least we can do that without blocking everyone else.

Signed-off-by: Brian Norris <briannorris@...omium.org>
---

 drivers/platform/chrome/cros_ec_spi.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/platform/chrome/cros_ec_spi.c b/drivers/platform/chrome/cros_ec_spi.c
index 7360b3ff6e4f..21143dba8970 100644
--- a/drivers/platform/chrome/cros_ec_spi.c
+++ b/drivers/platform/chrome/cros_ec_spi.c
@@ -834,6 +834,7 @@ static struct spi_driver cros_ec_driver_spi = {
 		.name	= "cros-ec-spi",
 		.of_match_table = cros_ec_spi_of_match,
 		.pm	= &cros_ec_spi_pm_ops,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
 	},
 	.probe		= cros_ec_spi_probe,
 	.remove		= cros_ec_spi_remove,
-- 
2.38.1.273.g43a17bfeac-goog