[PATCH] acpi-cpufreq: Skip initialization if a cpufreq driver exists

From: <kyle.meyer@hpe.com>
To: <rjw@rjwysocki.net>, <viresh.kumar@linaro.org>,
	<linux-kernel@vger.kernel.org>
Cc: Kyle Meyer <kyle.meyer@hpe.com>
Subject: [PATCH] acpi-cpufreq: Skip initialization if a cpufreq driver exists
Date: Tue, 18 May 2021 14:34:55 -0500	[thread overview]
Message-ID: <20210518193455.192796-1-kyle.meyer@hpe.com> (raw)

From: Kyle Meyer <kyle.meyer@hpe.com>

Revert part of commit 75c0758137c7a
("acpi-cpufreq: Fail initialization if driver cannot be registered").

acpi-cpufreq is mutually exclusive with intel_pstate, however,
acpi-cpufreq is loaded multiple times during startup while intel_pstate is
enabled. On systems using systemd the kernel triggers one uevent for each
device as a result of systemd-udev-trigger.service. The service exists to
retrigger all devices as uevents sent by the kernel before systemd-udevd
is running are missed. The delay caused by systemd-udevd repeatedly loading
the driver, getting a fail return, and unloading the driver twice per
logical CPU has a significant impact on the startup time, and can cause
some devices to be unavailable after reaching the root login prompt.

Load the driver once but skip initialization if a cpufreq driver exists by
changing the return value of cpufreq_get_current_driver() from -EEXIST to
0.

Signed-off-by: Kyle Meyer <kyle.meyer@hpe.com>
---
 drivers/cpufreq/acpi-cpufreq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 7e7450453714..e79a945369d1 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -1003,7 +1003,7 @@ static int __init acpi_cpufreq_init(void)
 
 	/* don't keep reloading if cpufreq_driver exists */
 	if (cpufreq_get_current_driver())
-		return -EEXIST;
+		return 0;
 
 	pr_debug("%s\n", __func__);
 
-- 
2.26.2
