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

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Message-Id: <20210521221906.199436-1-kyle.meyer@hpe.com>
Date:   Fri, 21 May 2021 17:19:06 -0500
From:   Kyle Meyer <kyle.meyer@....com>
To:     rjw@...ysocki.net, viresh.kumar@...aro.org,
        linux-kernel@...r.kernel.org
Cc:     linux-pm@...r.kernel.org, linux-acpi@...r.kernel.org,
        Kyle Meyer <kyle.meyer@....com>
Subject: [PATCH] acpi-cpufreq: Skip initialization if a cpufreq driver exists

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@....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