cpufreq: acpi-cpufreq: Skip initialization if cpufreq driver is present

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

acpi-cpufreq is mutually exclusive with intel_pstate, but
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.

Fixes: 75c0758137c7a ("acpi-cpufreq: Fail initialization if driver cannot be registered")
Signed-off-by: Kyle Meyer <kyle.meyer@hpe.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 7e7450453714d3d77d3a0cec0020a2edb6e9e8e7..e79a945369d113fc5bd894ec8fab49a92351e2c6 100644 (file)
--- 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__);