ACPI: cpufreq: Use platform devices to load ACPI PPC and PCC drivers

The acpi-cpufreq and pcc-cpufreq drivers are loaded through per-CPU
module aliases. This can result in many unnecessary load requests during
boot if another frequency module, such as intel_pstate, is already
active. For instance, on a typical Intel system, one can observe that
udev makes 2x#CPUs attempts to insert acpi_cpufreq and 1x#CPUs attempts
for pcc_cpufreq. All these tries then fail if another frequency module
is already registered.

In the worst case, without the recent fix in commit 0254127ab977e
("module: Don't wait for GOING modules"), these module loads occupied
all udev workers and had their initialization attempts ran sequentially.
Resolving all these loads then on some larger machines took too long,
prevented other hardware from getting its drivers initialized and
resulted in a failed boot. Discussion over these duplicate module
requests ended up with a conclusion that only one load attempt should be
ideally made.

Both acpi-cpufreq and pcc-cpufreq drivers use platform firmware controls
which are defined by ACPI. It is possible to treat these interfaces as
platform devices.

The patch extends the ACPI parsing logic to check the ACPI namespace if
the PPC or PCC interface is present and creates a virtual platform
device for each if it is available. The acpi-cpufreq and pcc-cpufreq
drivers are then updated to map to these devices.

This allows to try loading acpi-cpufreq and pcc-cpufreq only once during
boot and only if a given interface is available in the firmware.

Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
[ rjw: whitespace and error message log level adjustments, subject edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 40 insertions, 2 deletions

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index 6737b1cbf6d6..f9aa02cac6d1 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -15,6 +15,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/pci.h>
+#include <linux/platform_device.h>
 
 #include <acpi/processor.h>
 
@@ -148,6 +149,34 @@ static int acpi_processor_errata(void)
 	return result;
 }
 
+/* Create a platform device to represent a CPU frequency control mechanism. */
+static void cpufreq_add_device(const char *name)
+{
+	struct platform_device *pdev;
+
+	pdev = platform_device_register_simple(name, PLATFORM_DEVID_NONE, NULL, 0);
+	if (IS_ERR(pdev))
+		pr_info("%s device creation failed: %ld\n", name, PTR_ERR(pdev));
+}
+
+#ifdef CONFIG_X86
+/* Check presence of Processor Clocking Control by searching for \_SB.PCCH. */
+static void __init acpi_pcc_cpufreq_init(void)
+{
+	acpi_status status;
+	acpi_handle handle;
+
+	status = acpi_get_handle(NULL, "\\_SB", &handle);
+	if (ACPI_FAILURE(status))
+		return;
+
+	if (acpi_has_method(handle, "PCCH"))
+		cpufreq_add_device("pcc-cpufreq");
+}
+#else
+static void __init acpi_pcc_cpufreq_init(void) {}
+#endif /* CONFIG_X86 */
+
 /* Initialization */
 #ifdef CONFIG_ACPI_HOTPLUG_CPU
 int __weak acpi_map_cpu(acpi_handle handle,
@@ -280,14 +309,22 @@ static int acpi_processor_get_info(struct acpi_device *device)
 		dev_dbg(&device->dev, "Failed to get CPU physical ID.\n");
 
 	pr->id = acpi_map_cpuid(pr->phys_id, pr->acpi_id);
-	if (!cpu0_initialized && !acpi_has_cpu_in_madt()) {
+	if (!cpu0_initialized) {
 		cpu0_initialized = 1;
 		/*
 		 * Handle UP system running SMP kernel, with no CPU
 		 * entry in MADT
 		 */
-		if (invalid_logical_cpuid(pr->id) && (num_online_cpus() == 1))
+		if (!acpi_has_cpu_in_madt() && invalid_logical_cpuid(pr->id) &&
+		    (num_online_cpus() == 1))
 			pr->id = 0;
+		/*
+		 * Check availability of Processor Performance Control by
+		 * looking at the presence of the _PCT object under the first
+		 * processor definition.
+		 */
+		if (acpi_has_method(pr->handle, "_PCT"))
+			cpufreq_add_device("acpi-cpufreq");
 	}
 
 	/*
@@ -686,6 +723,7 @@ void __init acpi_processor_init(void)
 	acpi_processor_check_duplicates();
 	acpi_scan_add_handler_with_hotplug(&processor_handler, "processor");
 	acpi_scan_add_handler(&processor_container_handler);
+	acpi_pcc_cpufreq_init();
 }
 
 #ifdef CONFIG_ACPI_PROCESSOR_CSTATE