[RFC,1/2] ACPI: Add support for Platform Communication Channel

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index cbc5dfc..8893fa5 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -361,6 +361,16 @@  config ACPI_REDUCED_HARDWARE_ONLY
 
 	If you are unsure what to do, do not enable this option.
 
+config ACPI_PCC
+	bool "ACPI Platform Communication Channel"
+	def_bool n
+	depends on ACPI
+	help
+	Enable this option if your platform supports PCC as defined in the
+	ACPI spec 5.0a+. PCC is a generic mechanism for the OS to communicate
+	with a platform such as a BMC. PCC is typically used by CPPC, RAS
+	and MPST. 
+
 source "drivers/acpi/apei/Kconfig"
 
 config ACPI_EXTLOG
diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
index fc133d4..d8aa613 100644
--- a/drivers/acpi/Makefile
+++ b/drivers/acpi/Makefile
@@ -74,7 +74,7 @@  obj-$(CONFIG_ACPI_HED)		+= hed.o
 obj-$(CONFIG_ACPI_EC_DEBUGFS)	+= ec_sys.o
 obj-$(CONFIG_ACPI_CUSTOM_METHOD)+= custom_method.o
 obj-$(CONFIG_ACPI_BGRT)		+= bgrt.o
-
+obj-$(CONFIG_ACPI_PCC)		+= pcc.o
 # processor has its own "processor." module_param namespace
 processor-y			:= processor_driver.o processor_throttling.o
 processor-y			+= processor_idle.o processor_thermal.o
diff --git a/drivers/acpi/pcc.c b/drivers/acpi/pcc.c
new file mode 100644
index 0000000..7961ad6
--- /dev/null
+++ b/drivers/acpi/pcc.c
@@ -0,0 +1,194 @@ 
+/*
+ *	Copyright (C) 2014 Linaro Ltd.
+ *	Author:	Ashwin Chaugule <ashwin.chaugule@linaro.org>
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ */
+
+#include <linux/acpi.h>
+#include <linux/io.h>
+#include <linux/uaccess.h>
+#include <linux/init.h>
+#include <linux/cpufreq.h>
+#include <linux/delay.h>
+#include <linux/ioctl.h>
+#include <linux/vmalloc.h>
+
+#include <acpi/actbl.h>
+
+#define MAX_PCC_SUBSPACES	256
+#define PCCS_SS_SIG_MAGIC	0x50434300
+#define GEN_SCI_SHIFT		0x15
+#define PCC_CMD_COMPLETE	0x1
+
+/* Array of pointers to Type 0 Generic Communication Subspace Structures */
+struct acpi_pcct_subspace *pcc_ss_arr[MAX_PCC_SUBSPACES];
+
+/*
+ * TODO: Serialize OSPM control flow per PCC channel.
+ */
+static DEFINE_SPINLOCK(pcc_lock);
+
+/* Total number of subspaces detected in PCCT. */
+static int total_ss;
+
+/*
+ * PCC clients call this function to get a base address of their
+ * Communication channel
+ */
+int get_pcc_comm_channel(u32 ss_idx, u64 __iomem *addr, int *len)
+{
+	struct acpi_pcct_subspace *pcct_subspace = pcc_ss_arr[ss_idx];
+
+	if (pcct_subspace) {
+		*addr = pcct_subspace->base_address;
+		*len = pcct_subspace->length;
+	} else
+		return -EINVAL;
+
+	return 0;
+}
+
+/* Send PCC cmd on behalf of this (subspace id) PCC client */
+u16 send_pcc_cmd(u8 cmd, u8 sci, u32 ss_idx, u64 __iomem *base_addr)
+{
+	struct acpi_pcct_subspace *pcct_subspace = pcc_ss_arr[ss_idx];
+	struct acpi_pcct_shared_memory *generic_comm_base =
+		(struct acpi_pcct_shared_memory *)base_addr;
+	struct acpi_generic_address doorbell;
+	u16 pcc_cmd;
+	u64 doorbell_preserve;
+	u64 doorbell_val;
+	u64 doorbell_write;
+	/* 
+	 * Min time in usec that OSPM is expected to wait
+	 * before sending the next PCC cmd.
+	 */
+	u16 cmd_delay = pcct_subspace->min_turnaround_time;
+
+	if (!generic_comm_base) {
+		pr_err("No Generic Communication Channel provided.\n");
+		return -EINVAL;
+	}
+
+	spin_lock(&pcc_lock);
+
+	/* TODO: Add support for SCI. */
+	pcc_cmd |= cmd;
+
+	/* Get doorbell details for this subspace. */
+	doorbell = pcct_subspace->doorbell_register;
+	doorbell_preserve = pcct_subspace->preserve_mask;
+	doorbell_write = pcct_subspace->write_mask;
+
+	/* Loop until CMD complete bit is set. For prev cmds. */
+	while (!(ioread16(&generic_comm_base->status) & PCC_CMD_COMPLETE))
+		udelay(cmd_delay);
+
+	/* Write to the shared comm region. */
+	iowrite16(cmd, &generic_comm_base->command);
+
+	iowrite32((PCCS_SS_SIG_MAGIC | ss_idx), &generic_comm_base->signature);
+
+	/* Flip CMD COMPLETE bit */
+	/* TODO: When we add SCI support then preserve SCI status bit. */
+	iowrite16(0, &generic_comm_base->status);
+
+	/* Sync notification from OSPM to Platform. */
+	acpi_read(&doorbell_val, &doorbell);
+	acpi_write((doorbell_val & doorbell_preserve) | doorbell_write,
+			&doorbell);
+
+	/* Wait for Platform to consume. */
+	while (!(ioread16(&generic_comm_base->status) & PCC_CMD_COMPLETE))
+		udelay(cmd_delay);
+
+	spin_unlock(&pcc_lock);
+
+	/* PCC clients should check for ERR */
+	return generic_comm_base->status;
+}
+
+static int parse_pcc_subspace(struct acpi_subtable_header *header,
+		const unsigned long end)
+{
+	struct acpi_pcct_subspace *pcct_ss;
+
+	pcct_ss = (struct acpi_pcct_subspace*) header;
+
+	if (pcct_ss->header.type != ACPI_PCCT_TYPE_GENERIC_SUBSPACE) {
+		pr_err("Incorrect PCC Subspace type detected\n");
+		return -EINVAL;
+	}
+
+	/* TODO: Replace with idr API. */
+	pcc_ss_arr[total_ss++] = pcct_ss;
+
+	return 0;
+}
+
+static int __init pcc_probe(void)
+{
+	acpi_status status = AE_OK;
+	acpi_size pcct_tbl_header_size;
+	struct acpi_table_pcct *pcct_tbl;
+
+	/* Search for PCCT */
+	status = acpi_get_table_with_size(ACPI_SIG_PCCT, 0,
+			(struct acpi_table_header **)&pcct_tbl,
+			&pcct_tbl_header_size);
+
+	if (ACPI_SUCCESS(status) && !pcct_tbl) {
+		pr_warn("PCCT header not found.\n");
+		status = AE_NOT_FOUND;
+		goto out_err;
+	}
+
+	/* Found PCCT. Enumerate PCC subspaces.
+	 * Currently there is only type of Subspace
+	 * defined in the ACPI 5.0 spec. If there 
+	 * is more than one type, then we'll need 
+	 * to rework this to parse multiple types of
+	 * subspaces.
+	 */
+	status = acpi_table_parse_entries(ACPI_SIG_PCCT,
+			sizeof(struct acpi_table_pcct), ACPI_PCCT_TYPE_GENERIC_SUBSPACE,
+			parse_pcc_subspace, MAX_PCC_SUBSPACES);
+
+	if (ACPI_SUCCESS(status))
+		pr_err("Error parsing PCC subspaces from PCCT\n");
+
+	pr_info("Detected %d PCC Subspaces\n", total_ss);
+
+out_err:
+	return (ACPI_SUCCESS(status) ? 1 : 0);
+}
+
+static int __init pcc_init(void)
+{
+	int ret;
+
+	if (acpi_disabled)
+		return -ENODEV;
+
+	/* Check if PCC support is available. */
+	ret = pcc_probe();
+
+	if (ret) {
+		pr_debug("PCC probe failed.\n");
+		return -EINVAL;
+	}
+
+	return ret;
+}
+
+device_initcall(pcc_init);