[PATCH V3 2/2] i2c-designware: Add Intel Baytrail PMIC I2C bus support

[David E. Box]

This patch implements an I2C bus sharing mechanism between the host and platform
hardware on select Intel BayTrail SoC platforms using the X-Powers AXP288 PMIC.

On these platforms access to the PMIC must be shared with platform hardware. The
hardware unit assumes full control of the I2C bus and the host must request
access through a special semaphore. Hardware control of the bus also makes it
necessary to disable runtime pm to avoid interfering with hardware transactions.

Signed-off-by: David E. Box <david.e.box@xxxxxxxxxxxxxxx>
---
 drivers/i2c/busses/Kconfig                   |  12 +++
 drivers/i2c/busses/Makefile                  |   1 +
 drivers/i2c/busses/i2c-designware-baytrail.c | 155 +++++++++++++++++++++++++++
 drivers/i2c/busses/i2c-designware-core.h     |   6 ++
 4 files changed, 174 insertions(+)
 create mode 100644 drivers/i2c/busses/i2c-designware-baytrail.c

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index 917c358..d2bfd88 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -464,6 +464,18 @@ config I2C_DESIGNWARE_PCI
 	  This driver can also be built as a module.  If so, the module
 	  will be called i2c-designware-pci.
 
+config I2C_DESIGNWARE_BAYTRAIL
+	bool "Intel Baytrail I2C semaphore support"
+	depends on I2C_DESIGNWARE_PLATFORM=y
+	select IOSF_MBI
+	help
+	  This driver enables host access to the PMIC I2C bus on select Intel
+	  BayTrail platforms using the X-Powers AXP288 PMIC. This driver is
+	  required for host access to the PMIC on these platforms. You should
+	  probably say Y if you have a BayTrail system, unless you know it uses
+	  a different PMIC. Otherwise critical PMIC functions, like charging,
+	  may not operate.
+
 config I2C_EFM32
 	tristate "EFM32 I2C controller"
 	depends on ARCH_EFM32 || COMPILE_TEST
diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
index 78d56c5..48fc23b 100644
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -43,6 +43,7 @@ obj-$(CONFIG_I2C_DESIGNWARE_PLATFORM)	+= i2c-designware-platform.o
 i2c-designware-platform-objs := i2c-designware-platdrv.o
 obj-$(CONFIG_I2C_DESIGNWARE_PCI)	+= i2c-designware-pci.o
 i2c-designware-pci-objs := i2c-designware-pcidrv.o
+obj-$(CONFIG_I2C_DESIGNWARE_BAYTRAIL)	+= i2c-designware-baytrail.o
 obj-$(CONFIG_I2C_EFM32)		+= i2c-efm32.o
 obj-$(CONFIG_I2C_EG20T)		+= i2c-eg20t.o
 obj-$(CONFIG_I2C_EXYNOS5)	+= i2c-exynos5.o
diff --git a/drivers/i2c/busses/i2c-designware-baytrail.c b/drivers/i2c/busses/i2c-designware-baytrail.c
new file mode 100644
index 0000000..ce80241
--- /dev/null
+++ b/drivers/i2c/busses/i2c-designware-baytrail.c
@@ -0,0 +1,155 @@
+/*
+ * Intel BayTrail PMIC I2C bus semaphore implementaion
+ * Copyright (c) 2014, Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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/module.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/acpi.h>
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <asm/iosf_mbi.h>
+#include "i2c-designware-core.h"
+
+#define SEMAPHORE_TIMEOUT	100
+#define PUNIT_SEMAPHORE		0x7
+
+static unsigned long acquired;
+
+static int get_sem(struct device *dev, u32 *sem)
+{
+	u32 reg_val;
+	int ret;
+
+	ret = iosf_mbi_read(BT_MBI_UNIT_PMC, BT_MBI_BUNIT_READ, PUNIT_SEMAPHORE,
+			    &reg_val);
+	if (ret) {
+		dev_err(dev, "iosf failed to read punit semaphore\n");
+		return ret;
+	}
+
+	*sem = reg_val & 0x1;
+
+	return 0;
+}
+
+static void reset_semaphore(struct device *dev)
+{
+	u32 data;
+
+	if (iosf_mbi_read(BT_MBI_UNIT_PMC, BT_MBI_BUNIT_READ,
+				PUNIT_SEMAPHORE, &data)) {
+		dev_err(dev, "iosf failed to reset punit semaphore during read\n");
+		return;
+	}
+
+	data = data & 0xfffffffe;
+	if (iosf_mbi_write(BT_MBI_UNIT_PMC, BT_MBI_BUNIT_WRITE,
+				 PUNIT_SEMAPHORE, data))
+		dev_err(dev, "iosf failed to reset punit semaphore during write\n");
+}
+
+int baytrail_i2c_acquire(struct dw_i2c_dev *dev)
+{
+	u32 sem = 0;
+	int ret;
+	unsigned long start, end;
+
+	if (!dev || !dev->dev)
+		return -ENODEV;
+
+	if (!dev->acquire_lock)
+		return 0;
+
+	/* host driver writes 0x2 to side band semaphore register */
+	ret = iosf_mbi_write(BT_MBI_UNIT_PMC, BT_MBI_BUNIT_WRITE,
+				 PUNIT_SEMAPHORE, 0x2);
+	if (ret) {
+		dev_err(dev->dev, "iosf punit semaphore request failed\n");
+		return ret;
+	}
+
+	/* host driver waits for bit 0 to be set in semaphore register */
+	start = jiffies;
+	end = start + msecs_to_jiffies(SEMAPHORE_TIMEOUT);
+	while (!time_after(jiffies, end)) {
+		ret = get_sem(dev->dev, &sem);
+		if (!ret && sem) {
+			acquired = jiffies;
+			dev_dbg(dev->dev, "punit semaphore acquired after %ums\n",
+				jiffies_to_msecs(jiffies - start));
+			return 0;
+		}
+
+		usleep_range(1000, 2000);
+	}
+
+	dev_err(dev->dev, "punit semaphore timed out, resetting\n");
+	reset_semaphore(dev->dev);
+
+	ret = iosf_mbi_read(BT_MBI_UNIT_PMC, BT_MBI_BUNIT_READ,
+		PUNIT_SEMAPHORE, &sem);
+	if (!ret)
+		dev_err(dev->dev, "iosf failed to read punit semaphore\n");
+	else
+		dev_err(dev->dev, "PUNIT SEM: %d\n", sem);
+
+	WARN_ON(1);
+
+	return -ETIMEDOUT;
+}
+EXPORT_SYMBOL(baytrail_i2c_acquire);
+
+void baytrail_i2c_release(struct dw_i2c_dev *dev)
+{
+	if (!dev || !dev->dev)
+		return;
+
+	if (!dev->acquire_lock)
+		return;
+
+	reset_semaphore(dev->dev);
+	dev_dbg(dev->dev, "punit semaphore held for %ums\n",
+		jiffies_to_msecs(jiffies - acquired));
+}
+EXPORT_SYMBOL(baytrail_i2c_release);
+
+void i2c_dw_eval_lock_support(struct dw_i2c_dev *dev)
+{
+	acpi_status status;
+	unsigned long long shared_host = 0;
+	acpi_handle handle;
+
+	if (!dev || !dev->dev)
+		return;
+
+	handle = ACPI_HANDLE(dev->dev);
+	if (!handle)
+		return;
+
+	status = acpi_evaluate_integer(handle, "_SEM", NULL, &shared_host);
+
+	if (ACPI_FAILURE(status))
+		return;
+
+	if (shared_host) {
+		dev_info(dev->dev, "I2C bus managed by PUNIT\n");
+		dev->acquire_lock = baytrail_i2c_acquire;
+		dev->release_lock = baytrail_i2c_release;
+		dev->pm_runtime_disabled = true;
+	}
+}
+EXPORT_SYMBOL(i2c_dw_eval_lock_support);
+
+MODULE_AUTHOR("David E. Box <david.e.box@xxxxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("Baytrail I2C Semaphore driver");
+MODULE_LICENSE("GPL v2");
diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
index a472c91..72ddfa8 100644
--- a/drivers/i2c/busses/i2c-designware-core.h
+++ b/drivers/i2c/busses/i2c-designware-core.h
@@ -129,3 +129,9 @@ extern void i2c_dw_disable(struct dw_i2c_dev *dev);
 extern void i2c_dw_clear_int(struct dw_i2c_dev *dev);
 extern void i2c_dw_disable_int(struct dw_i2c_dev *dev);
 extern u32 i2c_dw_read_comp_param(struct dw_i2c_dev *dev);
+
+#if IS_ENABLED(CONFIG_I2C_DESIGNWARE_BAYTRAIL)
+extern void i2c_dw_eval_lock_support(struct dw_i2c_dev *dev);
+#else
+static inline void i2c_dw_eval_lock_support(struct dw_i2c_dev *dev) { }
+#endif
-- 
1.9.1

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