[PATCH] i2c-designware: 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 XPower 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                  |  10 +++
 drivers/i2c/busses/Makefile                 |   1 +
 drivers/i2c/busses/i2c-designware-core.h    |  14 ++++
 drivers/i2c/busses/i2c-designware-platdrv.c |  78 +++++++++++++++++++--
 drivers/i2c/busses/i2c-shared-controller.c  | 101 ++++++++++++++++++++++++++++
 5 files changed, 200 insertions(+), 4 deletions(-)
 create mode 100644 drivers/i2c/busses/i2c-shared-controller.c

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index 2ac87fa..672ef23 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -441,6 +441,16 @@ 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_SHARED_CONTROLLER
+	tristate "Intel Baytrail PMIC shared I2C bus support"
+	depends on ACPI
+	select IOSF_MBI
+	select I2C_DESIGNWARE_CORE
+	help
+	  This driver enables shared access to the PMIC I2C bus on select Intel
+	  BayTrail platforms using the XPower AXP288 PMIC. This driver is
+	  required for host access to the PMIC on these platforms.
+
 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 49bf07e..33d62d1 100644
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -41,6 +41,7 @@ obj-$(CONFIG_I2C_DESIGNWARE_CORE)	+= i2c-designware-core.o
 obj-$(CONFIG_I2C_DESIGNWARE_PLATFORM)	+= i2c-designware-platform.o
 i2c-designware-platform-objs := i2c-designware-platdrv.o
 obj-$(CONFIG_I2C_DESIGNWARE_PCI)	+= i2c-designware-pci.o
+obj-$(CONFIG_I2C_SHARED_CONTROLLER)	+= i2c-shared-controller.o
 i2c-designware-pci-objs := i2c-designware-pcidrv.o
 obj-$(CONFIG_I2C_EFM32)		+= i2c-efm32.o
 obj-$(CONFIG_I2C_EG20T)		+= i2c-eg20t.o
diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
index d66b6cb..a2b72f4 100644
--- a/drivers/i2c/busses/i2c-designware-core.h
+++ b/drivers/i2c/busses/i2c-designware-core.h
@@ -65,6 +65,10 @@
  * @ss_lcnt: standard speed LCNT value
  * @fs_hcnt: fast speed HCNT value
  * @fs_lcnt: fast speed LCNT value
+ * @shared_host: if host must share access to adapter with other
+ * firmware/hardware units
+ * @acquire_ownership: function to acquire exclusive use of the controller
+ * @release_ownership: function to release exclusive use of the controller
  *
  * HCNT and LCNT parameters can be used if the platform knows more accurate
  * values than the one computed based only on the input clock frequency.
@@ -105,6 +109,11 @@ struct dw_i2c_dev {
 	u16			ss_lcnt;
 	u16			fs_hcnt;
 	u16			fs_lcnt;
+#if IS_ENABLED(CONFIG_I2C_SHARED_CONTROLLER)
+	int			shared_host;
+	int			(*acquire_ownership)(struct device *dev);
+	int			(*release_ownership)(struct device *dev);
+#endif
 };
 
 #define ACCESS_SWAP		0x00000001
@@ -123,3 +132,8 @@ 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_SHARED_CONTROLLER)
+extern int i2c_acquire_ownership(struct device *dev);
+extern int i2c_release_ownership(struct device *dev);
+#endif
diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
index f9b1dec..f86c285 100644
--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -52,6 +52,32 @@ static u32 i2c_dw_get_clk_rate_khz(struct dw_i2c_dev *dev)
 	return clk_get_rate(dev->clk)/1000;
 }
 
+#if IS_ENABLED(CONFIG_I2C_SHARED_CONTROLLER)
+int i2c_shared_controller_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
+	int num)
+{
+	struct dw_i2c_dev *dev = i2c_get_adapdata(adap);
+	int err;
+
+	if (dev->shared_host) {
+		err = dev->acquire_ownership(dev->dev);
+		if (!err) {
+			err = i2c_dw_xfer(adap, msgs, num);
+			dev->release_ownership(dev->dev);
+		} else
+			dev_WARN(dev->dev, "couldnt acquire ownership\n");
+
+		return err;
+	} else
+		return i2c_dw_xfer(adap, msgs, num);
+}
+
+static struct i2c_algorithm i2c_sc_algo = {
+	.master_xfer	= i2c_shared_controller_xfer,
+	.functionality	= i2c_dw_func,
+};
+#endif
+
 #ifdef CONFIG_ACPI
 static void dw_i2c_acpi_params(struct platform_device *pdev, char method[],
 			       u16 *hcnt, u16 *lcnt, u32 *sda_hold)
@@ -80,8 +106,11 @@ static int dw_i2c_acpi_configure(struct platform_device *pdev)
 {
 	struct dw_i2c_dev *dev = platform_get_drvdata(pdev);
 	bool fs_mode = dev->master_cfg & DW_IC_CON_SPEED_FAST;
+	acpi_handle handle = ACPI_HANDLE(&pdev->dev);
+	acpi_status status;
+	unsigned long long shared_host = 0;
 
-	if (!ACPI_HANDLE(&pdev->dev))
+	if (!handle)
 		return -ENODEV;
 
 	dev->adapter.nr = -1;
@@ -97,6 +126,24 @@ static int dw_i2c_acpi_configure(struct platform_device *pdev)
 	dw_i2c_acpi_params(pdev, "FMCN", &dev->fs_hcnt, &dev->fs_lcnt,
 			   fs_mode ? &dev->sda_hold_time : NULL);
 
+#if IS_ENABLED(CONFIG_I2C_SHARED_CONTROLLER)
+	/*
+	 * For Intel SOC's determine if i2c bus must be shared with PUNIT
+	 * hardware
+	 */
+	status = acpi_evaluate_integer(handle, "_SEM", NULL, &shared_host);
+
+	if (ACPI_SUCCESS(status))
+		dev_info(&pdev->dev, "_SEM=%ld\n", (long)shared_host);
+
+	if (shared_host != 0) {
+		dev_info(&pdev->dev,
+			"Host shares controller with other hardware\n");
+		dev->shared_host = 1;
+		dev->acquire_ownership = i2c_acquire_ownership;
+		dev->release_ownership = i2c_release_ownership;
+	}
+#endif /* CONFIG_I2C_SHARED_CONTROLLER */
 	return 0;
 }
 
@@ -115,7 +162,7 @@ static inline int dw_i2c_acpi_configure(struct platform_device *pdev)
 {
 	return -ENODEV;
 }
-#endif
+#endif /* CONFIG_ACPI */
 
 static int dw_i2c_probe(struct platform_device *pdev)
 {
@@ -212,6 +259,25 @@ static int dw_i2c_probe(struct platform_device *pdev)
 	adap->dev.parent = &pdev->dev;
 	adap->dev.of_node = pdev->dev.of_node;
 
+#if IS_ENABLED(CONFIG_I2C_SHARED_CONTROLLER)
+	if (dev->shared_host)
+		adap->algo = &i2c_sc_algo;
+
+	r = i2c_add_numbered_adapter(adap);
+	if (r) {
+		dev_err(&pdev->dev, "failure adding adapter\n");
+		return r;
+	}
+
+	if (dev->shared_host)
+		pm_runtime_forbid(&pdev->dev);
+	else {
+		pm_runtime_set_autosuspend_delay(&pdev->dev, 1000);
+		pm_runtime_use_autosuspend(&pdev->dev);
+		pm_runtime_set_active(&pdev->dev);
+		pm_runtime_enable(&pdev->dev);
+	}
+#else
 	r = i2c_add_numbered_adapter(adap);
 	if (r) {
 		dev_err(&pdev->dev, "failure adding adapter\n");
@@ -222,7 +288,7 @@ static int dw_i2c_probe(struct platform_device *pdev)
 	pm_runtime_use_autosuspend(&pdev->dev);
 	pm_runtime_set_active(&pdev->dev);
 	pm_runtime_enable(&pdev->dev);
-
+#endif
 	return 0;
 }
 
@@ -268,7 +334,11 @@ static int dw_i2c_resume(struct device *dev)
 	struct dw_i2c_dev *i_dev = platform_get_drvdata(pdev);
 
 	clk_prepare_enable(i_dev->clk);
-	i2c_dw_init(i_dev);
+
+#if IS_ENABLED(CONFIG_I2C_SHARED_CONTROLLER)
+	if (!i_dev->shared_host)
+#endif
+		i2c_dw_init(i_dev);
 
 	return 0;
 }
diff --git a/drivers/i2c/busses/i2c-shared-controller.c b/drivers/i2c/busses/i2c-shared-controller.c
new file mode 100644
index 0000000..b9119a0
--- /dev/null
+++ b/drivers/i2c/busses/i2c-shared-controller.c
@@ -0,0 +1,101 @@
+/*
+ * Intel SOC I2C bus sharing semphore implementation
+ * 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 <asm/iosf_mbi.h>
+
+#define PUNIT_SEMAPHORE 0x7
+static unsigned long start_time, end_time;
+
+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_WARN(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\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\n");
+}
+
+int i2c_acquire_ownership(struct device *dev)
+{
+	u32 sem = 0;
+	int ret;
+	int timeout = 100;
+
+	/* 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_WARN(dev, "iosf failed to request punit semaphore\n");
+		return ret;
+	}
+
+	/* host driver waits for bit 0 to be set in semaphore register */
+	while (1) {
+		ret = get_sem(dev, &sem);
+		if (!ret && sem) {
+			start_time = jiffies;
+			dev_dbg(dev, "punit semaphore acquired after %d attempts\n",
+				101 - timeout);
+			return 0;
+		}
+
+		usleep_range(1000, 2000);
+		timeout--;
+		if (timeout <= 0) {
+			dev_err(dev, "punit semaphore timed out, resetting\n");
+			reset_semaphore(dev);
+			iosf_mbi_read(BT_MBI_UNIT_PMC, BT_MBI_BUNIT_READ,
+				PUNIT_SEMAPHORE, &sem);
+			dev_err(dev, "PUNIT SEM: %d\n", sem);
+			WARN_ON(1);
+			return -ETIMEDOUT;
+		}
+
+	}
+}
+
+int i2c_release_ownership(struct device *dev)
+{
+	reset_semaphore(dev);
+	end_time = jiffies;
+	dev_dbg(dev, "punit semaphore release call finish, held for %ldms\n",
+		(end_time - start_time) * 1000 / HZ);
+	return 0;
+}
-- 
1.9.1

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