diff mbox series

[v2,1/3] x86: baytrail/cherrytrail: Rework and move P-Unit PMIC bus semaphore code

Message ID 20181011102627.7418-2-hdegoede@redhat.com
State Superseded
Headers show
Series x86: baytrail/cherrytrail: Rework and move P-Unit PMIC semaphore handling | expand

Commit Message

Hans de Goede Oct. 11, 2018, 10:26 a.m. UTC 
On some BYT/CHT systems the SoC's P-Unit shares the I2C bus with the
kernel. The P-Unit has a semaphore for the PMIC bus which we can take to
block it from accessing the shared bus while the kernel wants to access it.

Currently we have the I2C-controller driver acquiring and releasing the
semaphore around each I2C transfer. There are 2 problems with this:

1) PMIC accesses often come in the form of a read-modify-write on one of
the PMIC registers, we currently release the P-Unit's PMIC bus semaphore
between the read and the write. If the P-Unit modifies the register during
this window?, then we end up overwriting the P-Unit's changes.
I believe that this is mostly an academic problem, but I'm not sure.

2) To safely access the shared I2C bus, we need to do 3 things:
a) Notify the GPU driver that we are starting a window in which it may not
access the P-Unit, since the P-Unit seems to ignore the semaphore for
explicit power-level requests made by the GPU driver
b) Make a pm_qos request to force all CPU cores out of C6/C7 since entering
C6/C7 while we hold the semaphore hangs the SoC
c) Finally take the P-Unit's PMIC bus semaphore
All 3 these steps together are somewhat expensive, so ideally if we have
a bunch of i2c transfers grouped together we only do this once for the
entire group.

Taking the read-modify-write on a PMIC register as example then ideally we
would only do all 3 steps once at the beginning and undo all 3 steps once
at the end.

For this we need to be able to take the semaphore from within e.g. the PMIC
opregion driver, yet we do not want to remove the taking of the semaphore
from the I2C-controller driver, as that is still necessary to protect many
other code-paths leading to accessing the shared I2C bus.

This means that we first have the PMIC driver acquire the semaphore and
then have the I2C controller driver trying to acquire it again.

To make this possible this commit does the following:

1) Move the semaphore code from being private to the I2C controller driver
into the generic iosf_mbi code, which already has other code to deal with
the shared bus so that it can be accessed outside of the I2C bus driver.

2) Rework the code so that it can be called multiple times nested, while
still blocking I2C accesses while e.g. the GPU driver has indicated the
P-Unit needs the bus through a iosf_mbi_punit_acquire() call.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
Note this commit deliberately limits the i2c-designware changes to
only touch i2c-designware-baytrail.c, deliberately not doing some cleanups
which become possible after removing the semaphore code from the
i2c-designmware code. This is done so that this commit can be merged
through the x86 tree without causing conflicts in the i2c tree.

The cleanups to the i2c-designware tree will be done in a follow up
patch which can be merged once this commit is in place.
---
Changes in v2:
-Move mutex_unlock(&iosf_mbi_punit_mutex); to the callers of
 iosf_mbi_reset_semaphore()
-Use PCI_DEVICE_DATA() to pass the driver_data
---
 arch/x86/include/asm/iosf_mbi.h              |  39 ++--
 arch/x86/platform/intel/iosf_mbi.c           | 176 +++++++++++++++++--
 drivers/i2c/busses/i2c-designware-baytrail.c | 125 +------------
 3 files changed, 189 insertions(+), 151 deletions(-)

Comments

Ingo Molnar Oct. 11, 2018, 10:41 a.m. UTC | #1 
* Hans de Goede <hdegoede@redhat.com> wrote:

> +int iosf_mbi_block_punit_i2c_access(void)
> +{
> +	unsigned long start, end;
> +	int ret = 0;
> +	u32 sem;
> +
> +	if (WARN_ON(!mbi_pdev || !iosf_mbi_sem_address))
> +		return -ENXIO;
> +
> +	mutex_lock(&iosf_mbi_block_punit_i2c_access_count_mutex);
> +
> +	if (iosf_mbi_block_punit_i2c_access_count > 0)
> +		goto out;
> +
> +	mutex_lock(&iosf_mbi_punit_mutex);
> +	blocking_notifier_call_chain(&iosf_mbi_pmic_bus_access_notifier,
> +				     MBI_PMIC_BUS_ACCESS_BEGIN, NULL);
> +
> +	/*
> +	 * Disallow the CPU to enter C6 or C7 state, entering these states
> +	 * requires the punit to talk to the pmic and if this happens while
> +	 * we're holding the semaphore, the SoC hangs.
> +	 */
> +	pm_qos_update_request(&iosf_mbi_pm_qos, 0);
> +
> +	/* host driver writes to side band semaphore register */
> +	ret = iosf_mbi_write(BT_MBI_UNIT_PMC, MBI_REG_WRITE,
> +			     iosf_mbi_sem_address, PUNIT_SEMAPHORE_ACQUIRE);
> +	if (ret) {
> +		dev_err(&mbi_pdev->dev, "Error punit semaphore request failed\n");
> +		goto out;
> +	}

Isn't this error path leaking the iosf_mbi_punit_mutex held mutex? The 'out' label only unlocks 
iosf_mbi_block_punit_i2c_access_count_mutex:


> +	/* host driver waits for bit 0 to be set in semaphore register */
> +	start = jiffies;
> +	end = start + msecs_to_jiffies(SEMAPHORE_TIMEOUT);
> +	do {
> +		ret = iosf_mbi_get_sem(&sem);
> +		if (!ret && sem) {
> +			iosf_mbi_sem_acquired = jiffies;
> +			dev_dbg(&mbi_pdev->dev, "punit semaphore acquired after %ums\n",
> +				jiffies_to_msecs(jiffies - start));
> +			/*
> +			 * Success, keep iosf_mbi_punit_mutex locked till
> +			 * iosf_mbi_unblock_punit_i2c_access() gets called.
> +			 */
> +			goto out;

Ditto - although this does claim that this is done intentionally.

> +		}
> +
> +		usleep_range(1000, 2000);
> +	} while (time_before(jiffies, end));
> +
> +	ret = -ETIMEDOUT;
> +	dev_err(&mbi_pdev->dev, "Error punit semaphore timed out, resetting\n");
> +	iosf_mbi_reset_semaphore();
> +	mutex_unlock(&iosf_mbi_punit_mutex);
> +
> +	if (!iosf_mbi_get_sem(&sem))
> +		dev_err(&mbi_pdev->dev, "PUNIT SEM: %d\n", sem);
> +out:
> +	if (!WARN_ON(ret))
> +		iosf_mbi_block_punit_i2c_access_count++;
> +
> +	mutex_unlock(&iosf_mbi_block_punit_i2c_access_count_mutex);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(iosf_mbi_block_punit_i2c_access);

So this is a rather unusual looking locking pattern.

So if this is all intended and works fine then at minimum the semantics of the function should 
be explained - right now it has no description whatsoever.

Thanks,

	Ingo
Hans de Goede Oct. 11, 2018, 11:58 a.m. UTC | #2 
Hi,

On 11-10-18 12:41, Ingo Molnar wrote:
> 
> * Hans de Goede <hdegoede@redhat.com> wrote:
> 
>> +int iosf_mbi_block_punit_i2c_access(void)
>> +{
>> +	unsigned long start, end;
>> +	int ret = 0;
>> +	u32 sem;
>> +
>> +	if (WARN_ON(!mbi_pdev || !iosf_mbi_sem_address))
>> +		return -ENXIO;
>> +
>> +	mutex_lock(&iosf_mbi_block_punit_i2c_access_count_mutex);
>> +
>> +	if (iosf_mbi_block_punit_i2c_access_count > 0)
>> +		goto out;
>> +
>> +	mutex_lock(&iosf_mbi_punit_mutex);
>> +	blocking_notifier_call_chain(&iosf_mbi_pmic_bus_access_notifier,
>> +				     MBI_PMIC_BUS_ACCESS_BEGIN, NULL);
>> +
>> +	/*
>> +	 * Disallow the CPU to enter C6 or C7 state, entering these states
>> +	 * requires the punit to talk to the pmic and if this happens while
>> +	 * we're holding the semaphore, the SoC hangs.
>> +	 */
>> +	pm_qos_update_request(&iosf_mbi_pm_qos, 0);
>> +
>> +	/* host driver writes to side band semaphore register */
>> +	ret = iosf_mbi_write(BT_MBI_UNIT_PMC, MBI_REG_WRITE,
>> +			     iosf_mbi_sem_address, PUNIT_SEMAPHORE_ACQUIRE);
>> +	if (ret) {
>> +		dev_err(&mbi_pdev->dev, "Error punit semaphore request failed\n");
>> +		goto out;
>> +	}
> 
> Isn't this error path leaking the iosf_mbi_punit_mutex held mutex? The 'out' label only unlocks
> iosf_mbi_block_punit_i2c_access_count_mutex:

Yes you're right, I messed this up when adding the handling for the new
iosf_mbi_block_punit_i2c_access_count[_mutex] which is new compared to the
code from i2c-designware-baytrail.c (the rest of the code is just moved
from there).

This is fixed in the upcoming v3 of the patch.

>> +	/* host driver waits for bit 0 to be set in semaphore register */
>> +	start = jiffies;
>> +	end = start + msecs_to_jiffies(SEMAPHORE_TIMEOUT);
>> +	do {
>> +		ret = iosf_mbi_get_sem(&sem);
>> +		if (!ret && sem) {
>> +			iosf_mbi_sem_acquired = jiffies;
>> +			dev_dbg(&mbi_pdev->dev, "punit semaphore acquired after %ums\n",
>> +				jiffies_to_msecs(jiffies - start));
>> +			/*
>> +			 * Success, keep iosf_mbi_punit_mutex locked till
>> +			 * iosf_mbi_unblock_punit_i2c_access() gets called.
>> +			 */
>> +			goto out;
> 
> Ditto - although this does claim that this is done intentionally.

Right, we have 2 sets of functions:

iosf_mbi_punit_acquire()
iosf_mbi_punit_release()

iosf_mbi_block_punit_i2c_access()
iosf_mbi_unblock_punit_i2c_access()

The first 2 are for code which sends request to the P-Unit
which may make it access the shared I2C bus to the PMIC, calling
these will stop any kernel I2C code from accessing the bus.

The latter 2 are for I2C code which wants to access the
shared I2C bus to the PMIC, such as e.g. the fuel-gauge driver,
these block any callers of iosf_mbi_punit_acquire() from
continuing until iosf_mbi_unblock_punit_i2c_access() gets
called.

Basically we have 2 groups of code trying to access the same
shared resource (the PMIC I2C bus), code talking to the P-Unit
(which has its own access to the I2C bus at some level) and
I2C client drivers (or ACPI OpRegions).

If both happen at the same time bad things happen, so we
need to arbitrate and exclusively allow accesses of one kind
at a time. This is implemetned by both type of accesses acquiring
the iosf_mbi_punit_mutex and keeping it locked over the access,
hence the exit from the function keeps the mutex locked on success.

>> +		}
>> +
>> +		usleep_range(1000, 2000);
>> +	} while (time_before(jiffies, end));
>> +
>> +	ret = -ETIMEDOUT;
>> +	dev_err(&mbi_pdev->dev, "Error punit semaphore timed out, resetting\n");
>> +	iosf_mbi_reset_semaphore();
>> +	mutex_unlock(&iosf_mbi_punit_mutex);
>> +
>> +	if (!iosf_mbi_get_sem(&sem))
>> +		dev_err(&mbi_pdev->dev, "PUNIT SEM: %d\n", sem);
>> +out:
>> +	if (!WARN_ON(ret))
>> +		iosf_mbi_block_punit_i2c_access_count++;
>> +
>> +	mutex_unlock(&iosf_mbi_block_punit_i2c_access_count_mutex);
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL(iosf_mbi_block_punit_i2c_access);
> 
> So this is a rather unusual looking locking pattern.
> 
> So if this is all intended and works fine then at minimum the semantics of the function should
> be explained - right now it has no description whatsoever.

Ok, for v3 I've added the following comment above the new
iosf_mbi_block_punit_i2c_access() to explain things:

/*
  * This function blocks P-Unit accesses to the PMIC I2C bus, so that kernel
  * I2C code, such as e.g. a fuel-gauge driver, can access it safely.
  *
  * This function may be called by I2C controller code while an I2C driver has
  * already blocked P-Unit accesses because it wants them blocked over multiple
  * i2c-transfers, for e.g. read-modify-write of an I2C client register.
  *
  * The P-Unit accesses already being blocked is tracked through the
  * iosf_mbi_block_punit_i2c_access_count variable which is protected by the
  * iosf_mbi_block_punit_i2c_access_count_mutex this mutex is hold for the
  * entire duration of the function.
  *
  * If access is not blocked yet, this function takes the following steps:
  *
  * 1) Some code sends request to the P-Unit which make it access the PMIC
  *    I2C bus. Testing has shown that the P-Unit does not check its internal
  *    PMIC bus semaphore for these requests. Callers of these requests call
  *    iosf_mbi_punit_acquire()/_release() around their P-Unit accesses, these
  *    functions lock/unlock the iosf_mbi_punit_mutex.
  *    As the first step we lock the iosf_mbi_punit_mutex, to wait for any in
  *    flight requests to finish and to block any new requests.
  *
  * 2) Some code makes such P-Unit requests from atomic contexts where it
  *    cannot call iosf_mbi_punit_acquire() as that may sleep.
  *    As the second step we call a notifier chain which allows any code
  *    needing P-Unit resources from atomic context to acquire them before
  *    we take control over the PMIC I2C bus.
  *
  * 3) When CPU cores enter C6 or C7 the P-Unit needs to talk to the PMIC
  *    if this happens while the kernel itself is accessing the PMIC I2C bus
  *    the SoC hangs.
  *    As the third step we call pm_qos_update_request() to disallow the CPU
  *    to enter C6 or C7.
  *
  * 4) The P-Unit has a PMIC bus semaphore which we can request to stop
  *    autonomous P-Unit tasks from accessing the PMIC I2C bus while we hold it.
  *    As the fourth and final step we request this semaphore and wait for our
  *    request to be acknowledged.
  */

Regards,

Hans
diff mbox series

Patch

diff --git a/arch/x86/include/asm/iosf_mbi.h b/arch/x86/include/asm/iosf_mbi.h
index 3de0489deade..5270ff39b9af 100644
--- a/arch/x86/include/asm/iosf_mbi.h
+++ b/arch/x86/include/asm/iosf_mbi.h
@@ -105,8 +105,10 @@  int iosf_mbi_modify(u8 port, u8 opcode, u32 offset, u32 mdr, u32 mask);
  * the PMIC bus while another driver is also accessing the PMIC bus various bad
  * things happen.
  *
- * To avoid these problems this function must be called before accessing the
- * P-Unit or the PMIC, be it through iosf_mbi* functions or through other means.
+ * Call this function before sending requests to the P-Unit which may make it
+ * access the PMIC, be it through iosf_mbi* functions or through other means.
+ * This function will block all kernel access to the PMIC I2C bus, so that the
+ * P-Unit can safely access the PMIC over the shared I2C bus.
  *
  * Note on these systems the i2c-bus driver will request a sempahore from the
  * P-Unit for exclusive access to the PMIC bus when i2c drivers are accessing
@@ -122,6 +124,31 @@  void iosf_mbi_punit_acquire(void);
  */
 void iosf_mbi_punit_release(void);
 
+/**
+ * iosf_mbi_block_punit_i2c_access() - Block P-Unit accesses to the PMIC bus
+ *
+ * Call this function to block P-Unit access to the PMIC I2C bus, so that the
+ * kernel can safely access the PMIC over the shared I2C bus.
+ *
+ * This function acquires the P-Unit bus semaphore and notifies
+ * pmic_bus_access_notifier listeners that they may no longer access the
+ * P-Unit in a way which may cause it to access the shared I2C bus.
+ *
+ * Note this function may be called multiple times and the bus will not
+ * be released until iosf_mbi_unblock_punit_i2c_access() has been called the
+ * same amount of times.
+ *
+ * Return: Nonzero on error
+ */
+int iosf_mbi_block_punit_i2c_access(void);
+
+/*
+ * iosf_mbi_unblock_punit_i2c_access() - Release PMIC I2C bus block
+ *
+ * Release i2c access block gotten through iosf_mbi_block_punit_i2c_access().
+ */
+void iosf_mbi_unblock_punit_i2c_access(void);
+
 /**
  * iosf_mbi_register_pmic_bus_access_notifier - Register PMIC bus notifier
  *
@@ -158,14 +185,6 @@  int iosf_mbi_unregister_pmic_bus_access_notifier(struct notifier_block *nb);
 int iosf_mbi_unregister_pmic_bus_access_notifier_unlocked(
 	struct notifier_block *nb);
 
-/**
- * iosf_mbi_call_pmic_bus_access_notifier_chain - Call PMIC bus notifier chain
- *
- * @val: action to pass into listener's notifier_call function
- * @v: data pointer to pass into listener's notifier_call function
- */
-int iosf_mbi_call_pmic_bus_access_notifier_chain(unsigned long val, void *v);
-
 /**
  * iosf_mbi_assert_punit_acquired - Assert that the P-Unit has been acquired.
  */
diff --git a/arch/x86/platform/intel/iosf_mbi.c b/arch/x86/platform/intel/iosf_mbi.c
index 6f37a2137a79..eb58cbf6da18 100644
--- a/arch/x86/platform/intel/iosf_mbi.c
+++ b/arch/x86/platform/intel/iosf_mbi.c
@@ -18,24 +18,26 @@ 
  * enumerate the device using PCI.
  */
 
+#include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/spinlock.h>
 #include <linux/pci.h>
 #include <linux/debugfs.h>
 #include <linux/capability.h>
+#include <linux/pm_qos.h>
 
 #include <asm/iosf_mbi.h>
 
-#define PCI_DEVICE_ID_BAYTRAIL		0x0F00
-#define PCI_DEVICE_ID_BRASWELL		0x2280
-#define PCI_DEVICE_ID_QUARK_X1000	0x0958
-#define PCI_DEVICE_ID_TANGIER		0x1170
+#define PCI_DEVICE_ID_INTEL_BAYTRAIL		0x0F00
+#define PCI_DEVICE_ID_INTEL_BRASWELL		0x2280
+#define PCI_DEVICE_ID_INTEL_QUARK_X1000		0x0958
+#define PCI_DEVICE_ID_INTEL_TANGIER		0x1170
 
 static struct pci_dev *mbi_pdev;
 static DEFINE_SPINLOCK(iosf_mbi_lock);
-static DEFINE_MUTEX(iosf_mbi_punit_mutex);
-static BLOCKING_NOTIFIER_HEAD(iosf_mbi_pmic_bus_access_notifier);
+
+/**************** Generic iosf_mbi access helpers ****************/
 
 static inline u32 iosf_mbi_form_mcr(u8 op, u8 port, u8 offset)
 {
@@ -192,6 +194,30 @@  bool iosf_mbi_available(void)
 }
 EXPORT_SYMBOL(iosf_mbi_available);
 
+/*
+ **************** PUNIT/kernel shared i2c bus arbritration ****************
+ *
+ * Some Bay Trail and Cherry Trail devices have the PUNIT and us (the kernel)
+ * share a single I2C bus to the PMIC. Below are helpers to arbitrate the
+ * accesses between the kernel and the PUNIT.
+ *
+ * See arch/x86/include/asm/iosf_mbi.h for kernel-doc text for each function.
+ */
+
+#define SEMAPHORE_TIMEOUT		500
+#define PUNIT_SEMAPHORE_BYT		0x7
+#define PUNIT_SEMAPHORE_CHT		0x10e
+#define PUNIT_SEMAPHORE_BIT		BIT(0)
+#define PUNIT_SEMAPHORE_ACQUIRE		BIT(1)
+
+static DEFINE_MUTEX(iosf_mbi_punit_mutex);
+static DEFINE_MUTEX(iosf_mbi_block_punit_i2c_access_count_mutex);
+static BLOCKING_NOTIFIER_HEAD(iosf_mbi_pmic_bus_access_notifier);
+static u32 iosf_mbi_block_punit_i2c_access_count;
+static u32 iosf_mbi_sem_address;
+static unsigned long iosf_mbi_sem_acquired;
+static struct pm_qos_request iosf_mbi_pm_qos;
+
 void iosf_mbi_punit_acquire(void)
 {
 	mutex_lock(&iosf_mbi_punit_mutex);
@@ -204,6 +230,118 @@  void iosf_mbi_punit_release(void)
 }
 EXPORT_SYMBOL(iosf_mbi_punit_release);
 
+static int iosf_mbi_get_sem(u32 *sem)
+{
+	int ret;
+
+	ret = iosf_mbi_read(BT_MBI_UNIT_PMC, MBI_REG_READ,
+			    iosf_mbi_sem_address, sem);
+	if (ret) {
+		dev_err(&mbi_pdev->dev, "Error punit semaphore read failed\n");
+		return ret;
+	}
+
+	*sem &= PUNIT_SEMAPHORE_BIT;
+	return 0;
+}
+
+static void iosf_mbi_reset_semaphore(void)
+{
+	if (iosf_mbi_modify(BT_MBI_UNIT_PMC, MBI_REG_READ,
+			    iosf_mbi_sem_address, 0, PUNIT_SEMAPHORE_BIT))
+		dev_err(&mbi_pdev->dev, "Error punit semaphore reset failed\n");
+
+	pm_qos_update_request(&iosf_mbi_pm_qos, PM_QOS_DEFAULT_VALUE);
+
+	blocking_notifier_call_chain(&iosf_mbi_pmic_bus_access_notifier,
+				     MBI_PMIC_BUS_ACCESS_END, NULL);
+}
+
+int iosf_mbi_block_punit_i2c_access(void)
+{
+	unsigned long start, end;
+	int ret = 0;
+	u32 sem;
+
+	if (WARN_ON(!mbi_pdev || !iosf_mbi_sem_address))
+		return -ENXIO;
+
+	mutex_lock(&iosf_mbi_block_punit_i2c_access_count_mutex);
+
+	if (iosf_mbi_block_punit_i2c_access_count > 0)
+		goto out;
+
+	mutex_lock(&iosf_mbi_punit_mutex);
+	blocking_notifier_call_chain(&iosf_mbi_pmic_bus_access_notifier,
+				     MBI_PMIC_BUS_ACCESS_BEGIN, NULL);
+
+	/*
+	 * Disallow the CPU to enter C6 or C7 state, entering these states
+	 * requires the punit to talk to the pmic and if this happens while
+	 * we're holding the semaphore, the SoC hangs.
+	 */
+	pm_qos_update_request(&iosf_mbi_pm_qos, 0);
+
+	/* host driver writes to side band semaphore register */
+	ret = iosf_mbi_write(BT_MBI_UNIT_PMC, MBI_REG_WRITE,
+			     iosf_mbi_sem_address, PUNIT_SEMAPHORE_ACQUIRE);
+	if (ret) {
+		dev_err(&mbi_pdev->dev, "Error punit semaphore request failed\n");
+		goto out;
+	}
+
+	/* host driver waits for bit 0 to be set in semaphore register */
+	start = jiffies;
+	end = start + msecs_to_jiffies(SEMAPHORE_TIMEOUT);
+	do {
+		ret = iosf_mbi_get_sem(&sem);
+		if (!ret && sem) {
+			iosf_mbi_sem_acquired = jiffies;
+			dev_dbg(&mbi_pdev->dev, "punit semaphore acquired after %ums\n",
+				jiffies_to_msecs(jiffies - start));
+			/*
+			 * Success, keep iosf_mbi_punit_mutex locked till
+			 * iosf_mbi_unblock_punit_i2c_access() gets called.
+			 */
+			goto out;
+		}
+
+		usleep_range(1000, 2000);
+	} while (time_before(jiffies, end));
+
+	ret = -ETIMEDOUT;
+	dev_err(&mbi_pdev->dev, "Error punit semaphore timed out, resetting\n");
+	iosf_mbi_reset_semaphore();
+	mutex_unlock(&iosf_mbi_punit_mutex);
+
+	if (!iosf_mbi_get_sem(&sem))
+		dev_err(&mbi_pdev->dev, "PUNIT SEM: %d\n", sem);
+out:
+	if (!WARN_ON(ret))
+		iosf_mbi_block_punit_i2c_access_count++;
+
+	mutex_unlock(&iosf_mbi_block_punit_i2c_access_count_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL(iosf_mbi_block_punit_i2c_access);
+
+void iosf_mbi_unblock_punit_i2c_access(void)
+{
+	mutex_lock(&iosf_mbi_block_punit_i2c_access_count_mutex);
+
+	iosf_mbi_block_punit_i2c_access_count--;
+	if (iosf_mbi_block_punit_i2c_access_count == 0) {
+		iosf_mbi_reset_semaphore();
+		mutex_unlock(&iosf_mbi_punit_mutex);
+		dev_dbg(&mbi_pdev->dev, "punit semaphore held for %ums\n",
+			jiffies_to_msecs(jiffies - iosf_mbi_sem_acquired));
+	}
+
+	mutex_unlock(&iosf_mbi_block_punit_i2c_access_count_mutex);
+}
+EXPORT_SYMBOL(iosf_mbi_unblock_punit_i2c_access);
+
 int iosf_mbi_register_pmic_bus_access_notifier(struct notifier_block *nb)
 {
 	int ret;
@@ -241,19 +379,14 @@  int iosf_mbi_unregister_pmic_bus_access_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL(iosf_mbi_unregister_pmic_bus_access_notifier);
 
-int iosf_mbi_call_pmic_bus_access_notifier_chain(unsigned long val, void *v)
-{
-	return blocking_notifier_call_chain(
-				&iosf_mbi_pmic_bus_access_notifier, val, v);
-}
-EXPORT_SYMBOL(iosf_mbi_call_pmic_bus_access_notifier_chain);
-
 void iosf_mbi_assert_punit_acquired(void)
 {
 	WARN_ON(!mutex_is_locked(&iosf_mbi_punit_mutex));
 }
 EXPORT_SYMBOL(iosf_mbi_assert_punit_acquired);
 
+/**************** iosf_mbi debug code ****************/
+
 #ifdef CONFIG_IOSF_MBI_DEBUG
 static u32	dbg_mdr;
 static u32	dbg_mcr;
@@ -338,7 +471,7 @@  static inline void iosf_debugfs_remove(void) { }
 #endif /* CONFIG_IOSF_MBI_DEBUG */
 
 static int iosf_mbi_probe(struct pci_dev *pdev,
-			  const struct pci_device_id *unused)
+			  const struct pci_device_id *dev_id)
 {
 	int ret;
 
@@ -349,14 +482,16 @@  static int iosf_mbi_probe(struct pci_dev *pdev,
 	}
 
 	mbi_pdev = pci_dev_get(pdev);
+	iosf_mbi_sem_address = dev_id->driver_data;
+
 	return 0;
 }
 
 static const struct pci_device_id iosf_mbi_pci_ids[] = {
-	{ PCI_DEVICE(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_BAYTRAIL) },
-	{ PCI_DEVICE(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_BRASWELL) },
-	{ PCI_DEVICE(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_QUARK_X1000) },
-	{ PCI_DEVICE(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_TANGIER) },
+	{ PCI_DEVICE_DATA(INTEL, BAYTRAIL, PUNIT_SEMAPHORE_BYT) },
+	{ PCI_DEVICE_DATA(INTEL, BRASWELL, PUNIT_SEMAPHORE_CHT) },
+	{ PCI_DEVICE_DATA(INTEL, QUARK_X1000, 0) },
+	{ PCI_DEVICE_DATA(INTEL, TANGIER, 0) },
 	{ 0, },
 };
 MODULE_DEVICE_TABLE(pci, iosf_mbi_pci_ids);
@@ -371,6 +506,9 @@  static int __init iosf_mbi_init(void)
 {
 	iosf_debugfs_init();
 
+	pm_qos_add_request(&iosf_mbi_pm_qos, PM_QOS_CPU_DMA_LATENCY,
+			   PM_QOS_DEFAULT_VALUE);
+
 	return pci_register_driver(&iosf_mbi_pci_driver);
 }
 
@@ -381,6 +519,8 @@  static void __exit iosf_mbi_exit(void)
 	pci_unregister_driver(&iosf_mbi_pci_driver);
 	pci_dev_put(mbi_pdev);
 	mbi_pdev = NULL;
+
+	pm_qos_remove_request(&iosf_mbi_pm_qos);
 }
 
 module_init(iosf_mbi_init);
diff --git a/drivers/i2c/busses/i2c-designware-baytrail.c b/drivers/i2c/busses/i2c-designware-baytrail.c
index 9ca1feaba98f..8c84fa0b0384 100644
--- a/drivers/i2c/busses/i2c-designware-baytrail.c
+++ b/drivers/i2c/busses/i2c-designware-baytrail.c
@@ -3,139 +3,23 @@ 
  * Intel BayTrail PMIC I2C bus semaphore implementaion
  * Copyright (c) 2014, Intel Corporation.
  */
-#include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/acpi.h>
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
-#include <linux/pm_qos.h>
 
 #include <asm/iosf_mbi.h>
 
 #include "i2c-designware-core.h"
 
-#define SEMAPHORE_TIMEOUT	500
-#define PUNIT_SEMAPHORE		0x7
-#define PUNIT_SEMAPHORE_CHT	0x10e
-#define PUNIT_SEMAPHORE_BIT	BIT(0)
-#define PUNIT_SEMAPHORE_ACQUIRE	BIT(1)
-
-static unsigned long acquired;
-
-static u32 get_sem_addr(struct dw_i2c_dev *dev)
-{
-	if (dev->flags & MODEL_CHERRYTRAIL)
-		return PUNIT_SEMAPHORE_CHT;
-	else
-		return PUNIT_SEMAPHORE;
-}
-
-static int get_sem(struct dw_i2c_dev *dev, u32 *sem)
-{
-	u32 addr = get_sem_addr(dev);
-	u32 data;
-	int ret;
-
-	ret = iosf_mbi_read(BT_MBI_UNIT_PMC, MBI_REG_READ, addr, &data);
-	if (ret) {
-		dev_err(dev->dev, "iosf failed to read punit semaphore\n");
-		return ret;
-	}
-
-	*sem = data & PUNIT_SEMAPHORE_BIT;
-
-	return 0;
-}
-
-static void reset_semaphore(struct dw_i2c_dev *dev)
-{
-	if (iosf_mbi_modify(BT_MBI_UNIT_PMC, MBI_REG_READ, get_sem_addr(dev),
-			    0, PUNIT_SEMAPHORE_BIT))
-		dev_err(dev->dev, "iosf failed to reset punit semaphore during write\n");
-
-	pm_qos_update_request(&dev->pm_qos, PM_QOS_DEFAULT_VALUE);
-
-	iosf_mbi_call_pmic_bus_access_notifier_chain(MBI_PMIC_BUS_ACCESS_END,
-						     NULL);
-	iosf_mbi_punit_release();
-}
-
 static int baytrail_i2c_acquire(struct dw_i2c_dev *dev)
 {
-	u32 addr;
-	u32 sem = PUNIT_SEMAPHORE_ACQUIRE;
-	int ret;
-	unsigned long start, end;
-
-	might_sleep();
-
-	if (!dev || !dev->dev)
-		return -ENODEV;
-
-	if (!dev->release_lock)
-		return 0;
-
-	iosf_mbi_punit_acquire();
-	iosf_mbi_call_pmic_bus_access_notifier_chain(MBI_PMIC_BUS_ACCESS_BEGIN,
-						     NULL);
-
-	/*
-	 * Disallow the CPU to enter C6 or C7 state, entering these states
-	 * requires the punit to talk to the pmic and if this happens while
-	 * we're holding the semaphore, the SoC hangs.
-	 */
-	pm_qos_update_request(&dev->pm_qos, 0);
-
-	addr = get_sem_addr(dev);
-
-	/* host driver writes to side band semaphore register */
-	ret = iosf_mbi_write(BT_MBI_UNIT_PMC, MBI_REG_WRITE, addr, sem);
-	if (ret) {
-		dev_err(dev->dev, "iosf punit semaphore request failed\n");
-		goto out;
-	}
-
-	/* host driver waits for bit 0 to be set in semaphore register */
-	start = jiffies;
-	end = start + msecs_to_jiffies(SEMAPHORE_TIMEOUT);
-	do {
-		ret = get_sem(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);
-	} while (time_before(jiffies, end));
-
-	dev_err(dev->dev, "punit semaphore timed out, resetting\n");
-out:
-	reset_semaphore(dev);
-
-	ret = iosf_mbi_read(BT_MBI_UNIT_PMC, MBI_REG_READ, addr, &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;
+	return iosf_mbi_block_punit_i2c_access();
 }
 
 static void baytrail_i2c_release(struct dw_i2c_dev *dev)
 {
-	if (!dev || !dev->dev)
-		return;
-
-	if (!dev->acquire_lock)
-		return;
-
-	reset_semaphore(dev);
-	dev_dbg(dev->dev, "punit semaphore held for %ums\n",
-		jiffies_to_msecs(jiffies - acquired));
+	iosf_mbi_unblock_punit_i2c_access();
 }
 
 int i2c_dw_probe_lock_support(struct dw_i2c_dev *dev)
@@ -166,14 +50,9 @@  int i2c_dw_probe_lock_support(struct dw_i2c_dev *dev)
 	dev->release_lock = baytrail_i2c_release;
 	dev->shared_with_punit = true;
 
-	pm_qos_add_request(&dev->pm_qos, PM_QOS_CPU_DMA_LATENCY,
-			   PM_QOS_DEFAULT_VALUE);
-
 	return 0;
 }
 
 void i2c_dw_remove_lock_support(struct dw_i2c_dev *dev)
 {
-	if (dev->acquire_lock)
-		pm_qos_remove_request(&dev->pm_qos);
 }