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Subject[PATCH v2 1/3] x86: baytrail/cherrytrail: Rework and move P-Unit PMIC bus semaphore code
Date
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(-)

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);
}
--
2.19.0
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