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

[Rafael J. Wysocki]

On Sun, Sep 23, 2018 at 4:45 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>

If there are no objections or concerns regarding this patch, I'm
inclined to take the entire series including it.

> ---
> 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.
> ---
>  arch/x86/include/asm/iosf_mbi.h              |  39 +++--
>  arch/x86/platform/intel/iosf_mbi.c           | 161 +++++++++++++++++--
>  drivers/i2c/busses/i2c-designware-baytrail.c | 125 +-------------
>  3 files changed, 180 insertions(+), 145 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..5623a315f004 100644
> --- a/arch/x86/platform/intel/iosf_mbi.c
> +++ b/arch/x86/platform/intel/iosf_mbi.c
> @@ -18,12 +18,14 @@
>   * 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>
>
> @@ -34,8 +36,8 @@
>
>  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 +230,113 @@ 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);
> +       mutex_unlock(&iosf_mbi_punit_mutex);
> +}
> +
> +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));
> +                       goto out; /* Success, done. */
> +               }
> +
> +               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();
> +
> +       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();
> +               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 +374,14 @@ 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 +466,7 @@ 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;
>
> @@ -349,12 +477,16 @@ 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_BAYTRAIL),
> +         .driver_data = PUNIT_SEMAPHORE_BYT },
> +       { PCI_DEVICE(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_BRASWELL),
> +         .driver_data = PUNIT_SEMAPHORE_CHT },
>         { PCI_DEVICE(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_QUARK_X1000) },
>         { PCI_DEVICE(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_TANGIER) },
>         { 0, },
> @@ -371,6 +503,9 @@ 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 +516,8 @@ 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.rc1
>