Re: [PATCH v2] hwmon (occ): Delay hwmon registration until user request

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On 4/29/22 02:13, Joel Stanley wrote:

On Wed, 27 Apr 2022 at 14:34, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:

On Wed, Apr 27, 2022 at 09:04:43AM -0500, Eddie James wrote:

Instead of registering the hwmon device at probe time, use the
existing "occ_active" sysfs file to control when the driver polls
the OCC for sensor data and registers with hwmon. The reason for
this change is that the SBE, which is the device by which the
driver communicates with the OCC, cannot handle communications
during certain system state transitions, resulting in
unrecoverable system errors.

Signed-off-by: Eddie James <eajames@xxxxxxxxxxxxx>

Applied to hwmon-next.

Will this change break existing userspace? As I understand it existing
systems rely on the driver probing for the occ without extra
interaction.
Yes, the one application that uses this driver will not work correctly if it's not updated to the latest version. For BMCs, typically kernels and userspace are built and installed together, so I don't anticipate any problems for end users. 




 From your commit message, it sounds like we should inhibit SBE
communication during the sensitive period. This would stop any
devices, not just the OCC, from generating unwanted traffic.
That is true, and could be a good option, however it would require a brand new interface to the SBE FIFO driver. This change re-uses the occ_active file to effect the desired behavior. 


Thanks,

Eddie





Guenter


---
Changes since v1:
  - Update commit message to for clarity.

  drivers/hwmon/occ/common.c | 100 +++++++++++++++++++--------
  drivers/hwmon/occ/common.h |   5 +-
  drivers/hwmon/occ/p8_i2c.c |   2 +-
  drivers/hwmon/occ/p9_sbe.c |   2 +-
  drivers/hwmon/occ/sysfs.c  | 137 ++++++++++++++++++++++---------------
  5 files changed, 156 insertions(+), 90 deletions(-)

diff --git a/drivers/hwmon/occ/common.c b/drivers/hwmon/occ/common.c
index f00cd59f1d19..d78f4bebc718 100644
--- a/drivers/hwmon/occ/common.c
+++ b/drivers/hwmon/occ/common.c
@@ -1149,44 +1149,75 @@ static void occ_parse_poll_response(struct occ *occ)
               sizeof(*header), size + sizeof(*header));
  }

-int occ_setup(struct occ *occ, const char *name)
+int occ_active(struct occ *occ, bool active)
  {
-     int rc;
-
-     mutex_init(&occ->lock);
-     occ->groups[0] = &occ->group;
+     int rc = mutex_lock_interruptible(&occ->lock);

-     /* no need to lock */
-     rc = occ_poll(occ);
-     if (rc == -ESHUTDOWN) {
-             dev_info(occ->bus_dev, "host is not ready\n");
-             return rc;
-     } else if (rc < 0) {
-             dev_err(occ->bus_dev,
-                     "failed to get OCC poll response=%02x: %d\n",
-                     occ->resp.return_status, rc);
+     if (rc)
               return rc;
-     }

-     occ->next_update = jiffies + OCC_UPDATE_FREQUENCY;
-     occ_parse_poll_response(occ);
+     if (active) {
+             if (occ->active) {
+                     rc = -EALREADY;
+                     goto unlock;
+             }

-     rc = occ_setup_sensor_attrs(occ);
-     if (rc) {
-             dev_err(occ->bus_dev, "failed to setup sensor attrs: %d\n",
-                     rc);
-             return rc;
-     }
+             occ->error_count = 0;
+             occ->last_safe = 0;

-     occ->hwmon = devm_hwmon_device_register_with_groups(occ->bus_dev, name,
-                                                         occ, occ->groups);
-     if (IS_ERR(occ->hwmon)) {
-             rc = PTR_ERR(occ->hwmon);
-             dev_err(occ->bus_dev, "failed to register hwmon device: %d\n",
-                     rc);
-             return rc;
+             rc = occ_poll(occ);
+             if (rc < 0) {
+                     dev_err(occ->bus_dev,
+                             "failed to get OCC poll response=%02x: %d\n",
+                             occ->resp.return_status, rc);
+                     goto unlock;
+             }
+
+             occ->active = true;
+             occ->next_update = jiffies + OCC_UPDATE_FREQUENCY;
+             occ_parse_poll_response(occ);
+
+             rc = occ_setup_sensor_attrs(occ);
+             if (rc) {
+                     dev_err(occ->bus_dev,
+                             "failed to setup sensor attrs: %d\n", rc);
+                     goto unlock;
+             }
+
+             occ->hwmon = hwmon_device_register_with_groups(occ->bus_dev,
+                                                            "occ", occ,
+                                                            occ->groups);
+             if (IS_ERR(occ->hwmon)) {
+                     rc = PTR_ERR(occ->hwmon);
+                     occ->hwmon = NULL;
+                     dev_err(occ->bus_dev,
+                             "failed to register hwmon device: %d\n", rc);
+                     goto unlock;
+             }
+     } else {
+             if (!occ->active) {
+                     rc = -EALREADY;
+                     goto unlock;
+             }
+
+             if (occ->hwmon)
+                     hwmon_device_unregister(occ->hwmon);
+             occ->active = false;
+             occ->hwmon = NULL;
       }

+unlock:
+     mutex_unlock(&occ->lock);
+     return rc;
+}
+
+int occ_setup(struct occ *occ)
+{
+     int rc;
+
+     mutex_init(&occ->lock);
+     occ->groups[0] = &occ->group;
+
       rc = occ_setup_sysfs(occ);
       if (rc)
               dev_err(occ->bus_dev, "failed to setup sysfs: %d\n", rc);
@@ -1195,6 +1226,15 @@ int occ_setup(struct occ *occ, const char *name)
  }
  EXPORT_SYMBOL_GPL(occ_setup);

+void occ_shutdown(struct occ *occ)
+{
+     occ_shutdown_sysfs(occ);
+
+     if (occ->hwmon)
+             hwmon_device_unregister(occ->hwmon);
+}
+EXPORT_SYMBOL_GPL(occ_shutdown);
+
  MODULE_AUTHOR("Eddie James <eajames@xxxxxxxxxxxxx>");
  MODULE_DESCRIPTION("Common OCC hwmon code");
  MODULE_LICENSE("GPL");
diff --git a/drivers/hwmon/occ/common.h b/drivers/hwmon/occ/common.h
index 2dd4a4d240c0..64d5ec7e169b 100644
--- a/drivers/hwmon/occ/common.h
+++ b/drivers/hwmon/occ/common.h
@@ -106,6 +106,7 @@ struct occ {
       struct attribute_group group;
       const struct attribute_group *groups[2];

+     bool active;
       int error;                      /* final transfer error after retry */
       int last_error;                 /* latest transfer error */
       unsigned int error_count;       /* number of xfr errors observed */
@@ -123,9 +124,11 @@ struct occ {
       u8 prev_mode;
  };

-int occ_setup(struct occ *occ, const char *name);
+int occ_active(struct occ *occ, bool active);
+int occ_setup(struct occ *occ);
  int occ_setup_sysfs(struct occ *occ);
  void occ_shutdown(struct occ *occ);
+void occ_shutdown_sysfs(struct occ *occ);
  void occ_sysfs_poll_done(struct occ *occ);
  int occ_update_response(struct occ *occ);

diff --git a/drivers/hwmon/occ/p8_i2c.c b/drivers/hwmon/occ/p8_i2c.c
index 9e61e1fb5142..da39ea28df31 100644
--- a/drivers/hwmon/occ/p8_i2c.c
+++ b/drivers/hwmon/occ/p8_i2c.c
@@ -223,7 +223,7 @@ static int p8_i2c_occ_probe(struct i2c_client *client)
       occ->poll_cmd_data = 0x10;              /* P8 OCC poll data */
       occ->send_cmd = p8_i2c_occ_send_cmd;

-     return occ_setup(occ, "p8_occ");
+     return occ_setup(occ);
  }

  static int p8_i2c_occ_remove(struct i2c_client *client)
diff --git a/drivers/hwmon/occ/p9_sbe.c b/drivers/hwmon/occ/p9_sbe.c
index 49b13cc01073..42fc7b97bb34 100644
--- a/drivers/hwmon/occ/p9_sbe.c
+++ b/drivers/hwmon/occ/p9_sbe.c
@@ -145,7 +145,7 @@ static int p9_sbe_occ_probe(struct platform_device *pdev)
       occ->poll_cmd_data = 0x20;              /* P9 OCC poll data */
       occ->send_cmd = p9_sbe_occ_send_cmd;

-     rc = occ_setup(occ, "p9_occ");
+     rc = occ_setup(occ);
       if (rc == -ESHUTDOWN)
               rc = -ENODEV;   /* Host is shutdown, don't spew errors */

diff --git a/drivers/hwmon/occ/sysfs.c b/drivers/hwmon/occ/sysfs.c
index b2f788a77746..2317301fc1e9 100644
--- a/drivers/hwmon/occ/sysfs.c
+++ b/drivers/hwmon/occ/sysfs.c
@@ -6,13 +6,13 @@
  #include <linux/export.h>
  #include <linux/hwmon-sysfs.h>
  #include <linux/kernel.h>
+#include <linux/kstrtox.h>
  #include <linux/sysfs.h>

  #include "common.h"

  /* OCC status register */
  #define OCC_STAT_MASTER                      BIT(7)
-#define OCC_STAT_ACTIVE                      BIT(0)

  /* OCC extended status register */
  #define OCC_EXT_STAT_DVFS_OT         BIT(7)
@@ -22,6 +22,25 @@
  #define OCC_EXT_STAT_DVFS_VDD                BIT(3)
  #define OCC_EXT_STAT_GPU_THROTTLE    GENMASK(2, 0)

+static ssize_t occ_active_store(struct device *dev,
+                             struct device_attribute *attr,
+                             const char *buf, size_t count)
+{
+     int rc;
+     bool active;
+     struct occ *occ = dev_get_drvdata(dev);
+
+     rc = kstrtobool(buf, &active);
+     if (rc)
+             return rc;
+
+     rc = occ_active(occ, active);
+     if (rc)
+             return rc;
+
+     return count;
+}
+
  static ssize_t occ_sysfs_show(struct device *dev,
                             struct device_attribute *attr, char *buf)
  {
@@ -31,54 +50,64 @@ static ssize_t occ_sysfs_show(struct device *dev,
       struct occ_poll_response_header *header;
       struct sensor_device_attribute *sattr = to_sensor_dev_attr(attr);

-     rc = occ_update_response(occ);
-     if (rc)
-             return rc;
+     if (occ->active) {
+             rc = occ_update_response(occ);
+             if (rc)
+                     return rc;

-     header = (struct occ_poll_response_header *)occ->resp.data;
-
-     switch (sattr->index) {
-     case 0:
-             val = !!(header->status & OCC_STAT_MASTER);
-             break;
-     case 1:
-             val = !!(header->status & OCC_STAT_ACTIVE);
-             break;
-     case 2:
-             val = !!(header->ext_status & OCC_EXT_STAT_DVFS_OT);
-             break;
-     case 3:
-             val = !!(header->ext_status & OCC_EXT_STAT_DVFS_POWER);
-             break;
-     case 4:
-             val = !!(header->ext_status & OCC_EXT_STAT_MEM_THROTTLE);
-             break;
-     case 5:
-             val = !!(header->ext_status & OCC_EXT_STAT_QUICK_DROP);
-             break;
-     case 6:
-             val = header->occ_state;
-             break;
-     case 7:
-             if (header->status & OCC_STAT_MASTER)
-                     val = hweight8(header->occs_present);
-             else
+             header = (struct occ_poll_response_header *)occ->resp.data;
+
+             switch (sattr->index) {
+             case 0:
+                     val = !!(header->status & OCC_STAT_MASTER);
+                     break;
+             case 1:
                       val = 1;
-             break;
-     case 8:
-             val = header->ips_status;
-             break;
-     case 9:
-             val = header->mode;
-             break;
-     case 10:
-             val = !!(header->ext_status & OCC_EXT_STAT_DVFS_VDD);
-             break;
-     case 11:
-             val = header->ext_status & OCC_EXT_STAT_GPU_THROTTLE;
-             break;
-     default:
-             return -EINVAL;
+                     break;
+             case 2:
+                     val = !!(header->ext_status & OCC_EXT_STAT_DVFS_OT);
+                     break;
+             case 3:
+                     val = !!(header->ext_status & OCC_EXT_STAT_DVFS_POWER);
+                     break;
+             case 4:
+                     val = !!(header->ext_status &
+                              OCC_EXT_STAT_MEM_THROTTLE);
+                     break;
+             case 5:
+                     val = !!(header->ext_status & OCC_EXT_STAT_QUICK_DROP);
+                     break;
+             case 6:
+                     val = header->occ_state;
+                     break;
+             case 7:
+                     if (header->status & OCC_STAT_MASTER)
+                             val = hweight8(header->occs_present);
+                     else
+                             val = 1;
+                     break;
+             case 8:
+                     val = header->ips_status;
+                     break;
+             case 9:
+                     val = header->mode;
+                     break;
+             case 10:
+                     val = !!(header->ext_status & OCC_EXT_STAT_DVFS_VDD);
+                     break;
+             case 11:
+                     val = header->ext_status & OCC_EXT_STAT_GPU_THROTTLE;
+                     break;
+             default:
+                     return -EINVAL;
+             }
+     } else {
+             if (sattr->index == 1)
+                     val = 0;
+             else if (sattr->index <= 11)
+                     val = -ENODATA;
+             else
+                     return -EINVAL;
       }

       return sysfs_emit(buf, "%d\n", val);
@@ -95,7 +124,8 @@ static ssize_t occ_error_show(struct device *dev,
  }

  static SENSOR_DEVICE_ATTR(occ_master, 0444, occ_sysfs_show, NULL, 0);
-static SENSOR_DEVICE_ATTR(occ_active, 0444, occ_sysfs_show, NULL, 1);
+static SENSOR_DEVICE_ATTR(occ_active, 0644, occ_sysfs_show, occ_active_store,
+                       1);
  static SENSOR_DEVICE_ATTR(occ_dvfs_overtemp, 0444, occ_sysfs_show, NULL, 2);
  static SENSOR_DEVICE_ATTR(occ_dvfs_power, 0444, occ_sysfs_show, NULL, 3);
  static SENSOR_DEVICE_ATTR(occ_mem_throttle, 0444, occ_sysfs_show, NULL, 4);
@@ -139,7 +169,7 @@ void occ_sysfs_poll_done(struct occ *occ)
        * On the first poll response, we haven't yet created the sysfs
        * attributes, so don't make any notify calls.
        */
-     if (!occ->hwmon)
+     if (!occ->active)
               goto done;

       if ((header->status & OCC_STAT_MASTER) !=
@@ -148,12 +178,6 @@ void occ_sysfs_poll_done(struct occ *occ)
               sysfs_notify(&occ->bus_dev->kobj, NULL, name);
       }

-     if ((header->status & OCC_STAT_ACTIVE) !=
-         (occ->prev_stat & OCC_STAT_ACTIVE)) {
-             name = sensor_dev_attr_occ_active.dev_attr.attr.name;
-             sysfs_notify(&occ->bus_dev->kobj, NULL, name);
-     }
-
       if ((header->ext_status & OCC_EXT_STAT_DVFS_OT) !=
           (occ->prev_ext_stat & OCC_EXT_STAT_DVFS_OT)) {
               name = sensor_dev_attr_occ_dvfs_overtemp.dev_attr.attr.name;
@@ -227,8 +251,7 @@ int occ_setup_sysfs(struct occ *occ)
       return sysfs_create_group(&occ->bus_dev->kobj, &occ_sysfs);
  }

-void occ_shutdown(struct occ *occ)
+void occ_shutdown_sysfs(struct occ *occ)
  {
       sysfs_remove_group(&occ->bus_dev->kobj, &occ_sysfs);
  }
-EXPORT_SYMBOL_GPL(occ_shutdown);
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