hwmon: (pmbus/adm1266) add powerup_counter debugfs entry

The ADM1266 maintains a 16-bit non-volatile POWERUP_COUNTER register
(0xE4, datasheet Rev. D, Table 93) that increments on every power
cycle and cannot be reset by the host. Each blackbox record already
embeds the counter at record time, so the standalone live value is
primarily useful for matching a captured record back to the boot it
came from when correlating logs.

Expose it as a read-only debugfs file alongside sequencer_state. The
block-read returns two payload bytes in little-endian order.

Take pmbus_lock around the block-read so the access serialises with
any pmbus_core sequence that sets PAGE on the device. Without it, a
PAGE write from another thread could interleave between a PAGE set
and a paged read elsewhere in the driver and corrupt either side's
view of the device state machine.

Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
Assisted-by: Claude-Code:claude-opus-4-7
Assisted-by: sashiko:gemini-3.1-pro-preview
Link: https://lore.kernel.org/r/20260520-adm1266-v5-2-c72ef1fac1ea@nexthop.ai
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/pmbus/adm1266.c b/drivers/hwmon/pmbus/adm1266.c
index aa353b6b9c99353bde4843726bc3b1c5e42252cb..0ef8a6ccd919c2d5dc4466cc882c782e14e445bb 100644 (file)
--- a/drivers/hwmon/pmbus/adm1266.c
+++ b/drivers/hwmon/pmbus/adm1266.c
@@ -28,6 +28,7 @@
 #define ADM1266_READ_BLACKBOX  0xDE
 #define ADM1266_SET_RTC                0xDF
 #define ADM1266_GPIO_CONFIG    0xE1
+#define ADM1266_POWERUP_COUNTER        0xE4
 #define ADM1266_BLACKBOX_INFO  0xE6
 #define ADM1266_PDIO_STATUS    0xE9
 #define ADM1266_GPIO_STATUS    0xEA
@@ -371,6 +372,32 @@ static int adm1266_firmware_revision_read(struct seq_file *s, void *pdata)
        return 0;
 }
 
+/*
+ * POWERUP_COUNTER (0xE4) is a 2-byte little-endian non-volatile counter
+ * that increments on every device power cycle (datasheet Rev. D, Table
+ * 93). It saturates at 65535 and cannot be reset by the host. Each
+ * blackbox record embeds the counter value at record time, so this live
+ * read is mainly useful for matching a record back to its boot.
+ */
+static int adm1266_powerup_counter_read(struct seq_file *s, void *pdata)
+{
+       struct device *dev = s->private;
+       struct i2c_client *client = to_i2c_client(dev);
+       u8 buf[I2C_SMBUS_BLOCK_MAX];
+       int ret;
+
+       guard(pmbus_lock)(client);
+       ret = i2c_smbus_read_block_data(client, ADM1266_POWERUP_COUNTER, buf);
+       if (ret < 0)
+               return ret;
+       if (ret != 2)
+               return -EIO;
+
+       seq_printf(s, "%u\n", buf[0] | (buf[1] << 8));
+
+       return 0;
+}
+
 /*
  * Clearing the blackbox is required when the device is configured in
  * single-recording mode (BLACKBOX_CONFIG[0] = 0): once the 32-record
@@ -419,6 +446,8 @@ static void adm1266_init_debugfs(struct adm1266_data *data)
                                    adm1266_state_read);
        debugfs_create_devm_seqfile(&data->client->dev, "firmware_revision", data->debugfs_dir,
                                    adm1266_firmware_revision_read);
+       debugfs_create_devm_seqfile(&data->client->dev, "powerup_counter", data->debugfs_dir,
+                                   adm1266_powerup_counter_read);
        debugfs_create_file("clear_blackbox", 0200, data->debugfs_dir, data->client,
                            &adm1266_clear_blackbox_fops);
 }