[PATCH v4 0/3] hwmon: (pmbus/adm1266) add clear_blackbox and powerup_counter debugfs entries

[Abdurrahman Hussain]

This is what remains of the v3 series after Guenter applied patches
1/5 (firmware_revision) and 5/5 (GPIO line label) to hwmon-next, and
asked for patch 4/5 (rtc_class) to be dropped.

Patch 1 adds a write-only clear_blackbox debugfs file. Devices
configured for single-recording mode (BLACKBOX_CONFIG[0] = 0) need
an explicit clear once the 32-record buffer fills; the documented
sub-command ({0xFE, 0x00} block-write to 0xDE) wasn't reachable
from userspace. The patch also acquires pmbus_lock at the
adm1266_nvmem_read() callback boundary so the memset of
data->dev_mem, the blackbox refill, and the memcpy to userspace run
as a single critical section -- the nvmem core does not serialize
concurrent reg_read calls.

Patch 2 exposes the non-volatile POWERUP_COUNTER (0xE4) via debugfs.
The same value is embedded in every blackbox record, so the live
value lets userspace match a captured record back to the boot it
came from when correlating logs. The block-read is taken under
pmbus_lock to serialise against any pmbus_core PAGE+register
sequence on the device.

Patch 3 takes pmbus_lock in adm1266_state_read() (the pre-existing
sequencer_state debugfs handler) for the same defensive-locking
reason that motivates the new debugfs files in patches 1 and 2:
any direct device access from outside pmbus_core should be ordered
with respect to pmbus_core's own PAGE+register sequences.

Signed-off-by: Abdurrahman Hussain <abdurrahman@xxxxxxxxxx>
---
Changes in v4:
- Drop former patches 1 (firmware_revision) and 5 (GPIO line label):
  applied to hwmon-next by Guenter.
- Drop former patch 4 (rtc_class) per Guenter's review: turning the
  chip into a pseudo rtc_class device and making the driver depend
  on the RTC subsystem was rejected. The underlying CLOCK_MONOTONIC
  -vs- wall-clock bug in the original probe-time seed is fixed
  independently in the "hwmon: (pmbus/adm1266) buffer-bound and
  timestamp fixes" series sent in parallel, so the seed-at-probe
  behaviour becomes correct without this driver needing to depend
  on RTC_CLASS.
- Patch 1 (clear_blackbox, was 2/5): take pmbus_lock at the outer
  adm1266_nvmem_read() callback rather than inside
  adm1266_nvmem_read_blackbox() so it covers the memset of
  data->dev_mem, the refill, and the memcpy to userspace as a
  single critical section. The nvmem core does not serialize
  concurrent reg_read invocations, so the v3 placement still let
  the memset race with another reader's memcpy to userspace
  (Sashiko review of v3).
- Patch 2 (powerup_counter, was 3/5): take pmbus_lock around the
  block-read so the access serialises with any pmbus_core sequence
  that sets PAGE on the device (Sashiko review of v3).
- New patch 3: take pmbus_lock in adm1266_state_read() (the
  sequencer_state debugfs handler).  Same defensive-locking
  argument as patches 1 and 2; surfaced while folding similar
  fixes into the parallel "hwmon: (pmbus/adm1266) GPIO accessor
  fixes" series.
- Link to v3: https://patch.msgid.link/20260512-adm1266-v3-0-a81a479b0bb0@xxxxxxxxxx

Changes in v3:
- Patch 2: take guard(pmbus_lock)(client) in
  adm1266_clear_blackbox_write() and adm1266_nvmem_read_blackbox()
  to serialise the clear against the multi-record nvmem read loop
  (both share command 0xDE). Also move adm1266_config_nvmem() to
  after pmbus_do_probe() so the blackbox nvmem entry isn't exposed
  to userspace before the PMBus mutex is initialised (Sashiko
  review).
- Patch 4: take guard(pmbus_lock)(client) in the RTC
  read_time/set_time callbacks to serialise against the PMBus
  core's PAGE+register sequences. Move adm1266_register_rtc() to
  after pmbus_do_probe() for the same reason as the config_nvmem
  move; /dev/rtcN being opened by userspace (systemd-timesyncd,
  udev) before probe completed would otherwise hit an
  uninitialised mutex (observed on hardware, also flagged by
  Sashiko).
- Link to v2: https://patch.msgid.link/20260510-adm1266-v2-0-3a22b903c2f1@xxxxxxxxxx

Changes in v2:
- Drop the v1 "use wall-clock seconds for SET_RTC" and "write
  fractional-seconds field of SET_RTC" patches. v1 patch 6 already
  added an rtc_class device, so userspace now owns the time-set
  policy and the probe-time seed is no longer needed - removing it
  also fixes the cross-reboot blackbox-correlation regression the
  seed introduced.
- In the rtc_class patch, write the SET_RTC fractional-seconds
  bytes as zero rather than computing them from a timespec64. The
  rtc_class API is second-precision, so the divide that v1 patch 2
  was adding never produced a non-zero result anyway. This also
  drops the 64-bit divide that would have failed to link on 32-bit
  builds (Sashiko review).
- Use %d (decimal) for the I2C adapter number in GPIO line labels,
  matching the i2c-N convention used elsewhere in Linux. v1 used
  %x, which rendered bus numbers >= 10 in hexadecimal (Sashiko
  review).
- Link to v1: https://patch.msgid.link/20260508-adm1266-v1-0-ec08bf29e0ce@xxxxxxxxxx

To: Guenter Roeck <linux@xxxxxxxxxxxx>
To: Alexandru Tachici <alexandru.tachici@xxxxxxxxxx>
Cc: linux-hwmon@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx

---
Abdurrahman Hussain (3):
      hwmon: (pmbus/adm1266) add clear_blackbox debugfs entry
      hwmon: (pmbus/adm1266) add powerup_counter debugfs entry
      hwmon: (pmbus/adm1266) serialize sequencer_state debugfs read with pmbus_lock

 drivers/hwmon/pmbus/adm1266.c | 77 +++++++++++++++++++++++++++++++++++++++----
 1 file changed, 71 insertions(+), 6 deletions(-)
---
base-commit: 70eda68668d1476b459b64e69b8f36659fa9dfa8
change-id: 20260507-adm1266-cf3af42dc3d2

Best regards,
--  
Abdurrahman Hussain <abdurrahman@xxxxxxxxxx>