misc: Add power-efuse driver [LWN.net]

From:		Zev Weiss <zev-AT-bewilderbeest.net>
To:		linux-kernel-AT-vger.kernel.org, Greg Kroah-Hartman <gregkh-AT-linuxfoundation.org>, Arnd Bergmann <arnd-AT-arndb.de>
Subject:		[PATCH 0/4] misc: Add power-efuse driver
Date:		Thu, 17 Feb 2022 02:44:40 -0800
Message-ID:		<20220217104444.7695-1-zev@bewilderbeest.net>
Cc:		Zev Weiss <zev-AT-bewilderbeest.net>, openbmc-AT-lists.ozlabs.org, Rob Herring <robh+dt-AT-kernel.org>, Guenter Roeck <linux-AT-roeck-us.net>, Jean Delvare <jdelvare-AT-suse.com>, devicetree-AT-vger.kernel.org, linux-hwmon-AT-vger.kernel.org, Mark Brown <broonie-AT-kernel.org>, Liam Girdwood <lgirdwood-AT-gmail.com>
Archive-link:		Article

Hello,

This patch series is another incarnation of some previous efforts [0]
at enabling userspace access to the OPERATION state (and now status
flags) of PMBus devices, specifically with respect to efuses
protecting general-purpose power outputs.  This functionality is an
important component enabling a port of OpenBMC to the Delta AHE-50DC
Open19 power shelf [1].

The first patch extends the pmbus core's regulator support with an
implementation of the .get_error_flags() operation, mapping PMBus
status flags to REGULATOR_ERROR_* flags where possible, and the second
patch adds regulator support for the lm25066 driver.  These two
patches are essentially independent of the power-efuse driver (and
each other) and could potentially be applicable individually, but are
necessary for the power-efuse driver to be useful on the AHE-50DC.

The third and fourth patches add dt-bindings and the implementation of
the power-efuse driver, respectively.  The driver is fairly simple; it
merely provides a sysfs interface to enable, disable, and retrieve
error flags from an underlying regulator.

There is one aspect of its usage of the regulator API I'm a bit
uncertain about, however: this driver seems like a case where an
exclusive 'get' of the regulator (i.e. devm_regulator_get_exclusive()
instead of devm_regulator_get() in efuse_probe()) would be
appropriate, since in the intended usage no other device should be
using an efuse's regulator.  With an exclusive get though, the
regulator's use_count and the consumer's enable_count don't balance
out properly to allow the enable/disable operations to work properly
(the former ending up one more than the latter, leading to
enable_count underflows on attempts to disable the regulator).  So at
least for now it's using a non-exclusive get -- I'd be happy to hear
any pointers on a way to allow an exclusive get to work here, though.


Thanks,
Zev

[0] https://lore.kernel.org/openbmc/YGLepYLvtlO6Ikzs@hatter.b...
[1] https://www.open19.org/marketplace/delta-16kw-power-shelf/

Zev Weiss (4):
  hwmon: (pmbus) Add get_error_flags support to regulator ops
  hwmon: (pmbus) lm25066: Add regulator support
  dt-bindings: Add power-efuse binding
  misc: Add power-efuse driver

 .../devicetree/bindings/misc/power-efuse.yaml |  37 +++
 MAINTAINERS                                   |   5 +
 drivers/hwmon/pmbus/Kconfig                   |   7 +
 drivers/hwmon/pmbus/lm25066.c                 |  14 ++
 drivers/hwmon/pmbus/pmbus_core.c              |  97 ++++++++
 drivers/misc/Kconfig                          |  15 ++
 drivers/misc/Makefile                         |   1 +
 drivers/misc/power-efuse.c                    | 221 ++++++++++++++++++
 8 files changed, 397 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/misc/power-efuse.yaml
 create mode 100644 drivers/misc/power-efuse.c

-- 
2.35.1