linux-kernel - [PATCH v2 0/2] misc: Add power-efuse driver

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Message-Id: <20220308011811.10353-1-zev@bewilderbeest.net>
Date:   Mon,  7 Mar 2022 17:18:08 -0800
From:   Zev Weiss <zev@...ilderbeest.net>
To:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Zev Weiss <zev@...ilderbeest.net>, openbmc@...ts.ozlabs.org,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>
Subject: [PATCH v2 0/2] misc: Add power-efuse driver

Hello,

This is a second revision of the v1 patch series posted previously
[2].

Changes since v1:
 - dropped pmbus/lm25066 patches, submitted separately via hwmon tree [Guenter]
 - fixed indentation in power-efuse.yaml [Rob's bot]
 - added more detailed description in power-efuse.yaml [Rob]
 - added sysfs ABI documentation [Greg]
 - replaced manual struct attribute_group and sysfs_create_group()
   with ATTRIBUTE_GROUPS() and driver.dev_groups [Greg]

A lightly edited version of the previous cover letter follows.

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 adds dt-bindings, and the second adds the
implementation of the power-efuse driver.  The driver is fairly
simple; it merely provides a sysfs interface to enable, disable, and
retrieve error flags from an underlying regulator (which in the
expected usage will most likely be a PMBus device).

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.bewilderbeest.net/
[1] https://www.open19.org/marketplace/delta-16kw-power-shelf/
[2] https://lore.kernel.org/openbmc/20220217104444.7695-1-zev@bewilderbeest.net/

Zev Weiss (2):
  dt-bindings: Add power-efuse binding
  misc: Add power-efuse driver

 .../ABI/testing/sysfs-driver-power-efuse      |  32 +++
 .../devicetree/bindings/misc/power-efuse.yaml |  49 ++++
 MAINTAINERS                                   |   5 +
 drivers/misc/Kconfig                          |  15 ++
 drivers/misc/Makefile                         |   1 +
 drivers/misc/power-efuse.c                    | 212 ++++++++++++++++++
 6 files changed, 314 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-driver-power-efuse
 create mode 100644 Documentation/devicetree/bindings/misc/power-efuse.yaml
 create mode 100644 drivers/misc/power-efuse.c

-- 
2.35.1