linux-kernel - Re: [PATCH 0/4] misc: Add power-efuse driver

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Date:   Thu, 17 Feb 2022 10:14:18 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Zev Weiss <zev@...ilderbeest.net>, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     openbmc@...ts.ozlabs.org, Rob Herring <robh+dt@...nel.org>,
        Jean Delvare <jdelvare@...e.com>, devicetree@...r.kernel.org,
        linux-hwmon@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>
Subject: Re: [PATCH 0/4] misc: Add power-efuse driver

On 2/17/22 02:44, Zev Weiss wrote:
> 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.
> 

Nevertheless, the first two patches are orthogonal to the remaining
two patches and should be separate.

Guenter

> 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.bewilderbeest.net/
> [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
>