[0/4] misc: Add power-efuse driver

Message

Zev Weiss Feb. 17, 2022, 10:44 a.m. UTC

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/[e-mail]/
[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

Comments

Guenter Roeck Feb. 17, 2022, 6:14 p.m. UTC | #1

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/[e-mail]/
> [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
>