RE: [RFC PATCH 0/6] AXI FAN new features and improvements

Hi Guenter,

From: Nuno Sá <nuno.sa@analog.com>
Sent: Thursday, July 8, 2021 2:01 PM
To: linux-hwmon@vger.kernel.org; devicetree@vger.kernel.org
Cc: Guenter Roeck <linux@roeck-us.net>; Rob Herring
[off-list ref]; Jean Delvare [off-list ref]
Subject: [RFC PATCH 0/6] AXI FAN new features and improvements

This series adds some new features to the axi-fan-control driver. On
top
of that, the HW had some changes (basically it now starts automatically
out of reset) so that the driver needed some minor refactoring. The
reason I'm sending this as RFC, is mainly because of the last patch
("hwmon: axi-fan-control: support temperature vs pwm points"). The
core
has some predefined values which define a temperature vs pwm
curve [1].
It also exposes registers so that users can change it according to their
needs. As I could not find standard attributes in the subsystem, I'm
proposing some "raw" sysfs files. Looking at [2], the pwm_auto_point
stuff looked to be what I want. Obviously I might be wrong :). If this
is accepted, I will add a proper sysfs DOC file describing the new files
(being lazy in the RFC).

For patch 5 ("hwmon: axi-fan-control: clear the fan fault irq at
startup"),
it's also arguable if we really need it. The main reason I have it is
because of some userland apps that might take some drastic measures
by
just reading 1 fan_fault alarm. Obviously, we can argue that the
problem
is in the app and not in the driver. Though it's such a minimal change
that I decided to include it (I'm more than fine in dropping the patch).

[1]: https://wiki.analog.com/resources/fpga/docs/axi_fan_control
[2]:
https://urldefense.com/v3/__https://www.kernel.org/doc/Documen
tation/hwmon/sysfs-
interface__;!!A3Ni8CS0y2Y!uwjpaOT8QEBVfKTCWELJNbjJJ69iR7S3tKS
WV4B0K742CtcARkTtAqMxknnpPw$

Nuno Sá (6):
  hwmon: axi-fan-control: make sure the clock is enabled
  hwmon: axi-fan-control: add tacho devicetree properties
  dt-bindings: axi-fan-control: add tacho properties
  hwmon: axi-fan-control: handle irqs in natural order
  hwmon: axi-fan-control: clear the fan fault irq at startup
  hwmon: axi-fan-control: support temperature vs pwm points

The HW guy is willing to change how the core works. This means,
that all that unstable pwm - rpm points will go away and we will
have a register where we can set the minimum fan speed for
evaluating the FAN. He also said that the default value for the
this setting will be pretty low so that we should only have _real_ 
faults at startup which means patch 5 should not be needed
anymore...

Anyways, I will send a new pull with patches 1,3 and 5 and
as soon as I have some HW ready to test, I will send the other
patches. With the new mechanism, we can also simplify the IRQ
handling [1]...

For the new devicetree property, I think now it really is a fan
property which makes me wonder if the property will be accepted
in the controller bindings or if I need to send a fan.yaml...

[1]: https://elixir.bootlin.com/linux/v5.14-rc3/source/drivers/hwmon/axi-fan-control.c#L280

- Nuno Sá