Re: [RFC 1/8] dt-bindings: mfd: Add Altera Arria10 System Resource Chip bindings

Guenter Roeck
2016-04-20T01:48:54Z

On 04/19/2016 07:38 AM, Thor Thayer wrote:

On 04/19/2016 02:23 AM, Lee Jones wrote:

On Mon, 18 Apr 2016, Thor Thayer wrote:

Hi Lee,

On 04/18/2016 02:45 AM, Lee Jones wrote:

On Fri, 15 Apr 2016, Thor Thayer wrote:

On 03/30/2016 06:35 AM, Lee Jones wrote:

On Tue, 29 Mar 2016, ttha...@opensource.altera.com wrote:

From: Thor Thayer <ttha...@opensource.altera.com>
To: linux-hwmon@vger.kernel.org

The Altera Arria10 Devkit System Resource chip is a Multi-Function
Device, it has two subdevices:
- GPIO
- HWMON

This patch adds documentation for the Altera A10-SR DT bindings.

Signed-off-by: Thor Thayer <ttha...@opensource.altera.com>
---
.../devicetree/bindings/mfd/altera-a10sr.txt | 35 ++++++++++++++++++++
1 file changed, 35 insertions(+)
create mode 100644 Documentation/devicetree/bindings/mfd/altera-a10sr.txt

diff --git a/Documentation/devicetree/bindings/mfd/altera-a10sr.txt
b/Documentation/devicetree/bindings/mfd/altera-a10sr.txt
new file mode 100644
index 0000000..564c761
--- /dev/null
+++ b/Documentation/devicetree/bindings/mfd/altera-a10sr.txt
@@ -0,0 +1,35 @@
+* Altera Arria10 Development Kit System Resource Chip
+
+Required parent device properties:
+- compatible : "altr,altr_a10sr"
+- spi-max-frequency : Maximum SPI frequency.
+- reg : the SPI Chip Select address for the Arria10 System Resource chip

[...]

+ a10sr_hwmon: a10sr_hwmon {

Device type only please.

I need to revisit where this will live (hwmon does not seem to be
the correct place) so it will change but I can follow the format
above if it is correct.

BTW, "hwmon" is a subsystem in Linux, therefore is a Linuxism and is
not allowed in DT. What does the device *actually* do?

OK. I'll be careful not to introduce the Linux subsystem name.

This module indicates whether the power supplies are at the correct
voltage. It uses a boolean instead of giving an actual voltage value
as required by HWMON. In other words it is a comparator instead of
an Analog-to-Digital Converter.

I could call it a power supply supervisor or voltage status monitor
but it only acts in a passive role. There is no output to trigger an
error - only polling, so supervisor doesn't seem like a good name.

Maybe something like this?

power_supply_status {
compatible = "altr,a10sr-hwmon";
}

Thanks for reviewing and helping me figure out the device tree naming.

Does it have its own address space? How complex is the device? Not
very, by the sounds of it. In which case, does it really need its own
driver?

Yes, you are correct that the voltage status is not very complex but I'd need a
driver to expose these signals.

A completely different option might be to expose the signals as gpio pins.

Guenter

I initially started with an MFD because it was similar to the other MFD
drivers. The device has GPI, GPO, voltage status, device enables, device
present indications, and device resets.

There is a discussion now on where the voltage status driver should live (iio/
, hwmon/, misc/). It isn't clear to me where the device enables, device present
indications and voltage status would go. I'm leaning toward a driver in the
misc/ directory that would cover all of these. In that case, this wouldn't be a
MFD driver.

Any thoughts or suggestions?

Thanks,

Thor

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