Linus Walleij writes:

Hi Lars,

thanks for your patch!

You're welcome - thank you for you taking time to review it!

On Thu, Sep 3, 2020 at 3:35 PM Lars Povlsen [off-list ref] wrote:

quoted

This adds DT bindings for the Microsemi/Microchip SGPIO controller,

What I do not understand is why this GPIO controller is placed in the
bindings of the pin controllers? Do you plan to add pin control
properties to the bindings in the future?

I have made provisions for some of the generic pinconf parameters, and
since the controller also has support for some alternate modes like
(syncronized) blink at various rates, I thought I better add it as
pinctrl straight away.

quoted

+description: |
+  By using a serial interface, the SIO controller significantly extend
+  the number of available GPIOs with a minimum number of additional
+  pins on the device. The primary purpose of the SIO controllers is to
+  connect control signals from SFP modules and to act as an LED
+  controller.

This doesn't sound like it will ever be pin control?

above.

quoted

+  gpio-controller: true
+
+  '#gpio-cells':
+    description: GPIO consumers must specify four arguments, first the
+      port number, then the bit number, then a input/output flag and
+      finally the GPIO flags (from include/dt-bindings/gpio/gpio.h).
+      The dt-bindings/gpio/mchp-sgpio.h file define manifest constants
+      PIN_INPUT and PIN_OUTPUT.
+    const: 4

I do not follow this new third input/output flag at all.

Its actually a sort of bank address, since the individual "pins" are
unidirectional.

The PIN_INPUT/PIN_OUTPUT is defined in similar fashion in other pinctrl
binding header files... I can drop the define and use, but as it will be
used to address individual pins, I think it adds to readability.

Like this (excerpts from a DT with a switchdev driver using SFP's and
LED's on sgpio):

/{
	leds {
		compatible = "gpio-leds";
		led@0 {
			label = "eth60:yellow";
			gpios = <&sgpio1 28 0 PIN_OUTPUT GPIO_ACTIVE_LOW>;
			default-state = "off";
		};
		...
	};
};

&axi {
	sfp_eth60: sfp-eth60 {
		compatible	   = "sff,sfp";
		i2c-bus            = <&i2c152>;
		tx-disable-gpios   = <&sgpio2 28 0 PIN_OUTPUT GPIO_ACTIVE_LOW>;
		rate-select0-gpios = <&sgpio2 28 1 PIN_OUTPUT GPIO_ACTIVE_HIGH>;
		los-gpios          = <&sgpio2 28 0 PIN_INPUT GPIO_ACTIVE_HIGH>;
		mod-def0-gpios     = <&sgpio2 28 1 PIN_INPUT GPIO_ACTIVE_LOW>;
		tx-fault-gpios     = <&sgpio2 28 2 PIN_INPUT GPIO_ACTIVE_HIGH>;
	};
	...
};
                

- If it is a property of the hardware, it is something the driver should
  handle by determining which hardware it is from the compatible
  string.

- If it is a configuration it should be turned into something that is generic
  and useful for *all* GPIO controllers. If it is pin config it should use
  the pinconf bindings rather than shortcuts like this, but I think it is
  something the driver can do as an effect of the pin being requested
  as input or output in the operating system, depending on who the
  consumer is. Linux for example has GPIOD_OUT_LOW,
  GPIOD_OUT_HIGH, GPIOD_IN, GPIOD_ASIS...

- Is it not just a hog? We have bindings for those.

I hope the above shed some light on this.

quoted

+  microchip,sgpio-port-ranges:
+    description: This is a sequence of tuples, defining intervals of
+      enabled ports in the serial input stream. The enabled ports must
+      match the hardware configuration in order for signals to be
+      properly written/read to/from the controller holding
+      registers. Being tuples, then number of arguments must be
+      even. The tuples mast be ordered (low, high) and are
+      inclusive. Arguments must be between 0 and 31.
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+    minItems: 2
+    maxItems: 64

And you are *absolutely sure* that you can't just figure this out
from the compatible string? Or add a few compatible strings for
the existing variants?

Yes, this really needs to be configured for each board individually -
and cant be probed. It defines how the bitstream to/from the shift
registers is constructed/demuxed.

quoted

+  microchip,sgpio-frequency:
+    description: The sgpio controller frequency (Hz). This dictates
+      the serial bitstream speed, which again affects the latency in
+      getting control signals back and forth between external shift
+      registers. The speed must be no larger than half the system
+      clock, and larger than zero.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    minimum: 1
+    default: 12500000

I understand why you need this binding now, OK.

quoted

+/* mchp-sgpio specific pin type defines */
+#undef PIN_OUTPUT
+#undef PIN_INPUT
+#define PIN_OUTPUT     0
+#define PIN_INPUT      1

I'm not a fan of this. It seems like something that should be set in
response to the gpiochip callbacks .direction_input and
.direction_output callbacks.

As I tried to explain above, its a part of the pin address - aka bank
selector - whether your are accessing the input or the output side. And
since the directions have totally different - and concurrent - use, they
need to be individually addressed, not "configured".

In the example presented, sgpio2-p28b0 IN is loss-of-signal, and the
OUT is the sfp tx-disable control.

Yours,
Linus Walleij

---Lars

-- 
Lars Povlsen,
Microchip

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