On Mon, May 18, 2020 at 10:50 PM Lars Povlsen
[off-list ref] wrote:

Linus Walleij writes:

quoted

On Wed, May 13, 2020 at 4:11 PM Lars Povlsen [off-list ref] wrote:

quoted

This adds DT bindings for the Microsemi SGPIO controller, bindings
mscc,ocelot-sgpio and mscc,luton-sgpio.

Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Lars Povlsen <redacted>

quoted

+  microchip,sgpio-ports:
+    description: This is a 32-bit bitmask, configuring whether a
+      particular port in the controller is enabled or not. This allows
+      unused ports to be removed from the bitstream and reduce latency.
+    $ref: "/schemas/types.yaml#/definitions/uint32"

I don't know about this.

You are saying this pin controller can have up to 32 GPIO "ports"
(also known as banks).

Why can't you just represent each such port as a separate GPIO
node:

pinctrl@nnn {
    gpio@0 {
        ....
    };
    gpio@1 {
        ....
    };
    ....
    gpio@31 {
        ....
    };
};

Then if some of them are unused just set it to status = "disabled";

This also makes your Linux driver simpler because each GPIO port
just becomes a set of 32bit registers and you can use
select GPIO_GENERIC and bgpio_init() and save a whole
slew of standard stock code.

Linus, thank you for your input.

The controller handles an array of 32*n signals, where n >= 1 && n <=
4.

The problem with the above approach is that the ports are disabled
*port*-wise - so they remove all (upto) 4 bits. That would be across the
banks.

You could of course have the "implied" semantics that a disabled port at
any bit position disabled all (bit positions for the same port).

I don't understand this, you would have to elaborate...

In any case microchip,sgpio-ports is probably not the right thing,
use ngpios which is documented and just divide by 32 to get the
number of ports I think? But that is just in case they get
enabled strictly in sequence, otherwise you'd need a custom
property.

Yours,
Linus Walleij