The 05/28/2021 16:35, Linus Walleij wrote:

On Fri, May 28, 2021 at 6:10 AM Steven Lee [off-list ref] wrote:

quoted

The 05/28/2021 07:51, Linus Walleij wrote:

quoted

On Thu, May 27, 2021 at 2:55 AM Steven Lee [off-list ref] wrote:

quoted

+  max-ngpios:
+    description:
+      represents the number of actual hardware-supported GPIOs (ie,
+      slots within the clocked serial GPIO data). Since each HW GPIO is both an
+      input and an output, we provide max_ngpios * 2 lines on our gpiochip
+      device. We also use it to define the split between the inputs and
+      outputs; the inputs start at line 0, the outputs start at max_ngpios.
+    minimum: 0
+    maximum: 128

Why can this not be derived from the compatible value?

Normally there should be one compatible per hardware variant
of the block. And this should be aligned with that, should it not?

If this is not the case, maybe more detailed compatible strings
are needed, maybe double compatibles with compatible per
family and SoC?

Thanks for your suggestion.
I add max-ngpios in dt-bindings as there is ngpios defined in
dt-bindings, users can get the both max-ngpios and ngpios information
from dtsi without digging sgpio driver.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/aspeed-g5.dtsi#n354

If adding more detailed compatibles is better, I will add them to sgpio driver
in V3 patch and remove max-ngpios from dt-bindings.

Since AST2600 has 2 sgpio controller one with 128 pins and another one with 80 pins.
For supporting max-ngpios in compatibles, 2 platform data for each
ast2600 sgpio controller as follows are necessary.

static const struct aspeed_sgpio_pdata ast2600_sgpiom1_pdata = {
        .max_ngpios = 128;
};
static const struct aspeed_sgpio_pdata ast2600_sgpiom2_pdata = {
        .max_ngpios = 80;
};

{ .compatible = "aspeed,ast2500-sgpio" , .data = &ast2400_sgpio_pdata, },
{ .compatible = "aspeed,ast2600-sgpiom1", .data = &ast2600_sgpiom1_pdata, },
{ .compatible = "aspeed,ast2600-sgpiom2", .data = &ast2600_sgpiom2_pdata, },

There is a soft border between two IP blocks being "compatible"
and parameterized and two IP blocks being different and having
unique compatibles.

For example we know for sure we don't use different compatibles
because of how interrupt lines or DMA channels are connected.

Thanks for sharing the knowledge and examples.

So if this is an external thing, outside of the IP itself, I might back
off on this and say it shall be a parameter.

But max-ngpios? It is confusingly similar to ngpios.

So we need to think about this name.

Something like gpio-hardware-slots or something else that
really describe what this is.

Does this always strictly follow ngpios so that the number
of gpio slots == ngpios * 2? In that case only put ngpios into
the device tree and multiply by 2 in the driver, because ngpios
is exactly for this: parameterizing hardware limitations.

The parameter max-ngpios is the maxmum number of gpio pins that SoC supported,
ngpios is the maximum number of gpio pins that sgpio devices(e.g. sgpio cards) supported.

For instance, a sgpio card that supports 64 gpio pins which is connected to
ast2600evb sgpio master interface 2. The dts file should be configured as follows.

max-ngpios = <80>
ngpios = <64>

About the parameter naming, I was wondering if 'ngpios-of-sgpiom' is more clear
than max-ngpios as it is the maximum number of gpio pins that sgpio master
interfaces supported.

Yours,
Linus Walleij

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