On středa 21. února 2018 8:11:25 CET, Alexander Stein wrote:
Well, that is the exact situation on the board I had to deal
with. The MCP was
attached to a transisitor inverting the signal. The output on MCP has to be
push-pull as there was no pull-up oder -down. But the line connecting the
inverter to the CPU was an open-drain one and this line was
actually a shared
IRQ line. So of course the line bewteen MCP and inverter cannot
be shared, but
the IRQ used on CPU is actually shared. How can this be respresented in DT?
What I propose is to have it like this:
gpio@1 {
compatible = "microchip,mcp23s17";
irq-active-high;
interrupt-parent = <&gpio0>;
interrupts = <123 IRQ_TYPE_LEVEL_LOW>;
// ...
};
In other words, the "interrupt-parent" and "interrupts" DT statements
specify how the upstream interrupt controller should be set up, while other
properties define settings of the IRQ source.
But as Phil points out, such a change would break the DT ABI. This means
that we should preserve the semantics of any existing DT. We can do that by
introducing another property. Here's a rough sketch:
#define MCP23S08_IRQ_OPEN_DRAIN 1
#define MCP23S08_IRQ_PUSH_PULL_ACTIVE_LOW 2
#define MCP23S08_IRQ_PUSH_PULL_ACTIVE_HIGH 3
irqflags = IRQF_SHARED | IRQF_ONESHOT;
if (new_irq_mode != -1) {
/* irqflags are only set to IRQF_SHARED | IRQF_ONESHOT,
nothing else */
} else if (irq_active_high) {
/* an existing property */
irqflags |= IRQF_ACTIVE_HIGH;
} else {
irqflags |= IRQF_ACTIVE_LOW;
}
A "new-style" DT then should look like this for your scenario with an
electrical invertor:
gpio@1 {
compatible = "microchip,mcp23s17";
irq-mode = MCP23S08_IRQ_PUSH_PULL_ACTIVE_HIGH;
interrupt-parent = <&gpio0>;
interrupts = <123 IRQ_TYPE_LEVEL_LOW>;
// ...
};
A downside of this approach is that it's using a custom enum, not a
standard property like drive-open-drain. Pick your poison.
Cheers,
Jan
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