linux-kernel - Question about SPIs' interrupt trigger type restrictions

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Date:   Wed, 25 May 2022 18:01:26 +0800
From:   richard clark <richard.xnu.clark@...il.com>
To:     maz@...nel.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Question about SPIs' interrupt trigger type restrictions

Hi Marc,

For below code snippet about SPI interrupt trigger type:

static int gic_set_type(struct irq_data *d, unsigned int type)
{
        ...
        /* SPIs have restrictions on the supported types */
        if ((range == SPI_RANGE || range == ESPI_RANGE) &&
            type != IRQ_TYPE_LEVEL_HIGH && type != IRQ_TYPE_EDGE_RISING)
                return -EINVAL;
        ...
}

We have a device at hand whose interrupt type is SPI, Falling edge
will trigger the interrupt. But the request_irq(50, handler,
IRQ_TYPE_EDGE_FALLING, ...) will return -EINVAL.

The question is, why must the SPI interrupt use IRQ_TYPE_EDGE_RISING
instead of IRQ_TYPE_EDGE_FALLING?

Thanks,