To many interrupts from debug port rx line

Problem description

The serial RX line (PA9/DRXD) is set by Linux without the pull-up internal resistor. This could cause a lot of receiving interrupts from the debug serial port in noisy environments.

Solution

Change these lines in arch/arm/boot/dts/at91sam9x5dtsi:

Original

/* shared pinctrl settings */
dbgu {
    pinctrl_dbgu: dbgu-0 {
        atmel,pins =
            <AT91_PIOA 9 AT91_PERIPH_A AT91_PINCTRL_NONE        /* PA9 periph A */
             AT91_PIOA 10 AT91_PERIPH_A AT91_PINCTRL_PULL_UP>;  /* PA10 periph A with pullup */
    };
};

Changed

/* shared pinctrl settings */
dbgu {
    pinctrl_dbgu: dbgu-0 {
        atmel,pins =
            <AT91_PIOA 9 AT91_PERIPH_A AT91_PINCTRL_PULL_UP     /* PA9 periph A with pullup*/
             AT91_PIOA 10 AT91_PERIPH_A AT91_PINCTRL_PULL_UP>;  /* PA10 periph A with pullup */
    };
};

then compile the dts following this article:

• Build linux kernel