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    SubjectRe: [PATCH 1/2] gpio: Add a driver for Cadence GPIO controller
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    Hi Boris, Linus,

    On 30/03/17 12:29, Boris Brezillon wrote:
    > Hi Linus,
    >
    > On Thu, 30 Mar 2017 11:03:45 +0200
    > Linus Walleij <linus.walleij@linaro.org> wrote:
    >
    >> On Wed, Mar 29, 2017 at 6:04 PM, Boris Brezillon
    >> <boris.brezillon@free-electrons.com> wrote:
    >>
    >>> Add a driver for Cadence GPIO controller.
    >> IIUC Cadence do a lot of things. Are there variants of this controller?
    > I'll let Simon answer that one.
    This is a controller that has been around since 2000. It is not
    configurable in any way, so there are no variants. Cadence do not offer
    any other GPIO controllers as IP.
    >>> +static irqreturn_t cdns_gpio_irq_handler(int irq, void *dev)
    >>> +{
    >>> + struct cdns_gpio_chip *cgpio = dev;
    >>> + unsigned long status;
    >>> + int hwirq;
    >>> +
    >>> + /*
    >>> + * FIXME: If we have an edge irq that is masked we might lose it
    >>> + * since reading the STATUS register clears all IRQ flags.
    >>> + * We could store the status of all masked IRQ in the cdns_gpio_chip
    >>> + * struct but we then have no way to re-trigger the interrupt when
    >>> + * it is unmasked.
    >>> + */
    >> It is marked FIXME but do you think it can even be fixed? It seems
    >> like a hardware flaw. :(
    > Maybe not. Unless Simon comes up with a magic register to re-trigger an
    > interrupt :-).
    There are no plans to update the controller.
    > Another solution would be to write 0xffffffff into CDNS_GPIO_OUTPUT_EN
    > at probe time so that each time CDNS_GPIO_DIRECTION_MODE is modified to
    > set a pin in output mode, the CDNS_GPIO_OUTPUT_EN is already correctly
    > configured.
    > Simon, would that work? Is there a good reason to keep a bit in
    > CDNS_GPIO_OUTPUT_EN set to 0 when the GPIO is in input mode (power
    > consumption?)?
    If direction_mode is set to input then output_en is ignored so this
    should work. The hardware defaults to output mode, so as long as you
    set all pins to input mode before you set all output_en bits there
    should be no negative effect.

    Cheers,
    -- Simon

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