Re: [PATCH] gpio: gpio-omap: fix level interrupt idling

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Fri, Mar 1, 2019 at 8:03 PM Tony Lindgren <tony@xxxxxxxxxxx> wrote:

> From: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
>
> Tony notes that the GPIO module does not idle when level interrupts are
> in use, as the wakeup appears to get stuck.
>
> After extensive investigation, it appears that the wakeup will only be
> cleared if the interrupt status register is cleared while the interrupt
> is enabled. However, we are currently clearing it with the interrupt
> disabled for level-based interrupts.
>
> It is acknowledged that this observed behaviour conflicts with a
> statement in the TRM:
>
> CAUTION
>   After servicing the interrupt, the status bit in the interrupt status
>   register (GPIOi.GPIO_IRQSTATUS_0 or GPIOi.GPIO_IRQSTATUS_1) must be
>   reset and the interrupt line released (by setting the corresponding
>   bit of the interrupt status register to 1) before enabling an
>   interrupt for the GPIO channel in the interrupt-enable register
>   (GPIOi.GPIO_IRQSTATUS_SET_0 or GPIOi.GPIO_IRQSTATUS_SET_1) to prevent
>   the occurrence of unexpected interrupts when enabling an interrupt
>   for the GPIO channel.
>
> However, this does not appear to be a practical problem.
>
> Further, as reported by Grygorii Strashko <grygorii.strashko@xxxxxx>,
> the TI Android kernel tree has an earlier similar patch as "GPIO: OMAP:
> Fix the sequence to clear the IRQ status" saying:
>
>  if the status is cleared after disabling the IRQ then sWAKEUP will not
>  be cleared and gates the module transition
>
> When we unmask the level interrupt after the interrupt has been handled,
> enable the interrupt and only then clear the interrupt. If the interrupt
> is still pending, the hardware will re-assert the interrupt status.
>
> Should the caution note in the TRM prove to be a problem, we could
> use a clear-enable-clear sequence instead.
>
> Cc: Aaro Koskinen <aaro.koskinen@xxxxxx>
> Cc: Grygorii Strashko <grygorii.strashko@xxxxxx>
> Cc: Keerthy <j-keerthy@xxxxxx>
> Cc: Peter Ujfalusi <peter.ujfalusi@xxxxxx>
> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
> [tony@xxxxxxxxxxx: updated comments based on an earlier TI patch]
> Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx>

Patch applied! Really nice debugging here.

Yours,
Linus Walleij