Re: [PATCH] pinctrl/amd: fix masking of GPIO interrupts

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Mon, Oct 2, 2017 at 6:00 AM, Daniel Drake <drake@xxxxxxxxxxxx> wrote:

> On Asus laptop models X505BA, X505BP, X542BA and X542BP, the i2c-hid
> touchpad (using a GPIO for interrupts) becomes unresponsive after a
> few minutes of usage, or after placing two fingers on the touchpad,
> which seems to have the effect of queuing up a large amount of input
> data to be transferred.
>
> When the touchpad is in unresponsive state, we observed that the GPIO
> level-triggered interrupt is still at it's active level, however the
> pinctrl-amd driver is not receiving/dispatching more interrupts at this
> point.
>
> After the initial interrupt arrives, amd_gpio_irq_mask() is called
> however we then see amd_gpio_irq_handler() being called repeatedly for
> the same irq; the interrupt mask is not taking effect because of the
> following sequence of events:
>  - amd_gpio_irq_handler fires, reads and caches pin reg
>  - amd_gpio_irq_handler calls generic_handle_irq()
>  - During IRQ handling, amd_gpio_irq_mask() is called and modifies pin reg
>  - amd_gpio_irq_handler clears interrupt by writing cached value
>
> The stale cached value written at the final stage undoes the masking.
> Fix this by re-reading the register before clearing the interrupt.
>
> I also spotted that the interrupt-clearing code can race against
> amd_gpio_irq_mask() / amd_gpio_irq_unmask(), so add locking there.
> Presumably this race was leading to the loss of interrupts.
>
> After these changes, the touchpad appears to be working fine.
>
> Signed-off-by: Daniel Drake <drake@xxxxxxxxxxxx>

Patch applied for fixes with Nehal-bakulchandra's ACK.

Yours,
Linus Walleij
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