Re: GPIOLIB locking is broken and how to fix it

[Bartosz Golaszewski <brgl@xxxxxxxx>]

On Tue, Dec 12, 2023 at 11:12 AM Aaro Koskinen <aaro.koskinen@xxxxxx> wrote:
>
> Hi,
>
> On Mon, Dec 11, 2023 at 04:49:43PM +0100, Bartosz Golaszewski wrote:
> > Aaro: do you still have the HW to test this driver?
>
> Yes, and I still use it.
>
> > I understand the need to disable interrupts during writing or reading
> > data - when we are driving the clock line. But do we also absolutely
> > need to hold the spinlock when setting the direction of the data line
> > to input? Because if we don't then we could modify the last remaining
> > offender to not set GPIO direction with a spinlock held and finally make
> > gpiod_direction_*() functions sleepable.
>
> Hmm, I think it's required to be able to provide atomic xfer function.
> That is needed for e.g. for power off.
>

By xfer: do you mean a request-response pair? Or just a single atomic,
one-way transfer of data?

Bart

> A.