Re: GPIOLIB locking is broken and how to fix it

[Aaro Koskinen <aaro.koskinen@xxxxxx>]

Hi,

On Tue, Dec 12, 2023 at 12:00:11PM +0100, Bartosz Golaszewski wrote:
> On Tue, Dec 12, 2023 at 11:12 AM Aaro Koskinen <aaro.koskinen@xxxxxx> wrote:
> > 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?

It's reading a register, then writing it back.

A.