On Tue, Oct 3, 2017 at 7:09 PM, Doug Berger [off-list ref] wrote:

On 10/03/2017 06:55 PM, Gregory Fong wrote:

quoted

Hi Doug,

On Fri, Sep 29, 2017 at 8:40 PM, Doug Berger [off-list ref] wrote:

quoted

The basic memory-mapped GPIO controller lock must be released
before calling the registered GPIO interrupt handlers to allow
the interrupt handlers to access the hardware.  Otherwise, the
hardware accesses will deadlock when they attempt to grab the
lock.

I was having some trouble understanding exactly what the problem was
here, but I think I see it now.  Since this locks the entire bank,
where some GPIOs might be set as inputs and some as inputs (and
interrupt sources), then an interrupt on a GPIO that is supposed to
set another GPIO in the bank would result in deadlock.  Is that
correct?  If so, please update the commit message to make that clear,
and nice fix.  If not that, it would be nice to know what scenario can
cause a problem.

That is an example, but there are really many possibilities.

Basically, if a registered interrupt handler wants to access its GPIO
you are likely to run into trouble.  Another example might be an
interrupt that is configured to trigger on either edge transition and
the handler wants to know whether the input is currently high or low.

I can submit a V2 with a change in the description if you would like,
but I'm not sure what the clearest example would be.

If you could just mention both of these possible cases, that would be
great! With that change,

Acked-by: Gregory Fong <redacted>