Re: [PATCH 2/2] gpio: sch: Add interrupt support

[Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>]

On Wed, Apr 24, 2019 at 02:41:02PM +0200, Jan Kiszka wrote:
> On 24.04.19 12:46, Mika Westerberg wrote:
> > On Wed, Apr 24, 2019 at 12:39:35PM +0200, Jan Kiszka wrote:
> > > On 24.04.19 12:33, Mika Westerberg wrote:
> > > > On Wed, Apr 24, 2019 at 12:19:02PM +0200, Jan Kiszka wrote:
> > > > > > I think what you want is "GPIO signaled ACPI event". It works so that
> > > > > > you declare _AEI method below the GPIO controller listing the GPIOs you
> > > > > > want to trigger events for and then either _Lxx, _Exx or _EVT method for
> > > > > > each of them under the same controller. GPIO core then handles it
> > > > > > automatically when you register the GPIO chip. See also
> > > > > > acpi_gpiochip_request_interrupts().
> > > > > 
> > > > > Right, that is was I read as well. Let's assume I would be able to patch the
> > > > > tables: Would I describe all the logic of this patch in ACPI terms? Where to
> > > > > enable interrupts, how to dispatch the SCI event, how to acknowledge it
> > > > > etc.? Will it also take care of locking? (BTW, my locking seems to have some
> > > > > remaining inconsistency, on second look.)
> > > > 
> > > > The GPIO core would then take care of it by requesting the GPIO in
> > > > question and dispatching to the correct event handler. In this patch you
> > > > just leave out the SCI part and only implement the irqchip like you did
> > > > already.
> > > 
> > > Could you point me to a gpio driver that works like that already? Would be
> > > easier to learn that from an example. That infrastructure with all its
> > > different modes is seriously complex and not very well documented.
> > 
> > Pretty much all drivers under drivers/pinctrl/intel.
> 
> OK... that's a purely descriptive way. So, provided we had such ACPI table
> entries, that plus some corresponding pinctrl driver would obsolete
> gpio-sch.c? Or are there other reason than historical ones for having
> gpio-*ch.c drivers around?

No they are for different hardware. The GPIO core will parse necessary
ACPI entires when any GPIO driver (with ACPI description) calls
gpiochip_add_data() or any of the wrappers.

> > > > > And even if that were possible, we would be back to the square of existing
> > > > > devices without those definitions. If this were a recent chipset, I would
> > > > > say, "go, fix future firmware versions". But this one is legacy.
> > > > 
> > > > Is it fixing some real issue with these legacy platforms? I mean without
> > > > the patch some GPE event is not handled properly? It was not clear to me
> > > > from the commit message.
> > > > 
> > > Without that patch, you are forced to poll for event changes in your
> > > application, timer-driven. There are application that cannot process these
> > > GPIOs because they lack such logic (mraa with node-red-node-intel-gpio is a
> > > public example).
> > 
> > But those are using the GPIOs via sysfs or the char device which should
> > work without the SCI handling part of your patch, no?
> 
> They work via sysfs. How would the char dev compensate the missing interrupt
> support?

I'm trying to say that for the sysfs access (well or char dev) you
should not need the sch_sci_handler() thing that is in your current
patch.