On 12.08.2014 12:01, Mika Westerberg wrote:
On Fri, Aug 08, 2014 at 02:36:02PM +0200, Linus Walleij wrote:
On Thu, Jul 24, 2014 at 5:51 PM, Tomasz Nowicki
<tomasz.nowicki@xxxxxxxxxx> wrote:
GPIO signaled events is quite new thing in Linux kernel.
AFAIK, there are not many board which can take advantage of it.
However, GPIO events are very useful feature during work on ACPI
subsystems.
Overall this seems like a pretty nice debug feature.
This commit emulates GPIO h/w behaviour and consists on read/write
operation to debugfs file. GPIO device instance is still required in DSDT
table along with _AEI resources and event methods.
Reading from file provides pin to GPIO device map e.g. :
$ cat /sys/kernel/debug/acpi/gpio_event
GPIO device name: /__SB.GPI0
Available GPIO pin map:
/__SB.GPI0 <-> pin 0x100
Based on that, user can trigger method corresponding to device pin number:
$ echo "/__SB.GPI0 0x100" > /sys/kernel/debug/acpi/gpio_event
I need input from Rafael and Mika as to whether this is a
good interface.
Maybe it would make sense to move this into drivers/gpio/gpiolib-acpi.c
and hide it behind some Kconfig entry?
Since you already need to have DSDT/SSDT table for this to provide the
GPIO device, _AEI and the event methods, I would rather make it so that
acpi_gpiochip_request_interrupt() will add debugfs entry for each GPIO
it finds in _AEI, like:
/sys/kernel/debug/acpi/events/<GPIO DEVICE>/n
And you could trigger it by writing '1' or something like that to that
file.
Thanks for comments. The idea of available gpio events list under
/sys/kernel/debug/acpi/events/<GPIO DEVICE>/n is worth adding.
However, acpi_gpiochip_request_interrupt() would be called if we would
have real GPIO H/W and related driver. Initial idea of this patch was to
avoid that restriction. So there are two cases:
1. If we have GPIO chip, it is already described in DSDT/SSDT and using
this patch, user could trigger events by software too.
2. None of GPIO chip, so we need to add GPIO/_AEI etc. descrition to
DSDT/SSDT and pretend we have GPIO chip on board.
Regards,
Tomasz Nowicki
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