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Linux kernel for uConsole
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Michael Wu fdb0fb56ad gpiolib: fix incorrect IRQ requesting of an active-low lineevent 
commit 223ecaf140 upstream.

When a pin is active-low, logical trigger edge should be inverted to match
the same interrupt opportunity.

For example, a button pushed triggers falling edge in ACTIVE_HIGH case; in
ACTIVE_LOW case, the button pushed triggers rising edge. For user space the
IRQ requesting doesn't need to do any modification except to configuring
GPIOHANDLE_REQUEST_ACTIVE_LOW.

For example, we want to catch the event when the button is pushed. The
button on the original board drives level to be low when it is pushed, and
drives level to be high when it is released.

In user space we can do:

	req.handleflags = GPIOHANDLE_REQUEST_INPUT;
	req.eventflags = GPIOEVENT_REQUEST_FALLING_EDGE;

	while (1) {
		read(fd, &dat, sizeof(dat));
		if (dat.id == GPIOEVENT_EVENT_FALLING_EDGE)
			printf("button pushed\n");
	}

Run the same logic on another board which the polarity of the button is
inverted; it drives level to be high when pushed, and level to be low when
released. For this inversion we add flag GPIOHANDLE_REQUEST_ACTIVE_LOW:

	req.handleflags = GPIOHANDLE_REQUEST_INPUT |
		GPIOHANDLE_REQUEST_ACTIVE_LOW;
	req.eventflags = GPIOEVENT_REQUEST_FALLING_EDGE;

At the result, there are no any events caught when the button is pushed.
By the way, button releasing will emit a "falling" event. The timing of
"falling" catching is not expected.

Cc: stable@vger.kernel.org
Signed-off-by: Michael Wu <michael.wu@vatics.com>
Tested-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-08-06 19:06:54 +02:00
arch x86, boot: Remove multiple copy of static function sanitize_boot_params() 2019-08-06 19:06:53 +02:00
block block, scsi: Change the preempt-only flag into a counter 2019-08-04 09:30:57 +02:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: chacha20poly1305 - fix atomic sleep when using async algorithm 2019-07-26 09:14:19 +02:00
Documentation dt-bindings: allow up to four clocks for orion-mdio 2019-07-26 09:14:30 +02:00
drivers gpiolib: fix incorrect IRQ requesting of an active-low lineevent 2019-08-06 19:06:54 +02:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Btrfs: fix race leading to fs corruption after transaction abort 2019-08-06 19:06:53 +02:00
include uapi linux/coda_psdev.h: move upc_req definition from uapi to kernel side headers 2019-08-06 19:06:52 +02:00
init initramfs: free initrd memory if opening /initrd.image fails 2019-06-15 11:54:01 +02:00
ipc ipc/mqueue.c: only perform resource calculation if user valid 2019-08-06 19:06:52 +02:00
kernel kernel/module.c: Only return -EEXIST for modules that have finished loading 2019-08-06 19:06:47 +02:00
lib lib/test_string.c: avoid masking memset16/32/64 failures 2019-08-06 19:06:51 +02:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm/cma.c: fail if fixed declaration can't be honored 2019-08-06 19:06:51 +02:00
net ip_tunnel: allow not to count pkts on tstats by setting skb's dev to NULL 2019-08-04 09:30:57 +02:00
samples samples, bpf: suppress compiler warning 2019-07-14 08:11:04 +02:00
scripts kconfig: Clear "written" flag to avoid data loss 2019-08-06 19:06:53 +02:00
security selinux: fix empty write to keycreate file 2019-07-26 09:14:07 +02:00
sound ALSA: hda - Add a conexant codec entry to let mute led work 2019-07-31 07:27:11 +02:00
tools perf version: Fix segfault due to missing OPT_END() 2019-08-06 19:06:50 +02:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: arm/arm64: vgic: Fix kvm_device leak in vgic_its_destroy 2019-07-14 08:11:10 +02:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS platform/x86: Add Intel AtomISP2 dummy / power-management driver 2019-04-20 09:16:02 +02:00
Makefile kbuild: initialize CLANG_FLAGS correctly in the top Makefile 2019-08-06 19:06:53 +02:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.