| Message ID | 20250410-open-drain-source-tests-v1-1-a062d2280cc5@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [libgpiod] tests: uapi: add test-cases for open-drain and open-source emulation | expand |
On Thu, Apr 10, 2025 at 12:17 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote: > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > The kernel GPIO subsystem can emulate open-drain and open-source by not > actively driving the line for active and inactive output values > respectively. The kernel does it by setting the line to input in these > cases but this still must be reported as output to user-space. Add new > test-cases that verify this behavior. Thanks, that's indeed a good idea! Reviewed-by: Andy Shevchenko <andy@kernel.org>
On Thu, Apr 10, 2025 at 11:17:47AM +0200, Bartosz Golaszewski wrote: > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > The kernel GPIO subsystem can emulate open-drain and open-source by not > actively driving the line for active and inactive output values > respectively. The kernel does it by setting the line to input in these > cases but this still must be reported as output to user-space. Add new > test-cases that verify this behavior. > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > --- > Andy's comment on a GPIOLIB patch made me realize it's a good idea to > add tests for open-drain and open-source emulation in the kernel where > we don't actively drive the line for active and inactive values > respectively. > --- > tests/tests-kernel-uapi.c | 87 +++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 87 insertions(+) > > diff --git a/tests/tests-kernel-uapi.c b/tests/tests-kernel-uapi.c > index ff220fc..5955fac 100644 > --- a/tests/tests-kernel-uapi.c > +++ b/tests/tests-kernel-uapi.c > @@ -110,3 +110,90 @@ GPIOD_TEST_CASE(enable_debounce_then_edge_detection) > > g_assert_cmpuint(ts_falling, >, ts_rising); > } > + > +GPIOD_TEST_CASE(open_drain_emulation) > +{ > + static const guint offset = 2; > + > + g_autoptr(GPIOSimChip) sim = g_gpiosim_chip_new("num-lines", 8, NULL); > + g_autoptr(struct_gpiod_chip) chip = NULL; > + g_autoptr(struct_gpiod_line_settings) settings = NULL; > + g_autoptr(struct_gpiod_line_config) line_cfg = NULL; > + g_autoptr(struct_gpiod_line_request) request = NULL; > + g_autoptr(struct_gpiod_line_info) info = NULL; > + gint ret; > + > + chip = gpiod_test_open_chip_or_fail(g_gpiosim_chip_get_dev_path(sim)); > + settings = gpiod_test_create_line_settings_or_fail(); > + line_cfg = gpiod_test_create_line_config_or_fail(); > + > + gpiod_line_settings_set_direction(settings, > + GPIOD_LINE_DIRECTION_OUTPUT); > + gpiod_line_settings_set_drive(settings, GPIOD_LINE_DRIVE_OPEN_DRAIN); > + gpiod_test_line_config_add_line_settings_or_fail(line_cfg, &offset, 1, > + settings); > + request = gpiod_test_chip_request_lines_or_fail(chip, NULL, line_cfg); > + > + ret = gpiod_line_request_set_value(request, offset, > + GPIOD_LINE_VALUE_ACTIVE); > + g_assert_cmpint(ret, ==, 0); > + gpiod_test_return_if_failed(); > + > + /* > + * The open-drain emulation in the kernel will set the line's direction > + * to input but NOT set FLAG_IS_OUT. Let's verify the direction is > + * still reported as output. > + */ My understanding is that FLAG_IS_OUT is always set for output lines, even if the direction is set to input for the emulation. To quote gpiod_direction_output(): set_output_flag: /* * When emulating open-source or open-drain functionalities by not * actively driving the line (setting mode to input) we still need to * set the IS_OUT flag or otherwise we won't be able to set the line * value anymore. */ if (ret == 0) set_bit(FLAG_IS_OUT, &desc->flags); return ret; Cheers, Kent.
On Fri, 11 Apr 2025 at 03:34, Kent Gibson <warthog618@gmail.com> wrote: > > On Thu, Apr 10, 2025 at 11:17:47AM +0200, Bartosz Golaszewski wrote: > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > The kernel GPIO subsystem can emulate open-drain and open-source by not > > actively driving the line for active and inactive output values > > respectively. The kernel does it by setting the line to input in these > > cases but this still must be reported as output to user-space. Add new > > test-cases that verify this behavior. > > > > + ret = gpiod_line_request_set_value(request, offset, > > + GPIOD_LINE_VALUE_ACTIVE); > > + g_assert_cmpint(ret, ==, 0); > > + gpiod_test_return_if_failed(); > > + > > + /* > > + * The open-drain emulation in the kernel will set the line's direction > > + * to input but NOT set FLAG_IS_OUT. Let's verify the direction is > > + * still reported as output. > > + */ > > My understanding is that FLAG_IS_OUT is always set for output lines, > even if the direction is set to input for the emulation. > Of course, it's a typo. It should have said: does NOT clear FLAG_IS_OUT. Bartosz
diff --git a/tests/tests-kernel-uapi.c b/tests/tests-kernel-uapi.c index ff220fc..5955fac 100644 --- a/tests/tests-kernel-uapi.c +++ b/tests/tests-kernel-uapi.c @@ -110,3 +110,90 @@ GPIOD_TEST_CASE(enable_debounce_then_edge_detection) g_assert_cmpuint(ts_falling, >, ts_rising); } + +GPIOD_TEST_CASE(open_drain_emulation) +{ + static const guint offset = 2; + + g_autoptr(GPIOSimChip) sim = g_gpiosim_chip_new("num-lines", 8, NULL); + g_autoptr(struct_gpiod_chip) chip = NULL; + g_autoptr(struct_gpiod_line_settings) settings = NULL; + g_autoptr(struct_gpiod_line_config) line_cfg = NULL; + g_autoptr(struct_gpiod_line_request) request = NULL; + g_autoptr(struct_gpiod_line_info) info = NULL; + gint ret; + + chip = gpiod_test_open_chip_or_fail(g_gpiosim_chip_get_dev_path(sim)); + settings = gpiod_test_create_line_settings_or_fail(); + line_cfg = gpiod_test_create_line_config_or_fail(); + + gpiod_line_settings_set_direction(settings, + GPIOD_LINE_DIRECTION_OUTPUT); + gpiod_line_settings_set_drive(settings, GPIOD_LINE_DRIVE_OPEN_DRAIN); + gpiod_test_line_config_add_line_settings_or_fail(line_cfg, &offset, 1, + settings); + request = gpiod_test_chip_request_lines_or_fail(chip, NULL, line_cfg); + + ret = gpiod_line_request_set_value(request, offset, + GPIOD_LINE_VALUE_ACTIVE); + g_assert_cmpint(ret, ==, 0); + gpiod_test_return_if_failed(); + + /* + * The open-drain emulation in the kernel will set the line's direction + * to input but NOT set FLAG_IS_OUT. Let's verify the direction is + * still reported as output. + */ + info = gpiod_test_chip_get_line_info_or_fail(chip, offset); + g_assert_cmpint(gpiod_line_info_get_direction(info), ==, + GPIOD_LINE_DIRECTION_OUTPUT); + g_assert_cmpint(gpiod_line_info_get_drive(info), ==, + GPIOD_LINE_DRIVE_OPEN_DRAIN); + + /* + * The actual line is not being actively driven, so check that too on + * the gpio-sim end. + */ + g_assert_cmpint(g_gpiosim_chip_get_value(sim, offset), ==, + G_GPIOSIM_VALUE_INACTIVE); +} + +GPIOD_TEST_CASE(open_source_emulation) +{ + static const guint offset = 2; + + g_autoptr(GPIOSimChip) sim = g_gpiosim_chip_new("num-lines", 8, NULL); + g_autoptr(struct_gpiod_chip) chip = NULL; + g_autoptr(struct_gpiod_line_settings) settings = NULL; + g_autoptr(struct_gpiod_line_config) line_cfg = NULL; + g_autoptr(struct_gpiod_line_request) request = NULL; + g_autoptr(struct_gpiod_line_info) info = NULL; + gint ret; + + chip = gpiod_test_open_chip_or_fail(g_gpiosim_chip_get_dev_path(sim)); + settings = gpiod_test_create_line_settings_or_fail(); + line_cfg = gpiod_test_create_line_config_or_fail(); + + gpiod_line_settings_set_direction(settings, + GPIOD_LINE_DIRECTION_OUTPUT); + gpiod_line_settings_set_drive(settings, GPIOD_LINE_DRIVE_OPEN_SOURCE); + gpiod_test_line_config_add_line_settings_or_fail(line_cfg, &offset, 1, + settings); + request = gpiod_test_chip_request_lines_or_fail(chip, NULL, line_cfg); + + ret = gpiod_line_request_set_value(request, offset, + GPIOD_LINE_VALUE_INACTIVE); + g_assert_cmpint(ret, ==, 0); + gpiod_test_return_if_failed(); + + /* + * The open-source emulation in the kernel will set the line's direction + * to input but NOT set FLAG_IS_OUT. Let's verify the direction is + * still reported as output. + */ + info = gpiod_test_chip_get_line_info_or_fail(chip, offset); + g_assert_cmpint(gpiod_line_info_get_direction(info), ==, + GPIOD_LINE_DIRECTION_OUTPUT); + g_assert_cmpint(gpiod_line_info_get_drive(info), ==, + GPIOD_LINE_DRIVE_OPEN_SOURCE); +}