iio: stm32: fix adc/trigger link error

commit 6d745ee8b5e81f3a33791e3c854fbbfd6f3e585e upstream.

The ADC driver can trigger on either the timer or the lptim
trigger, but it only uses a Kconfig 'select' statement
to ensure that the first of the two is present. When the lptim
trigger is enabled as a loadable module, and the adc driver
is built-in, we now get a link error:

drivers/iio/adc/stm32-adc.o: In function `stm32_adc_get_trig_extsel':
stm32-adc.c:(.text+0x4e0): undefined reference to `is_stm32_lptim_trigger'

We could use a second 'select' statement and always have both
trigger drivers enabled when the adc driver is, but it seems that
the lptimer trigger was intentionally left optional, so it seems
better to keep it that way.

This adds a hack to use 'IS_REACHABLE()' rather than 'IS_ENABLED()',
which avoids the link error, but instead leads to the lptimer trigger
not being used in the broken configuration. I've added a runtime
warning for this case to help users figure out what they did wrong
if this should ever be done by accident.

Fixes: f0b638a7f6db ("iio: adc: stm32: add support for lptimer triggers")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/iio/timer/stm32-lptim-trigger.h b/include/linux/iio/timer/stm32-lptim-trigger.h
index 34d59bfdce2d2b12b0f6d7b61c601bfc0e2cb518..464458d20b16501ef45633c09cb2b7705e9f3f84 100644 (file)
--- a/include/linux/iio/timer/stm32-lptim-trigger.h
+++ b/include/linux/iio/timer/stm32-lptim-trigger.h
@@ -16,11 +16,14 @@
 #define LPTIM2_OUT     "lptim2_out"
 #define LPTIM3_OUT     "lptim3_out"
 
-#if IS_ENABLED(CONFIG_IIO_STM32_LPTIMER_TRIGGER)
+#if IS_REACHABLE(CONFIG_IIO_STM32_LPTIMER_TRIGGER)
 bool is_stm32_lptim_trigger(struct iio_trigger *trig);
 #else
 static inline bool is_stm32_lptim_trigger(struct iio_trigger *trig)
 {
+#if IS_ENABLED(CONFIG_IIO_STM32_LPTIMER_TRIGGER)
+       pr_warn_once("stm32 lptim_trigger not linked in\n");
+#endif
        return false;
 }
 #endif