[PATCH] iio: stm32: fix adc/trigger link error

On Wed, 6 Sep 2017 18:16:33 +0200
Fabrice Gasnier [off-list ref] wrote:

On 09/06/2017 02:56 PM, Arnd Bergmann wrote:

quoted

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.  

Hi Arnd,

This is correct, not all stm32 have this hardware.

quoted

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>  

Tested-by: Fabrice Gasnier <redacted>

This may take me a few weeks to pick up.  I don't want to
pull the mfd immutable branch in just to have this fix, so this will
get sorted after rc1 is out.

As ever, poke me if it looks like I've forgotten about it.
Sorry for the delay!

Jonathan

Many thanks for the fix,
Best Regards,
Fabrice

quoted

---
 include/linux/iio/timer/stm32-lptim-trigger.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/iio/timer/stm32-lptim-trigger.h b/include/linux/iio/timer/stm32-lptim-trigger.h
index 34d59bfdce2d..464458d20b16 100644
--- 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
  

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