On Tuesday, June 11, 2013 11:35 AM, Thierry Reding wrote: > On Tue, Jun 11, 2013 at 11:47:23AM -0500, H Hartley Sweeten wrote: >> On Tuesday, June 11, 2013 9:09 AM, H Hartley Sweeten wrote: >>> On Tuesday, June 11, 2013 4:29 AM, Ryan Mallon wrote: >>>> On 11/06/13 20:14, Thierry Reding wrote: >>>>> On Mon, Jun 10, 2013 at 04:12:07PM -0700, H Hartley Sweeten wrote: >>>>>> +config PWM_SYSFS >>>>>> + bool "/sys/class/pwm/... (sysfs interface)" >>>>>> + depends on SYSFS >>>>>> + help >>>>>> + Say Y here to provide a sysfs interface to control PWMs. >>>>>> + >>>>>> + For every instance of a PWM device there is a pwmchipN >>>>>> directory >>>>>> + created in /sys/class/pwm. Use the export attribute to request >>>>>> + a PWM to be accessible from userspace and the unexport >>>>>> attribute >>>>>> + to return the PWM to the kernel. Each exported PWM will have a >>>>>> + pwmX directory in the pwmchipN it is associated with. >>>>> >>>>> I have a small quibble with this. Introducing options like this make it >>>>> increasingly difficult to compile-test all the various combinations, so >>>>> I'd like to see this converted to a form that will play well with the >>>>> IS_ENABLED() macro. We already have the same issue with DEBUG_FS, only >>>>> to a lesser degree because it doesn't have an additional PWM-specific >>>>> Kconfig option. >>> >>> How about removing the Kconfig option and just doing: >>> >>> obj-$(CONFIG_SYSFS) += sysfs.o >>> >>> This way the PWM sysfs interface is always compiled and included in the >>> build >>> as long as CONFIG_SYSFS is enabled. The check in the header would change to >> >> That didn't work. As Ryan pointed out we get undefined references due to >> sysfs.c being compiled but not core.c when CONFIG_PWM is not enabled. > > Why not add dummies for the missing functions? It was my impression that > we had dummies for all of them already, but if not they should certainly > be added to match what other subsystems do.
I just looked it over and the undefined reference was for pwm_set_polarity(). The dummy for that function is missing. The other problem with this approach is the sysfs.c file gets compiled whenever CONFIG_SYSFS is enabled even if CONFIG_PWM is not enabled. Hartley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
