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: >> [...] >>> +What: /sys/class/pwm/pwmchipN/pwmX/duty >>> +Date: May 2013 >>> +KernelVersion: 3.11 >>> +Contact: H Hartley Sweeten <hsweeten@xxxxxxxxxxxxxxxxxxx> >>> +Description: >>> + Sets the PWM duty cycle in nanoseconds. >> >> Sorry, I should've been more specific before. I'd like this to be named >> duty_cycle. We now have the pwm_{set,get}_duty_cycle() accessors and I'd >> like to eventually use the spelled-out form consistently. Ok. I'll change this. >>> +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. >> >> In order not to burden you with too much work, one option for now would >> be to unconditionally build the sysfs.c file and use something along >> these lines in pwmchip_sysfs_{,un}export(): >> >> if (!IS_ENABLED(CONFIG_PWM_SYSFS)) >> return; >> >> Which should allow the compiler to throw away all PWM_SYSFS-related >> code in that file, leaving an empty function. > > > Won't that also cause the compiler to spew a bunch of warnings about > unreachable code in the !CONFIG_PWM_SYSFS case? We have the > unreachable() macro, but that isn't supported nicely by all compilers. > > If CONFIG_SYSFS is not enabled and sysfs.c is using functions that now > do not exist, that will cause compile errors, since the compiler will > still attempt to compile all of the code, even though it will remove > most of it after doing so. > > Also, any functions that are extern will also end up generating empty > functions in the kernel binary (static linkage functions should > disappear completely). This is obviously very negligible in size, > but using a proper Kconfig option results in zero size if the option > is compiled out. > >> It's not the optimal >> solution, which would require the sysfs code to go into core.c and be >> conditionalized there, but it's good enough. I can always go and clean >> up that code later (maybe doing the same for DEBUG_FS while at it). >> >> The big advantage of this is that we get full compile coverage of the >> sysfs interface, whether it's enabled or not. Calling an empty function >> once when the chip is registered is an acceptable overhead. > > Why not just make CONFIG_PWM_SYSFS default y, so that if CONFIG_SYSFS is > enabled (which should be true for the vast majority of test configs) that > pwm sysfs is also enabled? > > The IS_ENABLED method just seems very messy for a very small gain. 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 #ifdef CONFIG_SYSFS void pwmchip_sysfs_export(struct pwm_chip *chip); void pwmchip_sysfs_unexport(struct pwm_chip *chip); #else static inline void pwmchip_sysfs_export(struct pwm_chip *chip) { } static inline void pwmchip_sysfs_unexport(struct pwm_chip *chip) { } #endif /* CONFIG_SYSFS */ So, no IS_ENABLED or #ifdef'ery in the source file. I'll make the change and post a v5 shortly. Regards, Hartley -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html