Makefile incorrectly set the flags for character device support

[fell-z]

Hey.

I had some issues using the lib via lua-periphery. After some digging of my own, I discovered that 'c-periphery' wasn't building with character device support, so I took a look at the Makefile and found a problem in the following line.

GPIO_CDEV_SUPPORT = $(if $(filter 1,$(GPIO_CDEV_V2_SUPPORT)),2,$(if $(filter 1,$(GPIO_CDEV_V1_SUPPORT)),1,0))

In those conditions, filter 1 should be filter 0 to work correctly.

[reeett]

Hi @fell-z, had the same problem writing a Makefile of lua-periphery for OpenWRT. Your suggestion fixed it for me too.

Thank you

---

Patchfile for OpenWRT 23.05.4

Index: lua-periphery-2.4.2/c-periphery/Makefile
===================================================================
--- lua-periphery-2.4.2.orig/c-periphery/Makefile
+++ lua-periphery-2.4.2/c-periphery/Makefile
@@ -12,7 +12,7 @@ OBJECTS = $(patsubst $(SRCDIR)/%.c,$(OBJ
 
 GPIO_CDEV_V1_SUPPORT := $(shell ! echo -e "#include <linux/gpio.h>\n#ifndef GPIO_GET_LINEEVENT_IOCTL\n#error\n#endif" | $(CC) -E - >/dev/null 2>&1; echo $$?)
 GPIO_CDEV_V2_SUPPORT := $(shell ! echo -e "#include <linux/gpio.h>\nint main(void) { GPIO_V2_LINE_FLAG_EVENT_CLOCK_REALTIME; return 0; }" | $(CC) -x c - >/dev/null 2>&1; echo $$?)
-GPIO_CDEV_SUPPORT = $(if $(filter 1,$(GPIO_CDEV_V2_SUPPORT)),2,$(if $(filter 1,$(GPIO_CDEV_V1_SUPPORT)),1,0))
+GPIO_CDEV_SUPPORT = $(if $(filter 0,$(GPIO_CDEV_V2_SUPPORT)),2,$(if $(filter 0,$(GPIO_CDEV_V1_SUPPORT)),1,0))
 
 COMMIT_ID := $(shell git describe --abbrev --always --tags --dirty 2>/dev/null || echo "")
 

[vsergeev]

If you're seeing 0 for GPIO_CDEV_V1_SUPPORT or GPIO_CDEV_V2_SUPPORT, that means there was an error in building the support test, so there might be a problem with those tests on some platforms.

$(shell ! ...; echo $$?) inverts the status code, so if the support test succeeded, i.e. exited 0, then the variable will evaluate to 1.

$(if $(filter 1,$(GPIO_CDEV_V2_SUPPORT)),2,$(if $(filter 1,$(GPIO_CDEV_V1_SUPPORT)),1,0)) evaluates to 2 if GPIO_CDEV_V2_SUPPORT is 1, to 1 if GPIO_CDEV_V1_SUPPORT is 1, and otherwise 0.

Changing it to $(if $(filter 0 ... will make it succeed and indicate v2 support, but only for a failing a support test...

Probably the most useful info would be the output of echo -e "#include <linux/gpio.h>\n#ifndef GPIO_GET_LINEEVENT_IOCTL\n#error\n#endif" | $(CC) -E - on one of these platforms where the support test is failing.