libgpiod-scan: New example to for scanning devices

Summary: This examples supports a libgpiod client which scans
available devices/controllers on a platform to find which of
these supports a given GPIO line.

Signed-off-by: Faheem Sheikh <[email protected]>

libgpiod-scan/Makefile

@@ -0,0 +1,11 @@
+PROJ=libgpiod-scan
+SRC=main.c
+LIBS=-lgpiod
+
+CFLAGS=-Wall -Werror -O2
+CC?=cc
+all:
+	$(CC) $(SRC) $(LIBS) $(CFLAGS) -o $(PROJ)
+
+clean:
+	rm $(PROJ)

libgpiod-scan/README.md

@@ -0,0 +1,23 @@
+# libgpiod Scan Example
+
+This is a libgpiod client scanning all GPIO controllers for a given GPIO line.
+
+## Build
+```
+make
+```
+
+## Execute
+
+```
+./libgpiod-scan -n 10 -l 44
+```
+
+## Clean
+```
+make clean
+```
+
+## Wiring Example
+
+On a platform with multiple GPIO controllers, informs which one supports the given GPIO line

libgpiod-scan/main.c

@@ -0,0 +1,91 @@
+#include <gpiod.h>
+#include <ctype.h>
+#include <errno.h>
+#include <getopt.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+void banner(char *progName)
+{
+    printf("%s: \n", progName);
+    printf("     -u/h  : Usage message \n");
+    printf("     -n    : Number of GPIO controller to scan, Default range [0,1) \n");
+    printf("     -l    : Line number to search in GPIO controllers, Default 0 \n");
+}
+/* libgpiod client to scan all possible GPIO controller for a given GPIO Line */
+int main(int argc, char **argv)
+{
+
+    int optIn = 0;
+    int numDevices = -1;
+    int numLine = -1;
+
+    /* Boilerplate command line arguments processing */
+    while((optIn = getopt(argc, argv, "uhn:l:")) != EOF) {
+        switch(optIn) {
+            case 'u':
+            case 'h':
+                banner(argv[0]);
+                return 0;
+            case 'n':
+                numDevices = atoi(optarg);
+                break;
+            case 'l':
+                numLine = atoi(optarg);
+                break;
+            case '?':
+                if (optopt == 'c') {
+                    fprintf(stderr, "Option -%c supplied but number of devices not given.\n", optopt);
+                } else if (isprint(optopt)) {
+                    fprintf(stderr, "Unsupported option -%c supplied\n", optopt);
+                } else {
+                    fprintf(stderr, "Unknown option character 0x%x\n", optopt);
+                    return -1;
+                }
+            default:
+                banner(argv[0]);
+                return -1;
+        }
+    }
+
+    if (numDevices == -1) {
+        printf("Number of controllers not supplied, default value 1 will be used\n");
+        numDevices = 1;
+    }
+
+    if (numLine == -1) {
+        printf("GPIO Line number not specified, default value zero will be used\n");
+        numLine = 0;
+    }
+    printf("%s: started with GPIO controllers=%d to scan for GPIO Line=%d\n", argv[0], numDevices, numLine);
+
+    int chipIndex;
+    struct gpiod_chip *chip;
+    struct gpiod_line *line;
+    bool lineFound = false;
+    for (chipIndex = 0; chipIndex < numDevices; chipIndex++) {
+        chip = gpiod_chip_open_by_number(chipIndex);
+        if (!chip) {
+            fprintf(stderr, "Opening GPIO controller=%d failed with error=%d\n", chipIndex, errno);
+            continue;
+        } else {
+            line = gpiod_chip_get_line(chip, numLine);
+            if (!line) {
+                fprintf(stderr, "GPIO Line=%d not found in controller=%d\n", numLine, chipIndex);
+            } else {
+                printf("GPIO Line=%d found within controller=%d\n", numLine, chipIndex);
+                /* Break as soon as GPIO line within a controller is found */
+                lineFound = true;
+                gpiod_line_release(line);
+                gpiod_chip_close(chip);
+                break;
+            }
+
+            gpiod_chip_close(chip);
+        }
+    }
+
+    int retVal = lineFound ? 0 : -1;
+    return retVal;
+}