linux: Disable hardware pwm when it is set to zero

Only write "1" to the "enable" file when a non-zero pwm width is
requested.  Write "0" to the "enable" file when a zero pwm width is
requested.

This fixes a problem on the replicape servo lines that prevented them
from being fully disabled.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

2 files changed, 12 insertions, 13 deletions

diff --git a/src/linux/gpio.h b/src/linux/gpio.h
index e6ef86bd..e2a39be0 100644
--- a/src/linux/gpio.h
+++ b/src/linux/gpio.h
@@ -37,7 +37,7 @@ void spi_transfer(struct spi_config config, uint8_t receive_data
                   , uint8_t len, uint8_t *data);
 
 struct gpio_pwm {
-    int fd;
+    int duty_fd, enable_fd;
     uint32_t period;
 };
 struct gpio_pwm gpio_pwm_setup(uint32_t pin, uint32_t cycle_time, uint16_t val);
diff --git a/src/linux/hard_pwm.c b/src/linux/hard_pwm.c
index cfe8b436..842776c6 100644
--- a/src/linux/hard_pwm.c
+++ b/src/linux/hard_pwm.c
@@ -77,20 +77,18 @@ struct gpio_pwm gpio_pwm_setup(uint32_t pin, uint32_t cycle_time, uint16_t val)
         report_errno("pwm duty_cycle", fd);
         goto fail;
     }
-
-    g.fd = fd;
-    gpio_pwm_write(g, val);
+    g.duty_fd = fd;
 
     // enable PWM
     snprintf(filename, sizeof(filename), pwm_path, chip_id, pwm_id, "enable");
     fd = open(filename, O_WRONLY|O_CLOEXEC);
     if (fd == -1) {
-        close(g.fd);
         report_errno("pwm enable", fd);
+        close(g.duty_fd);
         goto fail;
     }
-    write(fd, "1", 2);
-    close(fd);
+    g.enable_fd = fd;
+    gpio_pwm_write(g, val);
 
     return g;
 
@@ -103,12 +101,13 @@ fail:
 
 void gpio_pwm_write(struct gpio_pwm g, uint16_t val)
 {
+    if (!val) {
+        write(g.enable_fd, "0", 2);
+        return;
+    }
     char scratch[16];
     uint32_t duty_cycle = g.period * (uint64_t)val / MAX_PWM;
-    snprintf(scratch, sizeof(scratch), "%u", duty_cycle);
-    if (g.fd != -1) {
-        write(g.fd, scratch, strlen(scratch));
-    } else {
-        report_errno("pwm set duty_cycle", g.fd);
-    }
+    int len = snprintf(scratch, sizeof(scratch), "%u", duty_cycle);
+    write(g.duty_fd, scratch, len + 1);
+    write(g.enable_fd, "1", 2);
 }