PWM emulation with GPIO, build error

For Developers
1

Hi All,

We are planning to apply PWM emulation with GPIO feature to try on our device. We follow this page, but there are some build error I don't know how to fix it(I'm not familiar with kernel driver).
Error log are

  CC      drivers/pwm/pwm.o
drivers/pwm/pwm.c:508:3: error: 'struct class' has no member named 'dev_attrs'; did you mean 'class_attrs'?
  .dev_attrs = pwm_dev_attrs,
   ^~~~~~~~~
   class_attrs
drivers/pwm/pwm.c:508:15: error: initialization from incompatible pointer type [-Werror=incompatible-pointer-types]
  .dev_attrs = pwm_dev_attrs,
               ^~~~~~~~~~~~~
drivers/pwm/pwm.c:508:15: note: (near initialization for 'pwm_class.class_attrs')

Anyone can help me out? Thanks.

2

Hi All,

I fix the build error at pwm.c with following code.

  static DEVICE_ATTR(export, S_IRUGO | S_IWUSR, pwm_export_show, pwm_export_store);
  static DEVICE_ATTR(unexport, S_IWUSR, NULL, pwm_unexport_store);
  static DEVICE_ATTR(polarity, S_IRUGO | S_IWUSR, pwm_polarity_show, pwm_polarity_store);
  static DEVICE_ATTR(period_ns, S_IRUGO | S_IWUSR, pwm_period_ns_show, pwm_period_ns_store);
  static DEVICE_ATTR(duty_ns, S_IRUGO | S_IWUSR, pwm_duty_ns_show, pwm_duty_ns_store);
  static DEVICE_ATTR(tick_hz, S_IRUGO, pwm_tick_hz_show, NULL);
  static DEVICE_ATTR(run, S_IRUGO | S_IWUSR, pwm_run_show, pwm_run_store);
  
  static struct attribute *pwm_dev_attrs[] = {
      &dev_attr_export.attr,
      &dev_attr_unexport.attr,  
      &dev_attr_polarity.attr,
      &dev_attr_period_ns.attr,      
      &dev_attr_duty_ns.attr,
      &dev_attr_tick_hz.attr,
      &dev_attr_run.attr,                                    
      NULL
  };                                 
              
  static const struct attribute_group pwm_dev_attr_group = {
      .attrs = pwm_dev_attrs,
  };           
  
  static const struct attribute_group *pwm_dev_attr_groups[] = {
      &pwm_dev_attr_group,
      NULL                
  };
                              
  static struct class pwm_class = {
      .name       = "pwm",                 
      .owner      = THIS_MODULE,
      .dev_groups = pwm_dev_attr_groups,
  };

There is conflict build error.

drivers/built-in.o: In function `pwm_backlight_probe':
linux-4.9/drivers/video/backlight/pwm_bl.c:297: undefined reference to `devm_pwm_get'
linux-4.9/drivers/video/backlight/pwm_bl.c:297:(.text+0x137a4): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `devm_pwm_get'
drivers/built-in.o: In function `pwm_apply_args':
linux-4.9/./include/linux/pwm.h:605: undefined reference to `pwm_apply_state'
......
linux-4.9/./include/linux/pwm.h:407:(.text+0x13e24): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `pwm_apply_state'

Anyone can help? Thanks.

3

Hi all

I fix build on kernel part.
Before enable this driver, there is a folder /sys/class/pwm/pwmchip0.
After enable this driver pwmchip0 is gone? Why? Please help. Thanks.