Re: [greybus-dev] [PATCH 1/8] driver core: Add helper for accessing Power Management callbacs

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On 5/26/20 1:33 AM, Greg Kroah-Hartman wrote:
On Mon, May 25, 2020 at 06:26:01PM +0000, Krzysztof Wilczyński wrote:
Add driver_to_pm() helper allowing for accessing the Power Management
callbacs for a particular device.  Access to the callbacs (struct
dev_pm_ops) is normally done through using the pm pointer that is
embedded within the device_driver struct.

Helper allows for the code required to reference the pm pointer and
access Power Management callbas to be simplified.  Changing the
following:

   struct device_driver *drv = dev->driver;
   if (dev->driver && dev->driver->pm && dev->driver->pm->prepare) {
       int ret = dev->driver->pm->prepare(dev);

To:

   const struct dev_pm_ops *pm = driver_to_pm(dev->driver);
   if (pm && pm->prepare) {
       int ret = pm->prepare(dev);

Or, changing the following:

      const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;

To:
      const struct dev_pm_ops *pm = driver_to_pm(dev->driver);

Signed-off-by: Krzysztof Wilczyński <kw@xxxxxxxxx>
---
  include/linux/device/driver.h | 15 +++++++++++++++
  1 file changed, 15 insertions(+)

diff --git a/include/linux/device/driver.h b/include/linux/device/driver.h
index ee7ba5b5417e..ccd0b315fd93 100644
--- a/include/linux/device/driver.h
+++ b/include/linux/device/driver.h
@@ -236,6 +236,21 @@ driver_find_device_by_acpi_dev(struct device_driver *drv, const void *adev)
  }
  #endif
+/**
+ * driver_to_pm - Return Power Management callbacs (struct dev_pm_ops) for
+ *                a particular device.
+ * @drv: Pointer to a device (struct device_driver) for which you want to access
+ *       the Power Management callbacks.
+ *
+ * Returns a pointer to the struct dev_pm_ops embedded within the device (struct
+ * device_driver), or returns NULL if Power Management is not present and the
+ * pointer is not valid.
+ */
+static inline const struct dev_pm_ops *driver_to_pm(struct device_driver *drv)
+{
+	return drv && drv->pm ? drv->pm : NULL;

This could just be:

	if (drv)
		return drv->pm;

	return NULL;

Or if you want to evoke passion in Greg:

	return drv ? drv->pm : NULL;

					-Alex

I hate ? : lines with a passion, as they break normal pattern mattching
in my brain.  Please just spell this all out:
	if (drv && drv->pm)
		return drv->pm;
	return NULL;

Much easier to read, and the compiler will do the exact same thing.

Only place ? : are ok to use in my opinion, are as function arguments.

thanks,

greg k-h
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