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

Alex Elder
2020-05-26T11:53:27Z

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@linux.com>
>> ---
>> 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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