Re: [RFC PATCH v2 1/5] rtc: migrate driver data to RTC device

["Danilo Krummrich" <dakr@kernel.org>]

On Thu Jan 8, 2026 at 3:01 PM CET, Alexandre Belloni wrote:
> On 08/01/2026 14:52:08+0100, Danilo Krummrich wrote:
>> On Thu Jan 8, 2026 at 2:45 PM CET, Ke Sun wrote:
>> >
>> > On 1/8/26 19:12, Danilo Krummrich wrote:
>> >> On Wed Jan 7, 2026 at 3:37 PM CET, Ke Sun wrote:
>> >>> diff --git a/drivers/rtc/dev.c b/drivers/rtc/dev.c
>> >>> index baf1a8ca8b2b1..0f62ba9342e3e 100644
>> >>> --- a/drivers/rtc/dev.c
>> >>> +++ b/drivers/rtc/dev.c
>> >>> @@ -410,7 +410,7 @@ static long rtc_dev_ioctl(struct file *file,
>> >>>   		}
>> >>>   		default:
>> >>>   			if (rtc->ops->param_get)
>> >>> -				err = rtc->ops->param_get(rtc->dev.parent, &param);
>> >>> +				err = rtc->ops->param_get(&rtc->dev, &param);
>> >> It would make more sense to just pass a struct rtc_device than the embedded
>> >> struct device in the RTC callbacks.
>> > I considered passing struct rtc_device directly, but chose &rtc->dev
>> > to minimize changes to existing drivers, since most callbacks use
>> > dev_get_drvdata() on the device parameter.
>> 
>> No, you should not expose the embedded base device. For accessing the private
>> data you should add helpers like rtc_get_drvdata(). This is what other
>> subsystems do as well, e.g. [1].
>> 
>> [1] https://elixir.bootlin.com/linux/v6.18.3/source/include/linux/i2c.h#L371
>
> This is not a correct example as i2c is a bus, just like amba is...

Yes, struct i2c_client is indeed a bus device. However, the core struct device
is what holds the device private data commonly in the same way, regardless of
whether it is embedded in a bus or class device.

If you look for a class device example, here's PWM [2] and input [3].

[2] https://elixir.bootlin.com/linux/v6.18.3/source/include/linux/pwm.h#L382
[3] https://elixir.bootlin.com/linux/v6.18.3/source/include/linux/input.h#L388

> Actually, I don't think the rework is necessary at all or this would
> mean we need to rewor most of our existing subsystems.

That's not true, subsystems do not pass the parent device (i.e. the bus device)
through their class device callbacks exclusively.

- Danilo