linux-kernel - Re: [PATCH 3/4] rtc: Introduce devm_rtc_allocate_device

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Message-ID: <bf81200d-4a08-4ed3-b67b-d2cb1c1df2dd@stanley.mountain>
Date: Tue, 21 Jan 2025 18:15:43 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Peng Fan <peng.fan@....com>
Cc: "Peng Fan (OSS)" <peng.fan@....nxp.com>,
	Sudeep Holla <sudeep.holla@....com>,
	Cristian Marussi <cristian.marussi@....com>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	"arm-scmi@...r.kernel.org" <arm-scmi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>
Subject: Re: [PATCH 3/4] rtc: Introduce devm_rtc_allocate_device_priv

On Tue, Jan 21, 2025 at 02:35:59PM +0000, Peng Fan wrote:
> Hi Dan,
> 
> > Subject: Re: [PATCH 3/4] rtc: Introduce devm_rtc_allocate_device_priv
> > 
> > On Mon, Jan 20, 2025 at 10:25:35AM +0800, Peng Fan (OSS) wrote:
> > >  int __devm_rtc_register_device(struct module *owner, struct
> > > rtc_device *rtc) diff --git a/drivers/rtc/dev.c b/drivers/rtc/dev.c
> > > index
> > >
> > c4a3ab53dcd4b7280a3a2981fe842729603a1feb..e0e1a488b795645d
> > 7c9453490d6c
> > > dba510cc5db5 100644
> > > --- a/drivers/rtc/dev.c
> > > +++ b/drivers/rtc/dev.c
> > > @@ -410,7 +410,8 @@ 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->priv ?
> > > +							  &rtc->dev :
> > rtc->dev.parent, &param);
> > 
> > This seems kind of horrible...  I can't think of anywhere else which does
> > something like this.
> > 
> > It would almost be better to do something like:
> > 
> > 	err = rtc->ops->param_get(rtc->priv ? (void *)rtc : rtc-
> > >dev.parent, &param);
> > 
> > The advatange of this is that it looks totally horrible from the get go
> > instead of only subtly wrong.  And it would immediately crash if you
> > got it wrong implementing the ->param_get() function pointer.
> 
> Thanks for help improving the code. I will include this in V2 and post
> out after we reach a goal on how to support the 2nd RTC on i.MX95.

Don't do what I said actually...  Let's find a better way.  I don't
know why rtc_class_ops function pointers take a device pointer instead
of an rtc_device pointer.  Or if they did take a device pointer why
not the &rtc->dev like you suggested?  But let's not do both like this.

Migrating all the function pointers is a lot of work but not impossible.

regards,
dan carpenter