Re: [PATCH 04/10] rtc: at91rm9200: use of_platform_populate as return value

From: Jonathan Cameron <jic23@kernel.org>
To: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Eugen.Hristev@microchip.com, robh+dt@kernel.org,
	Nicolas.Ferre@microchip.com, linux-iio@vger.kernel.org,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-rtc@vger.kernel.org,
	a.zummo@towertech.it, Ludovic.Desroches@microchip.com
Subject: Re: [PATCH 04/10] rtc: at91rm9200: use of_platform_populate as return value
Date: Mon, 23 Dec 2019 11:16:36 +0000	[thread overview]
Message-ID: <20191223111636.4698123b@archlinux> (raw)
In-Reply-To: <20191219102321.GR695889@piout.net>

On Thu, 19 Dec 2019 11:23:21 +0100
Alexandre Belloni <alexandre.belloni@bootlin.com> wrote:

> On 19/12/2019 09:15:02+0000, Eugen.Hristev@microchip.com wrote:
> > 
> > 
> > On 18.12.2019 18:58, Alexandre Belloni wrote:  
> > > On 18/12/2019 16:52:21+0000, Eugen.Hristev@microchip.com wrote:  
> > >>
> > >>
> > >> On 18.12.2019 18:43, Alexandre Belloni wrote:
> > >>  
> > >>> Hi,
> > >>>
> > >>> On 18/12/2019 16:24:00+0000, Eugen.Hristev@microchip.com wrote:  
> > >>>> From: Eugen Hristev <eugen.hristev@microchip.com>
> > >>>>
> > >>>> This allows the RTC node to have child nodes in DT.
> > >>>> This allows subnodes to be probed.
> > >>>>
> > >>>> Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
> > >>>> ---
> > >>>>    drivers/rtc/rtc-at91rm9200.c | 2 +-
> > >>>>    1 file changed, 1 insertion(+), 1 deletion(-)
> > >>>>
> > >>>> diff --git a/drivers/rtc/rtc-at91rm9200.c b/drivers/rtc/rtc-at91rm9200.c
> > >>>> index 3b833e0..f1b5b3d 100644
> > >>>> --- a/drivers/rtc/rtc-at91rm9200.c
> > >>>> +++ b/drivers/rtc/rtc-at91rm9200.c
> > >>>> @@ -421,7 +421,7 @@ static int __init at91_rtc_probe(struct platform_device *pdev)
> > >>>>         at91_rtc_write_ier(AT91_RTC_SECEV);
> > >>>>
> > >>>>         dev_info(&pdev->dev, "AT91 Real Time Clock driver.\n");
> > >>>> -     return 0;
> > >>>> +     return of_platform_populate(pdev->dev.of_node, NULL, NULL, &pdev->dev);
> > >>>>  
> > >>>
> > >>> You can avoid the DT binding change and DT parsing by using
> > >>> platform_add_device here. I don't think there is any point describing
> > >>> the trigger as a child node (a watchdog functionality wouldn't be
> > >>> described for example).
> > >>>  
> > >>
> > >> Hi,
> > >>
> > >> It's needed because the ADC needs a link to the trigger device. This is
> > >> a hardware link inside the SoC, so I thought the best way is to describe
> > >> this hardware is in the Device Tree.
> > >> Otherwise the ADC node is unaware of the RTC triggering possibility.
> > >> If we just assign the RTC trigger device to the ADC through the sysfs,
> > >> the ADC cannot distinguish between the RTC trigger and other various
> > >> triggers which can be attached.
> > >>  
> > > 
> > > I'm not sure this links is required but I will let Jonathan review. Even
> > > if it is needed, you can still use the rtc node to describe that link.  
> > 
> > Actually, the RTC node could potentially have two different ADC 
> > triggers. There is another OUT1 field that can do a second trigger for 
> > the ADC only for the last channel. Future development might add this 
> > trigger, so, with that in mind, I think it's best to link the exact 
> > trigger and not the RTC node.  
> 
> Nothing prevents you from using an index with the phandle (and I would
> add a type in that case then). Having subnodes in the DT is not really a
> good idea. The IP is the RTC, it just happens to have some outputs.
> See what has been done for the PMC.
> 
> 

If it can be done either way, let's avoid adding to the rtc dt binding.

Jonathan