linux-kernel - Re: [PATCH 04/10] rtc: at91rm9200: use of_platform

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Date:   Thu, 19 Dec 2019 11:23:21 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Eugen.Hristev@...rochip.com
Cc:     jic23@...nel.org, robh+dt@...nel.org, Nicolas.Ferre@...rochip.com,
        linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-rtc@...r.kernel.org, a.zummo@...ertech.it,
        Ludovic.Desroches@...rochip.com
Subject: Re: [PATCH 04/10] rtc: at91rm9200: use of_platform_populate as
 return value

On 19/12/2019 09:15:02+0000, Eugen.Hristev@...rochip.com wrote:
> 
> 
> On 18.12.2019 18:58, Alexandre Belloni wrote:
> > On 18/12/2019 16:52:21+0000, Eugen.Hristev@...rochip.com wrote:
> >>
> >>
> >> On 18.12.2019 18:43, Alexandre Belloni wrote:
> >>
> >>> Hi,
> >>>
> >>> On 18/12/2019 16:24:00+0000, Eugen.Hristev@...rochip.com wrote:
> >>>> From: Eugen Hristev <eugen.hristev@...rochip.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@...rochip.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.


-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com