linux-kernel - Re: [PATCH v1 1/5] dt-binding: rtci-pcf8523: add quartz

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Message-ID: <20180913190516.GG14988@piout.net>
Date:   Thu, 13 Sep 2018 21:05:16 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Andrew Jeffery <andrew@...id.au>,
        Fabio Estevam <fabio.estevam@....com>,
        Joel Stanley <joel@....id.au>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-rtc@...r.kernel.org,
        Søren Andersen <san@...v.dk>
Subject: Re: [PATCH v1 1/5] dt-binding: rtci-pcf8523: add quartz_load property

Hi,

You can remove 'rtci-' from the subject.

On 07/09/2018 21:35:04+0200, Sam Ravnborg wrote:
> From: Søren Andersen <san@...v.dk>
> 
> The NXP pcf8523 supports two different quartz loads.
> - 7 pF (default)
> - 12.5 pF (minimum power consumption)
> 
> The pcf8523 needs to know the size of the quartz load,
> otherwise the the RTC will have a bad precision.
> 
> The default for the rtc (after power-on) is 7 pF.
> Add a property that tells if the external capacitor is 12.5 pF.
> 
> Signed-off-by: Søren Andersen <san@...v.dk>
> Signed-off-by: Sam Ravnborg <sam@...nborg.org>
> Cc: Alessandro Zummo <a.zummo@...ertech.it>
> Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> ---
>  Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt | 19 +++++++++++++++++++
>  Documentation/devicetree/bindings/trivial-devices.txt |  1 -
>  2 files changed, 19 insertions(+), 1 deletion(-)
>  create mode 100644 Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt
> 
> diff --git a/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt b/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt
> new file mode 100644
> index 000000000000..7c5e93f5077c
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt
> @@ -0,0 +1,19 @@
> +* NXP PCF8523 Real Time Clock
> +
> +NXP PCF8523 Real Time Clock
> +
> +Required properties:
> +- compatible: Should contain "nxp,pcf8523".
> +- reg: I2C address for chip.
> +
> +Optional property:
> +- nxp,quartz_load_12.5pF: The capacitive load on the quartz is 12.5 pF,
> +  which differ from the default value of 7 pF
> +

The boolean properties usually don't work well for RTCs because people
usually want to keep any previous configuration that may have been done
at the factory or in the bootloader so I would use:

nxp,quartz_load_fF and this would be either 7000 or 12500.


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