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Date:   Thu, 26 Apr 2018 21:58:03 -0500
From:   Rob Herring <robh@kernel.org>
To:     Amelie Delaunay <amelie.delaunay@st.com>
Cc:     Alessandro Zummo <a.zummo@towertech.it>,
        Alexandre Belloni <alexandre.belloni@free-electrons.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Alexandre Torgue <alexandre.torgue@st.com>,
        linux-rtc@vger.kernel.org, devicetree@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/4] dt-bindings: rtc: update stm32-rtc documentation for
 st,syscfg property
Message-ID: <20180427025803.mn32y5xle2p6knn6@rob-hp-laptop>
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On Thu, Apr 19, 2018 at 03:21:42PM +0200, Amelie Delaunay wrote:
> RTC driver should not be aware of the PWR registers offset and bits
> position. Furthermore, we can imagine that Disable Backup Protection (DBP)
> relative register and bit mask could change depending on the SoC. So this
> patch moves st,syscfg property from single pwrcfg phandle to pwrcfg
> phandle/offset/mask triplet.
> 
> Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
> ---
>  Documentation/devicetree/bindings/rtc/st,stm32-rtc.txt | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/rtc/st,stm32-rtc.txt b/Documentation/devicetree/bindings/rtc/st,stm32-rtc.txt
> index a66692a..00f8b5d 100644
> --- a/Documentation/devicetree/bindings/rtc/st,stm32-rtc.txt
> +++ b/Documentation/devicetree/bindings/rtc/st,stm32-rtc.txt
> @@ -14,8 +14,10 @@ Required properties:
>      It is required only on stm32h7.
>  - interrupt-parent: phandle for the interrupt controller.
>  - interrupts: rtc alarm interrupt.
> -- st,syscfg: phandle for pwrcfg, mandatory to disable/enable backup domain
> -  (RTC registers) write protection.
> +- st,syscfg: phandle/offset/mask triplet. The phandle to pwrcfg used to
> +  access control register at offset, and change the dbp (Disable Backup
> +  Protection) bit represented by the mask, mandatory to disable/enable backup
> +  domain (RTC registers) write protection.

It's fine to add this, but you are breaking compatibility in the driver 
with existing DTBs by requiring these new fields.

Rob