Re: [PATCH 2/5] dt-bindings: rtc: Add optional property "prescaler" in APM X-Gene RTC Document

From: Alexandre Belloni <alexandre.belloni@bootlin.com>
To: wefu@redhat.com
Cc: jszhang@kernel.org, robh@kernel.org,
	krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
	guoren@kernel.org, paul.walmsley@sifive.com, palmer@dabbelt.com,
	aou@eecs.berkeley.edu, linux-riscv@lists.infradead.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-rtc@vger.kernel.org
Subject: Re: [PATCH 2/5] dt-bindings: rtc: Add optional property "prescaler" in APM X-Gene RTC Document
Date: Fri, 12 Apr 2024 10:20:00 +0200	[thread overview]
Message-ID: <20240412082000279430d0@mail.local> (raw)
In-Reply-To: <20240412080238.134191-3-wefu@redhat.com>

On 12/04/2024 16:01:44+0800, wefu@redhat.com wrote:
> From: Wei Fu <wefu@redhat.com>
> 
> Add optional property "prescaler" for APM X-Gene RTC.
> The clock source on some platform to RTC is NOT 1HZ,
> so we need to prescale the clock to make the input clock become 1HZ,
> like (32K/prescaler) = 1HZ on the XuanTie TH1520 AP sub-system RTC.
> 
> Signed-off-by: Wei Fu <wefu@redhat.com>
> ---
>  .../devicetree/bindings/rtc/xgene-rtc.txt        | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/rtc/xgene-rtc.txt b/Documentation/devicetree/bindings/rtc/xgene-rtc.txt
> index fd195c358446..25ba8cf0cc31 100644
> --- a/Documentation/devicetree/bindings/rtc/xgene-rtc.txt
> +++ b/Documentation/devicetree/bindings/rtc/xgene-rtc.txt
> @@ -10,6 +10,9 @@ Required properties:
>  - #clock-cells: Should be 1.
>  - clocks: Reference to the clock entry.
>  
> +Optional properties:
> +- prescaler: Reference to the Value of Counter Prescaler.

What about getting the input clock rate and calculate the needed
prescaler instead of having it in the device tree?

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