linux-kernel - Re: [PATCH v2 2/3] ARM: DRA7x: dts: Update the OSC_32K

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Date:	Tue, 3 May 2016 11:16:38 +0300
From:	Tero Kristo <t-kristo@...com>
To:	"J.D. Schroeder" <Linux.HWI@...min.com>,
	<linux-kernel@...r.kernel.org>, <bcousson@...libre.com>,
	<tony@...mide.com>, <robh+dt@...nel.org>, <pawel.moll@....com>,
	<mark.rutland@....com>, <ijc+devicetree@...lion.org.uk>,
	<galak@...eaurora.org>, <linux@....linux.org.uk>,
	<linux-omap@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
CC:	<jay.schroeder@...min.com>
Subject: Re: [PATCH v2 2/3] ARM: DRA7x: dts: Update the OSC_32K_CLK frequency

On 02/05/16 20:12, J.D. Schroeder wrote:
> From: "J.D. Schroeder" <jay.schroeder@...min.com>
>
> This commit updates the OSC_32K_CLK (secure_32k_clk_src_ck) frequency
> from the precise 32kHz frequency (i.e., 32.768 kHz) to a more
> accurate frequency of ~34.6 kHz. Actual measured frequencies of the
> clock vary from processor to processor anywhere from 34.4 kHz up to
> 34.8 kHz. Note that the ~34 kHz frequency clock is generated
> internally by the processor, not an input to the processor. This
> change makes it more clear that the consumer of the
> secure_32k_clk_src_ck will not get a precise 32.768 kHz frequency
> output.
>
> Signed-off-by: J.D. Schroeder <jay.schroeder@...min.com>
> Reviewed-by: Trenton Andres <trenton.andres@...min.com>
> ---
>   arch/arm/boot/dts/dra7xx-clocks.dtsi | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm/boot/dts/dra7xx-clocks.dtsi b/arch/arm/boot/dts/dra7xx-clocks.dtsi
> index 3f0c61d..f7ec976 100644
> --- a/arch/arm/boot/dts/dra7xx-clocks.dtsi
> +++ b/arch/arm/boot/dts/dra7xx-clocks.dtsi
> @@ -95,7 +95,7 @@
>   	secure_32k_clk_src_ck: secure_32k_clk_src_ck {
>   		#clock-cells = <0>;
>   		compatible = "fixed-clock";
> -		clock-frequency = <32768>;
> +		clock-frequency = <34600>; /* approximate frequency */
>   	};
>
>   	sys_clk32_crystal_ck: sys_clk32_crystal_ck {
>

I still don't agree with this patch. The actual frequency can drift much 
more, you are just seeing this number at your setup. There is some 
internal discussion going on in TI about this, but I can't share any 
data on this yet.

-Tero