linux-kernel - RE: [PATCH 1/2] Documentation: can: flexcan: add PE clock source property to device tree

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Message-ID: <DB7PR04MB46185ACEDA227BEFCED6971DE6B80@DB7PR04MB4618.eurprd04.prod.outlook.com>
Date:   Fri, 21 Dec 2018 04:28:16 +0000
From:   Joakim Zhang <qiangqing.zhang@....com>
To:     Rob Herring <robh@...nel.org>
CC:     "mkl@...gutronix.de" <mkl@...gutronix.de>,
        "linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        Aisheng Dong <aisheng.dong@....com>
Subject: RE: [PATCH 1/2] Documentation: can: flexcan: add PE clock source
 property to device tree


> -----Original Message-----
> From: Rob Herring <robh@...nel.org>
> Sent: 2018年12月21日 4:23
> To: Joakim Zhang <qiangqing.zhang@....com>
> Cc: mkl@...gutronix.de; linux-can@...r.kernel.org;
> devicetree@...r.kernel.org; linux-kernel@...r.kernel.org; dl-linux-imx
> <linux-imx@....com>; Aisheng Dong <aisheng.dong@....com>
> Subject: Re: [PATCH 1/2] Documentation: can: flexcan: add PE clock source
> property to device tree
> 
> On Thu, Dec 13, 2018 at 07:07:57AM +0000, Joakim Zhang wrote:
> > From: Dong Aisheng <aisheng.dong@....com>
> >
> > The FlexCAN controller can parse clock source property from DTS file
> > to select PE clock source.
> >
> > Signed-off-by: Dong Aisheng <aisheng.dong@....com>
> > Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
> > ---
> >  Documentation/devicetree/bindings/net/can/fsl-flexcan.txt | 8
> > ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/net/can/fsl-flexcan.txt
> > b/Documentation/devicetree/bindings/net/can/fsl-flexcan.txt
> > index bc77477c6878..a04168605998 100644
> > --- a/Documentation/devicetree/bindings/net/can/fsl-flexcan.txt
> > +++ b/Documentation/devicetree/bindings/net/can/fsl-flexcan.txt
> > @@ -32,6 +32,13 @@ Optional properties:
> >  		 ack_gpr is the gpr register offset of CAN stop acknowledge.
> >  		 ack_bit is the bit offset of CAN stop acknowledge.
> >
> > +- fsl,clk-source: Select the clock source to the CAN Protocol Engine (PE).
> > +		  It's SoC Implementation dependent. Refer to RM for detailed
> 
> If SoC dependent, then it should be implied by the SoC specific compatible.
> Also, seems like you should add clock binding support here if you need more
> clock control.

Hi,

My expression here might not be very accurate, this property just help to select the clock source for
Protocol Engine (PE). FlexCAN ip support two PE clock sources, so we have to add this property to
let driver know that SoC has selected which one.

Best Regards,
Joakim Zhang

> > +		  definition. If this property is not set in device tree node
> > +		  then driver selects clock source 1 by default.
> > +		  0: clock source 0 (oscillator clock)
> > +		  1: clock source 1 (peripheral clock)
> > +
> >  Example:
> >
> >  	can@...00 {
> > @@ -40,4 +47,5 @@ Example:
> >  		interrupts = <48 0x2>;
> >  		interrupt-parent = <&mpic>;
> >  		clock-frequency = <200000000>; // filled in by bootloader
> > +		fsl,clk-source = <0>; // select clock source 0 for PE
> >  	};
> > --
> > 2.17.1
> >