linux-kernel - Re: [PATCH 2/6] usb: mtu3: add reference clock

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Date:   Fri, 20 Jan 2017 10:20:25 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Matthias Brugger <matthias.bgg@...il.com>
CC:     Mathias Nyman <mathias.nyman@...el.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        "Mark Rutland" <mark.rutland@....com>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-usb@...r.kernel.org>, <linux-mediatek@...ts.infradead.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/6] usb: mtu3: add reference clock

On Thu, 2017-01-19 at 13:22 +0100, Matthias Brugger wrote:
> 
> On 18/01/17 07:08, Chunfeng Yun wrote:
> > usually, the reference clock comes from 26M oscillator directly,
> > but some SoCs are not, add it for compatibility.
> >
> > Signed-off-by: Chunfeng Yun <chunfeng.yun@...iatek.com>
> > ---
> >  drivers/usb/mtu3/mtu3.h      |    1 +
> >  drivers/usb/mtu3/mtu3_plat.c |   21 +++++++++++++++++++--
> >  2 files changed, 20 insertions(+), 2 deletions(-)
[...]
> > @@ -154,6 +162,7 @@ static int ssusb_rscs_init(struct ssusb_mtk *ssusb)
> >  static void ssusb_rscs_exit(struct ssusb_mtk *ssusb)
> >  {
> >  	clk_disable_unprepare(ssusb->sys_clk);
> > +	clk_disable_unprepare(ssusb->ref_clk);
> >  	regulator_disable(ssusb->vusb33);
> >  	ssusb_phy_power_off(ssusb);
> >  	ssusb_phy_exit(ssusb);
> > @@ -216,6 +225,12 @@ static int get_ssusb_rscs(struct platform_device *pdev, struct ssusb_mtk *ssusb)
> >  		return PTR_ERR(ssusb->sys_clk);
> >  	}
> >
> > +	ssusb->ref_clk = devm_clk_get(dev, "ref_ck");
> > +	if (IS_ERR(ssusb->ref_clk)) {
> > +		dev_err(dev, "failed to get ref clock\n");
> > +		return PTR_ERR(ssusb->ref_clk);
> > +	}
> > +
> 
> That would break older dts bindings, right?
Yes, So I send a new patch for the related dts. Maybe it's not a
problem, only one dts file need be updated currently.

> ref_ck must be optional for the code.
I tend to make it be optional for the dts, but not for the code.
There are some "fixed-clock" which can be treated as dummy ones, and if
a clock is really optional, we can use one fixed-clock in dts, and keep
the code simple.
In fact, the reference clock is essential for usb controller.
> 
> Regards,
> Matthias