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

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Date:   Mon, 6 Feb 2017 15:03:41 +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 Wed, 2017-01-25 at 00:23 +0100, Matthias Brugger wrote:
> 
> On 01/20/2017 03:20 AM, Chunfeng Yun wrote:
> > 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.
> 
> Well the thing is that there are devices in the field with an older dtb 
> which would break on a newer kernel. That's why we need to make it work 
> with the old dtb in the code as well.
> 
Happy Chinese New Year!

Ok, I will make it optional.

Thanks and sorry for later reply.

> Regards,
> Matthias
> 
> >>
> >> Regards,
> >> Matthias
> >
> >