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

[Matthias Brugger]

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@xxxxxxxxxxxx>
> > > ---
> > >  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.

Regards,
Matthias

> > Regards,
> > Matthias