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

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Date:   Wed, 25 Jan 2017 00:23:23 +0100
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     Chunfeng Yun <chunfeng.yun@...iatek.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 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.

Regards,
Matthias

>>
>> Regards,
>> Matthias
>
>