linux-kernel - Re: [PATCH 4/4] usb: phy: omap-usb2: enable 960Mhz clock for omap5

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Message-ID: <5059DBA4.5010906@pengutronix.de>
Date:	Wed, 19 Sep 2012 16:50:12 +0200
From:	Marc Kleine-Budde <mkl@...gutronix.de>
To:	balbi@...com
CC:	Kishon Vijay Abraham I <kishon@...com>, grant.likely@...retlab.ca,
	rob.herring@...xeda.com, rob@...dley.net, linux@....linux.org.uk,
	linux-usb@...r.kernel.org, linux-omap@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 4/4] usb: phy: omap-usb2: enable 960Mhz clock for omap5

On 09/19/2012 04:42 PM, Felipe Balbi wrote:
> On Wed, Sep 19, 2012 at 04:45:01PM +0200, Marc Kleine-Budde wrote:
>> On 09/19/2012 01:56 PM, Felipe Balbi wrote:
>>> On Wed, Sep 19, 2012 at 05:00:29PM +0530, Kishon Vijay Abraham I wrote:
>>>> "usb_otg_ss_refclk960m" is needed by usb2 phy present in omap5. For
>>>> omap4, the clk_get of this clock will fail since it does not have this
>>>> clock.
>>>>
>>>> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
>>>> ---
>>>>  Documentation/devicetree/bindings/usb/usb-phy.txt |    3 +++
>>>>  drivers/usb/phy/omap-usb2.c                       |   28 ++++++++++++++++++++-
>>>>  2 files changed, 30 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/usb/usb-phy.txt b/Documentation/devicetree/bindings/usb/usb-phy.txt
>>>> index 7c5fd89..d5626de 100644
>>>> --- a/Documentation/devicetree/bindings/usb/usb-phy.txt
>>>> +++ b/Documentation/devicetree/bindings/usb/usb-phy.txt
>>>> @@ -24,6 +24,9 @@ Required properties:
>>>>  add the address of control module phy power register until a driver for
>>>>  control module is added
>>>>  
>>>> +Optional properties:
>>>> + - has960mhzclk: should be added if the phy needs 960mhz clock
>>>> +
>>>>  This is usually a subnode of ocp2scp to which it is connected.
>>>>  
>>>>  usb3phy@...84400 {
>>>> diff --git a/drivers/usb/phy/omap-usb2.c b/drivers/usb/phy/omap-usb2.c
>>>> index d36c282..d6612ba 100644
>>>> --- a/drivers/usb/phy/omap-usb2.c
>>>> +++ b/drivers/usb/phy/omap-usb2.c
>>>> @@ -146,6 +146,7 @@ static int __devinit omap_usb2_probe(struct platform_device *pdev)
>>>>  	struct omap_usb			*phy;
>>>>  	struct usb_otg			*otg;
>>>>  	struct resource			*res;
>>>> +	struct device_node		*np = pdev->dev.of_node;
>>>>  
>>>>  	phy = devm_kzalloc(&pdev->dev, sizeof(*phy), GFP_KERNEL);
>>>>  	if (!phy) {
>>>> @@ -190,6 +191,15 @@ static int __devinit omap_usb2_probe(struct platform_device *pdev)
>>>>  	}
>>>>  	clk_prepare(phy->wkupclk);
>>>>  
>>>> +	if (of_property_read_bool(np, "has960mhzclk")) {
>>>> +		phy->optclk = devm_clk_get(phy->dev, "usb_otg_ss_refclk960m");
>>>> +		if (IS_ERR(phy->optclk)) {
>>>> +			dev_err(&pdev->dev, "unable to get refclk960m\n");
>>>> +			return PTR_ERR(phy->optclk);
>>>> +		}
>>>> +		clk_prepare(phy->optclk);
>>>> +	}
>>>
>>> instead, can't you just always try to get the clock but ignore the error
>>> if it fails ?
>>
>> On imx we add no-op dummy clocks, so that the drivers will always find
>> all needed clocks. If a clk_get fails it's an error.
> 
> It's an error from a clk API point of view, it doesn't mean device can't
> work without that optional clock. Drivers are free to treat errors
> however they like, even by ignoring it and defaulting to some other
> behavior.

Sure.

> Adding dummy clocks just bloats the kernel with useless data IMHO.

Just wanted to point out there's more than one way to do it.

Marc
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