linux-kernel - Re: [PATCH] USB: ehci-omap: Select USB

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Message-ID: <5166CE56.2070400@ti.com>
Date:	Thu, 11 Apr 2013 17:53:10 +0300
From:	Roger Quadros <rogerq@...com>
To:	<balbi@...com>
CC:	Greg KH <gregkh@...uxfoundation.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Linux USB Mailing List <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: Re: [PATCH] USB: ehci-omap: Select USB_PHY

On 04/11/2013 05:34 PM, Felipe Balbi wrote:
> Hi,
> 
> On Thu, Apr 11, 2013 at 04:18:33PM +0300, Roger Quadros wrote:
>> On 04/11/2013 03:42 PM, Roger Quadros wrote:
>>> On 04/11/2013 01:55 PM, Felipe Balbi wrote:
>>>> Hi,
>>>>
>>>> On Thu, Apr 11, 2013 at 01:51:16PM +0300, Roger Quadros wrote:
>>>>> On 04/11/2013 01:04 PM, Felipe Balbi wrote:
>>>>>> Hi,
>>>>>>
>>>>>> On Thu, Apr 11, 2013 at 12:42:04PM +0300, Roger Quadros wrote:
>>>>>>> Hi Greg,
>>>>>>>
>>>>>>> The following patch gets rid of Kbuild warnings when USB_EHCI_HCD_OMAP
>>>>>>> is enabled.
>>>>>>>
>>>>>>> Patch is based on your usb-next branch and is needed for 3.10.
>>>>>>>
>>>>>>> From: Roger Quadros <rogerq@...com>
>>>>>>> Date: Thu, 11 Apr 2013 12:08:19 +0300
>>>>>>> Subject: [PATCH] USB: ehci-omap: Select USB_PHY
>>>>>>>
>>>>>>> As we need NOP_USB_XCEIV which depends on USB_PHY
>>>>>>> we need to select USB_PHY as well.
>>>>>>>
>>>>>>> Gets rid of the below warnings when USB_EHCI_HCD_OMAP
>>>>>>> is enabled.
>>>>>>>
>>>>>>> warning: (USB_EHCI_HCD_OMAP) selects NOP_USB_XCEIV which has unmet direct dependencies (USB_SUPPORT && USB_PHY)
>>>>>>> warning: (USB_EHCI_HCD_OMAP) selects NOP_USB_XCEIV which has unmet direct dependencies (USB_SUPPORT && USB_PHY)
>>>>>>>
>>>>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>>>>
>>>>>> Ideally, however, we wouldn't select any PHY in particular as different
>>>>>> boards might need a different PHY driver, even on OMAP ;-)
>>>>>>
>>>>> Right, but we need to select USB_PHY here as the driver uses
>>>>> the USB_PHY APIs.
>>>>>
>>>>> The NOP_USB_XCEIV selection could be done by the board config.
>>>>
>>>> I would avoid 'select' completely and just update omap2plus_defconfig
>>>> adding those two as modules.
>>>>
>>>
>>> OK, makes sense. I will update the patch to remove "select NOP_USB_XCEIV".
>>>
>>
>> One more issue to clarify.
>>
>> if USB_PHY is not enabled, then all phy_get() API's should return NULL and not
>> -ENXIO as it does now.
> 
> ENXIO means "No such device or address", looks alright to me ;-)
> 
>> This way the drivers need not treat it as an error and all PHY ops can
>> be NOPs.
> 
> drivers will already be using if (IS_ERR()) construction, returning
> -ENXIO when the API is disabled gives them an oportunity to *not*
> request probe deferral since the API isn't enabled anyway.

on second thoughts I agree with you. So the general understanding is
that USB_PHY users without USB_PHY enabled is an error case.

This means we need to allow controller drivers to select USB_PHY
and minimize this possibility.

> 
>> This will make it behave like other frameworks. e.g. clk.
> 
> if we return NULL we will need IS_ERR_OR_NULL() which will cause
> problems with people who aren't careful enough.
> 
OK.

cheers,
-roger
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