Re: [PATCH 1/7] usb: dwc3: get "usb_phy" only if the platform indicates the presence of PHY

From: Roger Quadros <rogerq@ti.com>
To: Vivek Gautam <gautamvivek1987@gmail.com>
Cc: Kishon Vijay Abraham I <kishon@ti.com>,
	Felipe Balbi <balbi@ti.com>,
	Benoit Cousson <bcousson@baylibre.com>,
	Tony Lindgren <tony@atomide.com>,
	Rob Herring <rob.herring@calxeda.com>,
	Pawel Moll <pawel.moll@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Russell King - ARM Linux <linux@arm.linux.org.uk>,
	Grant Likely <grant.likely@linaro.org>,
	Sylwester Nawrocki <s.nawrocki@samsung.com>,
	Kumar Gala <galak@codeaurora.org>,
	Stephen Warren <swarren@wwwdotorg.org>,
	Ian Campbell <ian.campbell@citrix.com>,
	Rob Landley <rob@landley.net>, <george.cherian@ti.com>,
	Greg KH <gregkh@linuxfoundation.org>, <linux-doc@vger.kernel.org>,
	<linux-omap@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	Linux USB Mailing List <linux-usb@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/7] usb: dwc3: get "usb_phy" only if the platform indicates the presence of PHY
Date: Thu, 12 Sep 2013 16:11:59 +0300	[thread overview]
Message-ID: <5231BD9F.4020105@ti.com> (raw)
In-Reply-To: <CAFp+6iGzV4auP0AeySen2Qk6wEJM-xsTnQmfwMQDtp2tg1FMkQ@mail.gmail.com>

On 09/12/2013 02:26 PM, Vivek Gautam wrote:
> Hi,
> 
> 
> On Thu, Sep 12, 2013 at 4:34 PM, Roger Quadros <rogerq@ti.com> wrote:
>> Hi,
>>
>> On 09/12/2013 01:47 PM, Vivek Gautam wrote:
>>> On Thu, Sep 12, 2013 at 4:06 PM, Roger Quadros <rogerq@ti.com> wrote:
>>>> Hi Kishon,
>>>>
>>>> On 09/02/2013 06:43 PM, Kishon Vijay Abraham I wrote:
>>>>> There can be systems which does not have a external usb_phy, so get
>>>>> usb_phy only if usb-phy property is added in the case of dt boot or if
>>>>> platform_data indicates the presence of PHY. Also remove checking if
>>>>> return value is -ENXIO since it's now changed to always enable usb_phy layer.
>>>>>
>>>>> Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
>>>>> ---
>>>>>  drivers/usb/dwc3/Kconfig         |    1 +
>>>>>  drivers/usb/dwc3/core.c          |   60 +++++++++++++++++---------------------
>>>>>  drivers/usb/dwc3/platform_data.h |    1 +
>>>>>  3 files changed, 28 insertions(+), 34 deletions(-)
>>>>>
>>>>> diff --git a/drivers/usb/dwc3/Kconfig b/drivers/usb/dwc3/Kconfig
>>>>> index f969ea2..cfc16dd 100644
>>>>> --- a/drivers/usb/dwc3/Kconfig
>>>>> +++ b/drivers/usb/dwc3/Kconfig
>>>>> @@ -2,6 +2,7 @@ config USB_DWC3
>>>>>       tristate "DesignWare USB3 DRD Core Support"
>>>>>       depends on (USB || USB_GADGET) && GENERIC_HARDIRQS && HAS_DMA
>>>>>       depends on EXTCON
>>>>> +     select USB_PHY
>>>>>       select USB_XHCI_PLATFORM if USB_SUPPORT && USB_XHCI_HCD
>>>>>       help
>>>>>         Say Y or M here if your system has a Dual Role SuperSpeed
>>>>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>>>>> index 474162e..428c29e 100644
>>>>> --- a/drivers/usb/dwc3/core.c
>>>>> +++ b/drivers/usb/dwc3/core.c
>>>>> @@ -387,16 +387,38 @@ static int dwc3_probe(struct platform_device *pdev)
>>>>>       if (node) {
>>>>>               dwc->maximum_speed = of_usb_get_maximum_speed(node);
>>>>>
>>>>> -             dwc->usb2_phy = devm_usb_get_phy_by_phandle(dev, "usb-phy", 0);
>>>>> -             dwc->usb3_phy = devm_usb_get_phy_by_phandle(dev, "usb-phy", 1);
>>>>> +             if (of_property_read_bool(node, "usb-phy")) {
>>>>> +                     dwc->usb2_phy = devm_usb_get_phy_by_phandle(dev,
>>>>> +                             "usb-phy", 0);
>>>>> +                     if (IS_ERR(dwc->usb2_phy))
>>>>> +                             return PTR_ERR(dwc->usb2_phy);
>>>>> +                     dwc->usb3_phy = devm_usb_get_phy_by_phandle(dev,
>>>>> +                             "usb-phy", 1);
>>>>> +                     if (IS_ERR(dwc->usb3_phy))
>>>>> +                             return PTR_ERR(dwc->usb3_phy);
>>>>
>>>> Some DWC3 instances use only usb2_phy. e.g. on DRA7 the 2nd dwc3 instance doesn't use usb3_phy.
>>>> This needs to be a valid case and driver shouldn't error out.
>>>
>>> So, i think adding flexibility to DWC3 to have either
>>> usb2-phy/usb3-phy or both of them seems to be valid point.
>>> Any suggestions ?
>>>
>>
>> For high speed operation we need only usb2_phy but for super speed we need both usb2_phy
>> and usb3_phy.
>>
>> Why would a dwc3 controller use only usb3_phy? A USB3.0 interface has to be compatible with
>> USB2.0 as well, no?
> 
> True and for that reason we need both UTMI+ interface as well as PIPE3
> interface, right ?
> But as also mentioned in the thread:
> https://lkml.org/lkml/2013/9/12/181, on Samsung exynos5
> architecturally same block is managing UTMI+ and PIPE3 interfaces,
> which is handled by phy-samsung-usb3 driver and denoted by "usb3_phy:
> usbphy@12100000" node in "arch/arm/boot/dts/exynos5250.dtsi".
> 
> So on exynos5250, DWC3 really needs just usb3-phy, which is compatible
> for USB 2.0 as well.

I'm not familiar with exynos5250 dwc3, but looking at the dts file I can see both usb3_phy
and usb2_phy nodes and both are referenced in the dwc3 node.

The ehci and ohci controllers don't reference any PHY.

cheers,
-roger