[PATCH v2 3/4] usb: chipidea: ci13xxx-imx: add "dr_mode" property to device tree bindings

[swarren@wwwdotorg.org (Stephen Warren)]

On 06/29/2012 02:45 AM, Richard Zhao wrote:
> On Fri, Jun 29, 2012 at 09:47:03AM +0200, Marc Kleine-Budde wrote:
>>
>> Cc'ed Devicetree Discussions
>>
>> On 06/29/2012 03:43 AM, Richard Zhao wrote:
>>> On Thu, Jun 28, 2012 at 03:53:48PM +0200, Marc Kleine-Budde wrote:
>>>> This patch allows the device tree to limit the chipidea to host or
>>>> peripheral mode only.
>>>>
>>>> Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
>>>> ---
>>>>  .../devicetree/bindings/usb/ci13xxx-imx.txt        |    3 ++
>>>>  drivers/usb/chipidea/ci13xxx_imx.c                 |    3 ++
>>>>  drivers/usb/chipidea/core.c                        |   41 +++++++++++++++++---
>>>>  include/linux/usb/chipidea.h                       |    9 +++++
>>>>  4 files changed, 50 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/usb/ci13xxx-imx.txt b/Documentation/devicetree/bindings/usb/ci13xxx-imx.txt
>>>> index 5a0ad66..67f97f56 100644
>>>> --- a/Documentation/devicetree/bindings/usb/ci13xxx-imx.txt
>>>> +++ b/Documentation/devicetree/bindings/usb/ci13xxx-imx.txt
>>>> @@ -4,6 +4,8 @@ Required properties:
>>>>  - compatible: Should be "fsl,imx27-usb"
>>>>  - reg: Should contain registers location and length
>>>>  - interrupts: Should contain controller interrupt
>>>> +- dr_mode: indicates the working mode for compatible controllers. Can
>>>> +  be "host", "peripheral", or "otg". Defaults to "otg" if not defined.
>>
>>> By default, it should be decided by capability registers. Only bad hw
>>> design needs such settings. So, why not name it as force-xxx? If it's
>>> not specific to imx, it doesn't needs to has prefix "fsl,".
>>
>> It's not a bad hardware design if you don't route or enable all ports a
>> soc offers. In modern socs you cannot enable all ports anyway.
>
> I'm not sure about your case, but generally, it's not about ports.
> It's about ID pin. If ID pin is not connect correctly, we may need to
> force it to host or device working mode. The 'force" here means it
> won't follow the capability registers and ID pin.
>>
>> The property isn't prefixed with "fsl,", it's just "dr_mode".
>>
>> Why not "force-xxx"? I had a look at Documentation/devicetree/bindings/usb:
>>
>> tegra-usb.txt:
>>>   - dr_mode : dual role mode. Indicates the working mode for
>>>    nvidia,tegra20-ehci compatible controllers.  Can be "host", "peripheral",
>>>    or "otg".  Default to "host" if not defined for backward compatibility.
>>>       host means this is a host controller
>>>       peripheral means it is device controller
>>>       otg means it can operate as either ("on the go")
>>
>> fsl-usb.txt:
>>>  - dr_mode : indicates the working mode for "fsl-usb2-dr" compatible
>>>    controllers.  Can be "host", "peripheral", or "otg".  Default to
>>>    "host" if not defined for backward compatibility.
>>>
>>
>> So why invent something new, if there seems to be a pattern?
>
> I'm not sure they mean the same things, because the default value is
> different. Event if they're same, why not make them all with sensible
> name?

I'm not quite sure what the question is I'm being asked here.

I certainly think that new bindings should follow existing precedent
where possible for representing the same data. dr_mode is that precedent
for a USB host's operating mode. Tegra chose to use that because of
precedent in fsl-usb.txt IIRC.