linux-kernel - Re: [PATCH v2 1/4] ARM: dts: omap4-panda: Add USB Host support

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Message-ID: <51C19E6C.4040802@epfl.ch>
Date:	Wed, 19 Jun 2013 14:05:00 +0200
From:	Florian Vaussard <florian.vaussard@...l.ch>
To:	Roger Quadros <rogerq@...com>
CC:	Benoit Cousson <b-cousson@...com>,
	devicetree-discuss@...ts.ozlabs.org, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/4] ARM: dts: omap4-panda: Add USB Host support

Hello,

On 06/19/2013 01:03 PM, Roger Quadros wrote:
> On 06/19/2013 01:10 PM, Benoit Cousson wrote:
>> On 06/19/2013 02:46 AM, Tony Lindgren wrote:
>>> * Roger Quadros <rogerq@...com> [130619 00:42]:
>>>> Hi Benoit,
>>>>
>>>> On 06/19/2013 04:17 AM, Benoit Cousson wrote:
>>>>> Hi Roger,
>>>>>
>>>>> On 06/18/2013 11:04 AM, Roger Quadros wrote:
>>>>>> Provide the RESET and Power regulators for the USB PHY,
>>>>>> the USB Host port mode and the PHY device.
>>>>>>
>>>>>> Also provide pin multiplexer information for the USB host
>>>>>> pins.
>>>>>>
>>>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>>>> ---
>>>>>>     arch/arm/boot/dts/omap4-panda-common.dtsi |   62 +++++++++++++++++++++++++++++
>>>>>>     1 files changed, 62 insertions(+), 0 deletions(-)
>>>>>>
>>>>>> diff --git a/arch/arm/boot/dts/omap4-panda-common.dtsi b/arch/arm/boot/dts/omap4-panda-common.dtsi
>>>>>> index 00cbaa5..7a21e8e 100644
>>>>>> --- a/arch/arm/boot/dts/omap4-panda-common.dtsi
>>>>>> +++ b/arch/arm/boot/dts/omap4-panda-common.dtsi
>>>>>> @@ -59,6 +59,42 @@
>>>>>>                 "AFML", "Line In",
>>>>>>                 "AFMR", "Line In";
>>>>>>         };
>>>>>> +
>>>>>> +    /* HS USB Port 1 RESET */
>>>>>> +    hsusb1_reset: hsusb1_reset_reg {
>>>>>> +        compatible = "regulator-fixed";
>>>>>> +        regulator-name = "hsusb1_reset";
>>>>>> +        regulator-min-microvolt = <3300000>;
>>>>>> +        regulator-max-microvolt = <3300000>;
>>>>>> +        gpio = <&gpio2 30 0>;    /* gpio_62 */
>>>>>> +        startup-delay-us = <70000>;
>>>>>> +        enable-active-high;
>>>>>> +    };
>>>>>
>>>>> Is this really a regulator? Or just a GPIO line used to reset the USB PHY?
>>>>
>>>> It is in fact a GPIO line used as reset.
>>>>>
>>>>> If this is the case, I don't think it should be represented as a regulator.
>>>>
>>>> Why not? I think it fits very well in the regulator device model.
>>
>> I'm not sure fitting very well is the correct term.
>> It works, for sure, but it is no different than when we were trying to abuse the regulator fmwk to enable the 32k clock in phoenix.
>> It is just a hack.
>>
>
> The only difference is there is a dedicated framework for clocks. Since there is nothing specific to
> handle reset lines it is left to the driver writer how he wants to manage it.
>

There is a proposed binding for gpio-controlled reset lines, but it is 
not yet merged [1].
I guess it can fit most usage patterns, and it can be an interesting 
move in the future.

Regards,

Florian

[1] http://thread.gmane.org/gmane.linux.drivers.devicetree/36830
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