linux-kernel - Re: [PATCH v2 2/2] arm: dts: add support for AM437x StarterKit

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Message-ID: <53A2564E.2080600@ti.com>
Date:	Wed, 18 Jun 2014 22:17:34 -0500
From:	Nishanth Menon <nm@...com>
To:	<balbi@...com>
CC:	<devicetree@...r.kernel.org>, <linux@....linux.org.uk>,
	Benoit Cousson <bcousson@...libre.com>,
	Tony Lindgren <tony@...mide.com>,
	Rajendra Nayak <rnayak@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Darren Etheridge <detheridge@...com>, <r.sricharan@...com>,
	<robh+dt@...nel.org>, Josh Elliot <jelliott@...com>,
	<galak@...eaurora.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel Mailing List 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 2/2] arm: dts: add support for AM437x StarterKit

On 06/18/2014 10:05 PM, Felipe Balbi wrote:
> Hi,
> 
> On Wed, Jun 18, 2014 at 09:26:01PM -0500, Nishanth Menon wrote:
>> On 06/18/2014 06:19 PM, Felipe Balbi wrote:
>> [...]
>>>>>>> Add support for TI's AM437x StarterKit Evaluation
>>>>>>> Module.
>>>>>>
>>>>>> is there a link for this platform?
>>>>>
>>>>> internal only
>>>>
>>>> but will eventually be sold externally? I assume this is not an TI
>>>
>>> probably, but there's nothing public yet.
>>>
>>>> internal only board.
>>>
>>> correct assumption for all I know.
>>
>> Yikes.. ok.. I'd let Tony et.al make the call on this, I guess.
> 
> would we really block a DTS just because there's no public wiki page
> available (yet) ?
> 
> Sounds a bit extreme to me.

If this is an TI internal board without anyone outside that a few
select developers being able to get and work on it... I am a bit
skeptical on upstream kernel support and burden for forseeable future
in ensuring it is tested and continually maintained. if it an
one-off.. maybe fork might be good enough.. upstream not too attractive.

I mean, if it is targeted to be sold eventually, I have no objections
or blocks - just make it clear in commit message. I can imagine folks
wondering what the heck this is and googling without results(just like
I did).

[...]

>>>>>>> +	cd-gpios = <&gpio0 6 GPIO_ACTIVE_HIGH>;
>>>>>>> +};
>>>>>>> +
>>>>>>> +&usb2_phy1 {
>>>>>>> +	status = "okay";
>>>>>>> +};
>>>>>>> +
>>>>>>> +&usb1 {
>>>>>>> +	dr_mode = "peripheral";
>>>>>>> +	status = "okay";
>>>>>>> +};
>>>>>>> +
>>>>>>> +&usb2_phy2 {
>>>>>>> +	status = "okay";
>>>>>>> +};
>>>>>>> +
>>>>>>> +&usb2 {
>>>>>>> +	dr_mode = "host";
>>>>>>> +	status = "okay";
>>>>>>> +};
>>>>>> none of the above need pinctrl? no regulator supplies?
>>>>>
>>>>> pins in default states, drivers don't use regulators.
>>>>
>>>> USB works without a supply? even a fixed voltage supply? that is
>>>> weird.
>>>
>>> take a look at the minicom output I posted if you don't believe. Well,
>>> to be exact, tps63010 [1] is the one which generates the regulated V5_0D
>>> which is used as VBUS_USB. The enable pin in that device is tied to the
>>> 3v3 rail (dcdc4 regulator in the PMIC as most everything else) but
>>> there's no way (otherwise) to control that thing. There's no control
>>> bus, no way to write a driver.
>>>
>>> Since the board will anyways turn off if you disable the 3v3 rail, it's
>>> pretty much pointless to figure out a hack just to add this to DTS.
>>>
>>> [1] http://www.ti.com/product/TPS63010
>>
>> I am sure to trust you on the test log :) ->  but then from dts description
>> perspective, it is good if we describe the supplies, even as a always on
>> fixed-regulator. We had instances like 2430SDP ethernet where... umm... we
>> originally missed describing ethernet supply and boom, one fine morning, no
>> more nfs filesystem - I mean, it is a one off scenario there, but describing
>> regulators helps us atleast understand the power tree of the board a little
>> better.
>>
>> Again, no strong opinions on my side, it is a good thing to do is all
>> I feel about it.
> 
> you mean something like:
> 
> 	V5_0D: fixedregulator@0 {
> 		compatible = "regulator-fixed";
> 		regulator-name = "V5_0D";
> 		regulator-min-microvolt = <5000000>;
> 		regulator-max-microvolt = <5000000>;
> 		regulator-boot-on;
> 		regulator-always-on;
> 		vin-supply = <&dcdc4>;
> 	};
> 
> 	VBUS_USB: fixedregulator@1 {
> 		compatible = "regulator-fixed";
> 		regulator-name = "VBUS_USB";
> 		regulator-min-microvolt = <5000000>;
> 		regulator-max-microvolt = <5000000>;
> 		regulator-boot-on;
> 		regulator-always-on;
> 		vin-supply = <&V5_0D>;
> 	};
> 
> I can add that, but note that it's *solely* to make sysfs look nice. And
> if that's the case, most likely *every* DTS file in tree today as
> incomplete. OTOH, I really consider this to be hugely unnecessary
> because of the fact that board will turn off if 3v3 (dcdc4) is disabled.
> 


Yes - something along those lines - Again, no strong opinions on my
side for these - just that it is a good thing to model in and may help
drivers where can use the awareness.

Regards,
Nishanth Menon
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