Message-ID: <54B3C2F4.4010007@free-electrons.com>
Date:	Mon, 12 Jan 2015 13:49:56 +0100
From:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
To:	Hans de Goede <hdegoede@...hat.com>,
	Mark Brown <broonie@...nel.org>
CC:	Chen-Yu Tsai <wens@...e.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Boris BREZILLON <boris.brezillon@...e-electrons.com>,
	Jason Cooper <jason@...edaemon.net>,
	Tawfik Bayouk <tawfik@...vell.com>,
	Andrew Lunn <andrew@...n.ch>,
	devicetree <devicetree@...r.kernel.org>,
	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>,
	Mark Rutland <mark.rutland@....com>,
	Nadav Haklai <nadavh@...vell.com>, linux-ide@...r.kernel.org,
	Lior Amsalem <alior@...vell.com>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Tejun Heo <tj@...nel.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v2 2/4] Documentation: bindings: Add the regulator property
 to the sub-nodes AHCI bindings

On 10/01/2015 14:51, Hans de Goede wrote:
> Hi,
> 
> On 10-01-15 12:17, Mark Brown wrote:
>> On Sat, Jan 10, 2015 at 11:20:13AM +0100, Hans de Goede wrote:
>>> On 09-01-15 18:11, Mark Brown wrote:
>>
>>>> Or if the supply is for the device at the other end of the link (which
>>>> is what it sounded like) then use that.  This just sounds like the same
>>>> problem we have for all the enumerable buses in embedded systems where
>>>> we need to be able to understand that the device exists prior to it
>>>> being fully ready to appear in the system.  Having the link/slot be a
>>>> device in Linux does indeed seem to be a common way people think about
>>>> doing this, it sounds like for this one it might be the most direct.
>>
>>> I think we should be careful to not think too much from an implementation
>>> pov here, the purpose of the devicetree description is to describe the hardware,
>>> as is.
>>
>> I don't think anyone is talking about changing the DT here, only the way
>> it's represented inside Linux.
>>
>>>                  sata0: sata-port@0 {
>>>                          reg = <0>;
>>>                          phys = <&sata_phy 0>;
>>> 			target-supply = <&reg_sata0>;
>>>                  };
>>>
>>>                  sata1: sata-port@1 {
>>>                          reg = <1>;
>>>                          phys = <&sata_phy 1>;
>>> 			target-supply = <&reg_sata1>;
>>>                  };
>>>          };
>>
>>> Seems to match the hardware pretty exactly, and also matches how we've
>>> been describing similar devices with only one sata port + power plug sofar,
>>> so from a consistency pov it also is a good model.
>>
>> Right, I think that makes sense
> 
> Good, as said I think getting the dt bit rights is the most important
> thing here. So if we agree that the above dt example looks sane, lets see
> how we can best implement that.
> 
>  > it also looks to me like these things
>> should be representable as devices within Linux.
> 
> I guess we could manually instantiate platform devices for each of the
> subnodes which represent an sata port here, yes that should not be
> hard to do, it feels like a bit overkill though.
> 
> So for our this should likely look something like this:
> 
>          if (IS_ENABLED(CONFIG_OF_ADDRESS) && dev->of_node) {
>                  for_each_child_of_node(dev->of_node, np) {
>                          pdev[i++] = of_platform_device_create(np, NULL, NULL);
>                  }
>          }
> 
> and then loop over the pdev[] array and get the regulator, and phy for each.
> 
> I wonder if of_platform_device_create can deal with nodes with
> #size-cells = <0>; is 0 though, if it cannot maybe we need to teach it.
> 
>>> So supporting this model requires having a regulator_get API which allows
>>> specifying which of_node to get the regulator from, e.g. the proposed
>>
>> It requires nothing of the sort.
> 
> You're proposed solution of instantiating devices does more or less exactly
> what I say is required, it is a way to pass an of_node into regulator_get,
> but you're hiding the node inside dev->of_node. I can see the appeal in
> that.
> 
>>> of_regulator_get function. I know you (Mark) do not like this, but all
>>> other subsystems have an of_foo_get function taking an of_node as argument,
>>> I do not see how the regulator subsys is so special that it cannot have one,
>>> and also notice that this is only a kernel internal API which we can always
>>> change later.
>>
>> Two things there.  One is that mostly those APIs are legacy APIs from
>> before we made DT a first class citizen and generally they shouldn't be
>> used these days.  The other is that at least for regulators we have
>> constant problems with people abusing the API in various ways, as a
>> result the API has a goal of not helping undesirable usage patterns in
>> order to help people spot problems.  Having an API which makes it easy
>> create broken bindings means that it is much more likely that people
>> will do just that.
> 
> Hmm I can see where you're coming from, and your proposed solution may
> also be useful for when we get similar boards requiring explicit regulator
> handling with the sata ports described in ACPI tables.
> 
> Gregory, can you give the setup using per sata port devices a try, and
> see how that works out code wise ?

OK, I am taking care of it.


Thanks,

Gregory

-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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