linux-kernel - Re: [PATCH v2 1/4] devicetree: bindings: Properly document micrel ks8851 SPI chips

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Message-ID: <53863CA3.7040000@codeaurora.org>
Date:	Wed, 28 May 2014 12:44:35 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Mark Brown <broonie@...nel.org>
CC:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	"David S . Miller" <davem@...emloft.net>,
	Nishanth Menon <nm@...com>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	linux-arm-msm@...r.kernel.org, Kumar Gala <galak@...eaurora.org>,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	Rob Herring <robh+dt@...nel.org>, netdev@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/4] devicetree: bindings: Properly document micrel
 ks8851 SPI chips

On 05/28/14 10:12, Mark Brown wrote:
> On Wed, May 28, 2014 at 05:16:46PM +0200, Uwe Kleine-König wrote:
>> On Tue, May 27, 2014 at 02:40:15PM -0700, Stephen Boyd wrote:
>>> On 05/24/14 05:48, Mark Brown wrote:
>>>> So, according to the datasheet I managed to find this device has a
>>>> supply VDD_IO (so normally written vdd-io-supply here), some other
>>>> supplies which are tied to VDD_IO (so can probably be omitted) and a
>>>> supply VDD_A3.3 none of which are optional.  There is an internal
>>>> regulator which can be used to drop a higher voltage VDD_IO down for
>>>> some of the supplies tied to it but that's essentially a noop from
>>>> software as far as I can tell.  None of these supplies are obviously
>>>> optional, though I've not read the datasheet in detail so I may have
>>>> missed something here.
>> There is a difference between the supply being optional for the hardware
>> to work and the need to specify it in the device tree, isn't it? My
>> expectation is that when it's not specified there is just nothing the
>> the software needs to care for. 
> If the supply must always be physically present the bindings should be
> specified as it being mandatory and the code written in that fashion; as
> an extension Linux will put a dummy in but this is attempting to handle
> incorrect DTs.  This means we have functional error handling in cases
> where there is something to worry about and simplifies the code using
> the regulator.

Ok, you're saying the opposite of Rob. Should it be required or optional
in the DT binding?

>
> regulator_get_optional() should *only* be used if the supply may be
> omitted from the physical design and should generally always be
> accompanied by code which does something substantially different such as
> using an internal regulator or changing the source for a reference
> voltage instead.
>
>

Ok. Dave M has already picked up all these patches so I'll send a patch
to replace regulator_get_optional() with regulator_get() and fix up the
error handling unless I hear otherwise.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by The Linux Foundation

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