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

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Message-ID: <20140528151646.GU20155@pengutronix.de>
Date:	Wed, 28 May 2014 17:16:46 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Mark Brown <broonie@...nel.org>,
	"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

Hello Stephen,

On Tue, May 27, 2014 at 02:40:15PM -0700, Stephen Boyd wrote:
> On 05/24/14 05:48, Mark Brown wrote:
> > On Fri, May 23, 2014 at 12:57:17PM -0700, Stephen Boyd wrote:
> >
> >>  Optional properties:
> >> -- vdd-supply:	supply for Ethernet mac
> >> +- vdd-supply: analog 3.3V supply for Ethernet mac
> >> +- vdd-io-supply: digital 1.8V IO supply for Ethernet mac
> > 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. 

> > That said it looks like this is intended to be a supply for an external
> > PHY rather than the device itself, but even so my original question
> > about it being able to operate without power still applies.  Looking at
> > the code it's certainly not doing any of the handling of a missing
> > supply that I would associate with using _optional().
> 
> I agree, both supplies don't look optional. Unfortunately
> efm32gg-dk3750.dts doesn't look to be listing any supply, and this
> driver only recently got support for the VDD_A3.3 supply that the omap
> board uses (adding Uwe for any comments on efm setup). I presume on
If I read the schematic correctly there is nothing to regulate on the
efm32 dev board. If you want to take a look on the schematic yourself,
it's contained in the documentation package available at
http://www.silabs.com/products/mcu/lowpower/pages/efm32gg-dk3750.aspx .
BDR3201A_A02_sch.pdf, page 3 of 22.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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