linux-kernel - Re: [PATCH v4 2/6] arm: dts: socfpga: add altera fpga manager

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Date:	Wed, 10 Dec 2014 18:49:45 +0100
From:	Steffen Trumtrar <s.trumtrar@...gutronix.de>
To:	atull <atull@...nsource.altera.com>
Cc:	gregkh@...uxfoundation.org, jgunthorpe@...idianresearch.com,
	hpa@...or.com, monstr@...str.eu, michal.simek@...inx.com,
	rdunlap@...radead.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, pantelis.antoniou@...sulko.com,
	robh+dt@...nel.org, grant.likely@...aro.org, iws@...o.caltech.edu,
	linux-doc@...r.kernel.org, pavel@...x.de, broonie@...nel.org,
	philip@...ister.org, rubini@...dd.com, jason@...edaemon.net,
	kyle.teske@...com, nico@...aro.org, balbi@...com,
	m.chehab@...sung.com, davidb@...eaurora.org, rob@...dley.net,
	davem@...emloft.net, cesarb@...arb.net, sameo@...ux.intel.com,
	akpm@...ux-foundation.org, linus.walleij@...aro.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	delicious.quinoa@...il.com, dinguyen@...nsource.altera.com,
	yvanderv@...nsource.altera.com
Subject: Re: [PATCH v4 2/6] arm: dts: socfpga: add altera fpga manager

On Wed, Dec 10, 2014 at 11:25:59AM -0600, atull wrote:
> On Wed, 10 Dec 2014, Steffen Trumtrar wrote:
> 
> > Hi!
> > 
> > On Tue, Dec 09, 2014 at 02:14:46PM -0600, atull@...nsource.altera.com wrote:
> > > From: Alan Tull <atull@...nsource.altera.com>
> > > 
> > > Add Altera FGPA manager to device tree.
> > > 
> > > Signed-off-by: Alan Tull <atull@...nsource.altera.com>
> > > ---
> > >  arch/arm/boot/dts/socfpga.dtsi |   10 ++++++++++
> > >  1 file changed, 10 insertions(+)
> > > 
> > > diff --git a/arch/arm/boot/dts/socfpga.dtsi b/arch/arm/boot/dts/socfpga.dtsi
> > > index 4472fd9..bab98b6 100644
> > > --- a/arch/arm/boot/dts/socfpga.dtsi
> > > +++ b/arch/arm/boot/dts/socfpga.dtsi
> > > @@ -751,5 +751,15 @@
> > >  			compatible = "altr,sys-mgr", "syscon";
> > >  			reg = <0xffd08000 0x4000>;
> > >  		};
> > > +
> > > +		hps_0_fpgamgr: fpgamgr@...f706000 {
> > > +			compatible = "altr,fpga-mgr", "simple-bus";
> > > +			reg = <0xFF706000 0x1000
> > > +			       0xFFB90000 0x1000>;
> > > +			interrupts = <0 175 4>;
> > > +			#address-cells = <1>;
> > > +			#size-cells = <1>;
> > > +			ranges;
> > > +		};
> > 
> > The fpgamgr is NOT a bus. You don't need ranges and/or simple-bus.
> > 
> > Regards,
> > Steffen
> 
> Actually, I am going to be using this when I add the DT notification 
> stuff.  That stuff is waiting for DT overlays to show up in the main
> tree.
> 
> So the choice it to either change this file now, once, or do the minimal 
> changes and have to change it again later.
> 

Yes, that is what I thought. And still, devices can NOT show up
at the fpgamgr. They show up on the various bridges.

And as far as I understand the DT overlay stuff, you specify in
the overlay what the parent node will be.
For i2c this is one of the i2c-hosts, for spi one of the spi-hosts
and for IP cores in a bitstream one of the bridges.

The fpgamgr is, from my understanding, only responsible for writing
the bitstream to the FPGA; nothing more.

Regards,
Steffen

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