linux-kernel - Re: [RFC PATCH 0/1] Portable Device Tree Connector -- conceptual

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Date:	Mon, 4 Jul 2016 11:15:44 -0700
From:	Frank Rowand <frowand.list@...il.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	robh+dt@...nel.org, david@...son.dropbear.id.au,
	pantelis.antoniou@...sulko.com, stephen.boyd@...aro.org,
	grant.likely@...retlab.ca, mark.rutland@....com,
	mporter@...sulko.com, koen@...inion.thruhere.net,
	linux@...ck-us.net, marex@...x.de, wsa@...-dreams.de,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-i2c@...r.kernel.org, panto@...oniou-consulting.com
Subject: Re: [RFC PATCH 0/1] Portable Device Tree Connector -- conceptual

On 07/04/16 08:22, Mark Brown wrote:
> On Sat, Jul 02, 2016 at 04:55:49PM -0700, frowand.list@...il.com wrote:
> 
>> This is an extremely simple example to illustrate the concepts.  It is not
>> meant to represent the complexity of a real board.
>>
>> To start with, assume that the device that will eventually be on a daughter
>> board is first soldered onto the mother board.  The mother board contains
>> two devices connected via bus spi_1.  One device is described in the .dts
>> file, the other is described in an included .dtsi file.
>> Then the device tree files will look like:
> 
> Can I suggest not using SPI as an example here?  It's particularly
> messy since addresses are essentially just a random signal that can be
> totally separate to the controller hardware which might be adding more
> complexity early on in building up your model than is really desirable.
> It will need to be dealt with but perhaps not right now.  I2C might be
> easier.
> 
> The initial issue with SPI is that you really need to do something like
> bring out individual slots on the bus rather than the bus as a whole
> since you're going to need a remapping layer to map chip selects on the
> module to chip selects on the host board.
> 

Yes, thank you for pointing that out.

For the purposes of the mental model, when thinking about what I wrote,
just change SPI to I2C everywhere.

-Frank