linux-kernel - Re: [PATCH v12 2/6] fpga: add bindings document for simple fpga bus

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Date:	Wed, 28 Oct 2015 08:18:43 -0700
From:	Moritz Fischer <moritz.fischer@...us.com>
To:	atull <atull@...nsource.altera.com>
Cc:	Steffen Trumtrar <s.trumtrar@...gutronix.de>,
	Greg KH <gregkh@...uxfoundation.org>,
	Josh Cartwright <joshc@...com>,
	Michal Simek <monstr@...str.eu>,
	Michal Simek <michal.simek@...inx.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
	Alan Tull <delicious.quinoa@...il.com>,
	"dinguyen@...nsource.altera.com" <dinguyen@...nsource.altera.com>
Subject: Re: [PATCH v12 2/6] fpga: add bindings document for simple fpga bus

On Wed, Oct 28, 2015 at 7:53 AM, atull <atull@...nsource.altera.com> wrote:

>> > +A Simple FPGA Bus is a bus that handles configuring an FPGA and its bridges
>> > +before populating the devices below its node.  All this happens when a device
>> > +tree overlay is added to the live tree.  This document describes that device
>> > +tree overlay.
>> > +
>>
>> This is not really true, is it?
>> The driver should work without applying the overlay, e.g. the bootloader
>> might have already done it.
>>
>
> Yes it's true.  I'm not clear what you are saying.  If the bootloader has
> programmed the FPGA, the overlay can leave out the optional properties
> and the FPGA won't get reprogrammed; the child devices will still get
> added and probed.  So this handles both the case where you want to reprogram
> the FPGA under Linux and where the FPGA was programmed by a bootloader.

I think what he means is that the document explicitly calls out the overlay,
when in theory it also works without an overlay. While being the most 'natural'
use-case, it is not the only one ;-)

Moritz
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