Re: [RFC 7/8] fpga-region: add sysfs interface

From: matthew.gerlach@linux.intel.com
To: Moritz Fischer <moritz.fischer@ettus.com>
Cc: "Alan Tull" <delicious.quinoa@gmail.com>,
	"Nadathur, Sundar" <sundar.nadathur@intel.com>,
	"Yves Vandervennet" <yves.vandervennet@linux.intel.com>,
	"Jason Gunthorpe" <jgunthorpe@obsidianresearch.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	"linux-fpga@vger.kernel.org" <linux-fpga@vger.kernel.org>,
	"Marek Vašut" <marex@denx.de>
Subject: Re: [RFC 7/8] fpga-region: add sysfs interface
Date: Mon, 27 Feb 2017 16:04:59 -0800 (PST)	[thread overview]
Message-ID: <alpine.DEB.2.20.1702271559340.23635@mgerlach-VirtualBox> (raw)
In-Reply-To: <CAAtXAHcc+kbGCHsixP2GhbrUKEE3XJZmS8QnYnteJNp2-zspxg@mail.gmail.com>

On Mon, 27 Feb 2017, Moritz Fischer wrote:

> Alan,
>
> On Mon, Feb 27, 2017 at 12:09 PM, Alan Tull <delicious.quinoa@gmail.com> wrote:
>
>
>> First case: embedded FPGA.  The hardware has one FPGA.  The image is
>> designed for a specific board, so there's no problem including the
>> enumeration in the image.
>
> Agreed.
>
>> Second case: embedded FPGA + a PCIe FPGA.  The image will be specific
>> as to whether it goes into the embedded FPGA or the PCIe one.
>
> Agreed.
>
>
>> Third case: multiple PCIe FPGAs.  The enumeration base will be the
>> PCIe bus of the individual FPGA.  If the FPGAs don't have unique pin
>> connections, then the images could go on any of the PCie FPGAs.  If
>> there are unique pin connections, then the image will be specific to
>> the FPGA and having the enumeration data in the image is that much
>> more helpful for keeping things straight.  Part of the header could
>> specify which specific FPGA it should go on if it is restricted.
>
> Agreed.
>
>> Of course if the FPGAs have > 1 PR regions, most FPGA architectures do
>> not have relocatable images so those images will be specific for the
>> PR region but not specific to the FPGA except as otherwise noted
>> above.
>>
>> So again, including enumeration data in the bitstream should work
>> unless I'm missing something.  What am I missing here?
>
> If you enumeration base is sufficiently smart, I suppose that can work.
> What you'd probably want is some sort of extension to the platform bus?

I think there is merit it considering the platform bus as part of the 
overal enumeration strategy.  When using device trees, the platform bus is 
involved.  I have also seen other folks enumerate over a platform bus 
based on data in a format other than device tree.  I have experimented 
with instantiating platform devices from my pcie driver, but I didn't 
completely work, which could be related to using a fairly old 3.10 kernel.

Matthew Gerlach

>
> I really need to take another look at how non-dt systems enumerate to
> give better feedback on this.
>
> Cheers,
>
> Moritz
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