Message-ID: <524F04FD.5020804@zytor.com>
Date: Fri, 04 Oct 2013 11:12:13 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: monstr@monstr.eu
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Pavel Machek <pavel@denx.de>, Michal Simek <michal.simek@xilinx.com>,
        linux-kernel@vger.kernel.org, Alan Tull <atull@altera.com>,
        Dinh Nguyen <dinguyen@altera.com>,
        Philip Balister <philip@balister.org>,
        Alessandro Rubini <rubini@gnudd.com>,
        Steffen Trumtrar <s.trumtrar@pengutronix.de>,
        Jason Gunthorpe <jgunthorpe@obsidianresearch.com>,
        Jason Cooper <jason@lakedaemon.net>,
        Yves Vandervennet <rocket.yvanderv@gmail.com>,
        Kyle Teske <kyle.teske@ni.com>, Josh Cartwright <joshc@eso.teric.us>,
        Nicolas Pitre <nico@linaro.org>,
        Mark Langsdorf <mark.langsdorf@calxeda.com>,
        Felipe Balbi <balbi@ti.com>, linux-doc@vger.kernel.org,
        Mauro Carvalho Chehab <m.chehab@samsung.com>,
        David Brown <davidb@codeaurora.org>, Rob Landley <rob@landley.net>,
        "David S. Miller" <davem@davemloft.net>, Joe Perches <joe@perches.com>,
        Cesar Eduardo Barros <cesarb@cesarb.net>,
        Samuel Ortiz <sameo@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH v2 0/1] FPGA subsystem core
References: <cover.1380727889.git.michal.simek@xilinx.com> <524C6D64.8080801@zytor.com> <20131003064915.GB17155@amd.pavel.ucw.cz> <524EC965.70701@monstr.eu> <20131004141646.GA9396@kroah.com> <d700a91e-1319-4c35-895d-55e323c40703@email.android.com> <524ED081.1040600@monstr.eu> <524EF0CE.4040002@zytor.com> <524EFE76.70200@monstr.eu>
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On 10/04/2013 10:44 AM, Michal Simek wrote:
> 
> If you look at it in general I believe that there is wide range of 
> applications which just contain one bitstream per fpga and the 
> bitstream is replaced by newer version in upgrade. For them 
> firmware interface should be pretty useful. Just setup firmware 
> name with bitstream and it will be automatically loaded in startup 
> phase.
> 
> Then there is another set of applications especially in connection 
> to partial reconfiguration where this can be done statically by 
> pregenerated partial bitstreams or automatically generated on 
> target cpu. For doing everything on the target firmware interface 
> is not the best because everything can be handled by user 
> application and it is easier just to push this bitstream to do 
> device and not to save it to the fs.
> 
> I think the question here is if this subsystem could have several 
> interfaces. For example Alan is asking for adding char support. 
> Does it even make sense to have more interfaces with the same 
> backend driver? When this is answered then we can talk which one 
> make sense to have. In v2 is sysfs and firmware one. Adding char
> is also easy to do.
> 

Greg, what do you think?

I agree that the firmware interface makes sense when the use of the
FPGA is an implementation detail in a fixed hardware configuration,
but that is a fairly restricted use case all things considered.

	-hpa

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