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

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Message-ID: <CANk1AXSTMynxMrDZ=aHsoX4naqByJnsRXPBvRGTSBpv2_5WptQ@mail.gmail.com>
Date:   Wed, 15 Feb 2017 12:23:28 -0600
From:   Alan Tull <delicious.quinoa@...il.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     Moritz Fischer <moritz.fischer@...us.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-fpga@...r.kernel.org
Subject: Re: [RFC 7/8] fpga-region: add sysfs interface

On Wed, Feb 15, 2017 at 12:06 PM, Jason Gunthorpe
<jgunthorpe@...idianresearch.com> wrote:

Hi Jason,

> On Wed, Feb 15, 2017 at 11:46:01AM -0600, Alan Tull wrote:
>> I agree.  I've heard some discussions about adding a header.  We would
>> want it to not be manufacturer or fpga device specific. That would be
>> nice and would eliminate some of this struct.  We would need a tool to
>> add the header, given a bitstream and some info about the bitstream.
>> If the tool communicated seamlessly with vendor's tools that would be
>> nice, but that is complicated to get that to happen.  So far nobody
>> has posted their proposals to the mailing list.
>
> Okay, we've had success using a HTTP style plain text header for the
> last 15 years. Here is a header example:
>
> BIT/1.0
> Bit-Order: reversed
> Builder: jgg
> Content-Length: 9987064
> Date: Thu, 19 Jan 2017 06:22:42 GMT
> Design: tluna
> Device: 7k355t
> GIT-TOT: 60da4e9e8e9610e490ddeb4e5880778938f80691
> Package: ffg901
> Pad: xxxx
> Speed: 2
> Speed-File: PRODUCTION 1.12 2014-09-11
> Synplify-Ver: Pro I-2014.03-1 , Build 016R, Mar 24 2014
> Xilinx-Ver: Vivado v.2016.1 (lin64) Build 1538259 Fri Apr  8 15:45:23 MDT 2016
>
> [raw bitfile follows, start byte in the file is aligned for DMA]
>
> The plaintext format allows a fair amount of flexibility, eg I could
> include the linux header for partial/encrypt along with my usual
> headers for identification.
>
> So along those lines I'd suggest the basic Linux format to be
>
> Linux_FPGA_BIT/1.0
> FPGA-Device: xc7k355t-ffg901-2    # Allow the kernel driver to check, if it can
> # Enable partial reconfiguration and require the full bitfile to have
> # the ID 'xxx'
> Partial-Reconfiguration-Basis-ID: xxxx
> # This is a full bitfile with unique tag xxxx
> FPGA-ID: xxxx
> Encrypted: yes/no   # Enable decryption if the driver needs to be told
> Pad: xxxx           # Enough 'x' characters to align the bitfile
>
> [raw bitfile follows, start byte in the file is aligned for DMA]
>
> I can publish a version of my python script which produces these files
> from typical Xilinx output..
>
> The kernel could detect the bitfile starts with 'Linux_FPGA_BIT/1.0\n'
> and then proceed to decode the header providing compat with the
> current scheme.
>
> This is usually the sort of stuff I'd punt to userspace, but since the
> kernel is doing request_firmware it is hard to see how that is an
> option in this case...

I like how extensible (and readable!) this is.  It wouldn't take much
kernel code to add this.  I'd like to see the python script.

Alan

>
> Jason