linux-kernel - Re: [PATCH v2 01/22] docs: fpga: add a document for Intel FPGA driver overview

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Date:   Fri, 14 Jul 2017 16:59:16 -0700
From:   "Luebbers, Enno" <enno.luebbers@...el.com>
To:     Wu Hao <hao.wu@...el.com>
Cc:     Alan Tull <atull@...nel.org>, Moritz Fischer <mdf@...nel.org>,
        linux-fpga@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org, "Kang, Luwei" <luwei.kang@...el.com>,
        "Zhang, Yi Z" <yi.z.zhang@...el.com>,
        Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Subject: Re: [PATCH v2 01/22] docs: fpga: add a document for Intel FPGA
 driver overview

On Thu, Jul 13, 2017 at 12:25:20PM +0800, Wu Hao wrote:
> On Wed, Jul 12, 2017 at 09:51:32AM -0500, Alan Tull wrote:
> > On Sun, Jun 25, 2017 at 8:51 PM, Wu Hao <hao.wu@...el.com> wrote:
> > 
> > Hi Hao,
> > 
> > > Add a document for Intel FPGA driver overview.
> > >
> > > Signed-off-by: Enno Luebbers <enno.luebbers@...el.com>
> > > Signed-off-by: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
> > > Signed-off-by: Wu Hao <hao.wu@...el.com>
> > > ----
> > > v2: added FME fpga-mgr/bridge/region platform driver to driver organization.
> > >     updated open discussion per current implementation.
> > >     fixed some typos.
> > > ---
> > >  Documentation/fpga/intel-fpga.txt | 256 ++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 256 insertions(+)
> > >  create mode 100644 Documentation/fpga/intel-fpga.txt
> > >
> > > diff --git a/Documentation/fpga/intel-fpga.txt b/Documentation/fpga/intel-fpga.txt
> > > new file mode 100644
> > > index 0000000..4a29470
> > > --- /dev/null
> > > +++ b/Documentation/fpga/intel-fpga.txt
> > > @@ -0,0 +1,256 @@
> > > +===============================================================================
> > > +                    Intel FPGA driver Overview
> > > +-------------------------------------------------------------------------------
> > > +                Enno Luebbers <enno.luebbers@...el.com>
> > > +                Xiao Guangrong <guangrong.xiao@...ux.intel.com>
> > > +                Wu Hao <hao.wu@...el.com>
> > > +
> > > +The Intel FPGA driver provides interfaces for userspace applications to
> > > +configure, enumerate, open, and access FPGA accelerators on platforms equipped
> > > +with Intel(R) FPGA PCIe based solutions and enables system level management
> > > +functions such as FPGA reconfiguration, power management, and virtualization.
> > > +
> > > +HW Architecture
> > > +===============
> > > +From the OS's point of view, the FPGA hardware appears as a regular PCIe device.
> > > +The FPGA device memory is organized using a predefined data structure (Device
> > > +Feature List). Features supported by the particular FPGA device are exposed
> > > +through these data structures, as illustrated below:
> > > +
> > > +  +-------------------------------+  +-------------+
> > > +  |              PF               |  |     VF      |
> > > +  +-------------------------------+  +-------------+
> > > +      ^            ^         ^              ^
> > > +      |            |         |              |
> > > ++-----|------------|---------|--------------|-------+
> > > +|     |            |         |              |       |
> > > +|  +-----+     +-------+ +-------+      +-------+   |
> > > +|  | FME |     | Port0 | | Port1 |      | Port2 |   |
> > > +|  +-----+     +-------+ +-------+      +-------+   |
> > > +|                  ^         ^              ^       |
> > > +|                  |         |              |       |
> > > +|              +-------+ +------+       +-------+   |
> > > +|              |  AFU  | |  AFU |       |  AFU  |   |
> > > +|              +-------+ +------+       +-------+   |
> > > +|                                                   |
> > > +|                 FPGA PCIe Device                  |
> > > ++---------------------------------------------------+
> > > +
> > > +The driver supports PCIe SR-IOV to create virtual functions (VFs) which can be
> > > +used to assign individual accelerators to virtual machines.
> > > +
> > > +FME (FPGA Management Engine)
> > > +============================
> > > +The FPGA Management Engine performs power and thermal management, error
> > > +reporting, reconfiguration, performance reporting, and other infrastructure
> > > +functions. Each FPGA has one FME, which is always accessed through the physical
> > > +function (PF).
> > > +
> > > +User-space applications can acquire exclusive access to the FME using open(),
> > > +and release it using close().
> > > +
> > > +The following functions are exposed through ioctls:
> > > +
> > > +       Get driver API version (FPGA_GET_API_VERSION)
> > > +       Check for extensions (FPGA_CHECK_EXTENSION)
> > > +       Assign port to PF (FPGA_FME_PORT_ASSIGN)
> > > +       Release port from PF (FPGA_FME_PORT_RELEASE)
> > > +       Program bitstream (FPGA_FME_PORT_PR)
> > > +
> > 
> > I was hoping the API mailing list might have an opinion about this,
> > but I think adding ioctls to the kernel is discouraged.  Could these
> > be sysfs?
> 
> Hi Alan,
> 
> As you see below, we have defined a lot of sysfs interface for device
> info, attributes and simple control operations. But for some actions
> which requires complex inputs/outputs parameters (e.g a struct with
> multiple items) with userspace, ioctls are used. I feel in such cases,
> ioctls seem more suitable than sysfs.
> 

Also, we're thinking that some operations require that you first "acquire
ownership" of the respective device, which I believe maps more easily to
open() and ioctls than sysfs.

Thanks
- Enno