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SubjectRe: [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@intel.com> wrote:
> >
> > Hi Hao,
> >
> > > Add a document for Intel FPGA driver overview.
> > >
> > > Signed-off-by: Enno Luebbers <enno.luebbers@intel.com>
> > > Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> > > Signed-off-by: Wu Hao <hao.wu@intel.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@intel.com>
> > > + Xiao Guangrong <guangrong.xiao@linux.intel.com>
> > > + Wu Hao <hao.wu@intel.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

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