Date:   Tue, 6 Feb 2018 13:23:15 +0800
From:   Wu Hao <hao.wu@...el.com>
To:     Alan Tull <atull@...nel.org>
Cc:     Moritz Fischer <mdf@...nel.org>,
        "Luebbers, Enno" <enno.luebbers@...el.com>,
        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>,
        Tim Whisonant <tim.whisonant@...el.com>,
        Shiva Rao <shiva.rao@...el.com>,
        Christopher Rauer <christopher.rauer@...el.com>,
        Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Subject: Re: [PATCH v3 14/21] fpga: dfl: add fpga manager platform driver for
 FME

On Mon, Feb 05, 2018 at 10:25:27PM -0600, Alan Tull wrote:
> On Mon, Feb 5, 2018 at 8:17 PM, Wu Hao <hao.wu@...el.com> wrote:
> > On Mon, Feb 05, 2018 at 11:21:52AM -0600, Alan Tull wrote:
> >> On Sun, Feb 4, 2018 at 4:05 AM, Wu Hao <hao.wu@...el.com> wrote:
> >> > On Sat, Feb 03, 2018 at 11:41:24AM +0100, Moritz Fischer wrote:
> >> >> Hi Hao,
> >> >>
> >> >> On Fri, Feb 02, 2018 at 04:26:26PM -0800, Luebbers, Enno wrote:
> >> >> > Hi Hao, Alan,
> >> >> >
> >> >> > On Fri, Feb 02, 2018 at 05:42:13PM +0800, Wu Hao wrote:
> >> >> > > On Thu, Feb 01, 2018 at 04:00:36PM -0600, Alan Tull wrote:
> >> >> > > > On Mon, Nov 27, 2017 at 12:42 AM, Wu Hao <hao.wu@...el.com> wrote:
> >> >> > > >
> >> >> > > > Hi Hao,
> >> >> > > >
> >> >> > > > A few comments below.   Besides that, looks good.
> >> >> > > >
> >> >> > > > > This patch adds fpga manager driver for FPGA Management Engine (FME). It
> >> >> > > > > implements fpga_manager_ops for FPGA Partial Reconfiguration function.
> >> >> > > > >
> >> >> > > > > Signed-off-by: Tim Whisonant <tim.whisonant@...el.com>
> >> >> > > > > Signed-off-by: Enno Luebbers <enno.luebbers@...el.com>
> >> >> > > > > Signed-off-by: Shiva Rao <shiva.rao@...el.com>
> >> >> > > > > Signed-off-by: Christopher Rauer <christopher.rauer@...el.com>
> >> >> > > > > Signed-off-by: Kang Luwei <luwei.kang@...el.com>
> >> >> > > > > Signed-off-by: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
> >> >> > > > > Signed-off-by: Wu Hao <hao.wu@...el.com>
> >> >> > > > > ----
> >> >> > > > > v3: rename driver to dfl-fpga-fme-mgr
> >> >> > > > >     implemented status callback for fpga manager
> >> >> > > > >     rebased due to fpga api changes
> >> >> > > > > ---
> >> >> > > > >  .../ABI/testing/sysfs-platform-fpga-dfl-fme-mgr    |   8 +
> >> >> > > > >  drivers/fpga/Kconfig                               |   6 +
> >> >> > > > >  drivers/fpga/Makefile                              |   1 +
> >> >> > > > >  drivers/fpga/fpga-dfl-fme-mgr.c                    | 318 +++++++++++++++++++++
> >> >> > > > >  drivers/fpga/fpga-dfl.h                            |  39 ++-
> >> >> > > > >  5 files changed, 371 insertions(+), 1 deletion(-)
> >> >> > > > >  create mode 100644 Documentation/ABI/testing/sysfs-platform-fpga-dfl-fme-mgr
> >> >> > > > >  create mode 100644 drivers/fpga/fpga-dfl-fme-mgr.c
> >> >> > > > >
> >> >> > > > > diff --git a/Documentation/ABI/testing/sysfs-platform-fpga-dfl-fme-mgr b/Documentation/ABI/testing/sysfs-platform-fpga-dfl-fme-mgr
> >> >> > > > > new file mode 100644
> >> >> > > > > index 0000000..2d4f917
> >> >> > > > > --- /dev/null
> >> >> > > > > +++ b/Documentation/ABI/testing/sysfs-platform-fpga-dfl-fme-mgr
> >> >> > > > > @@ -0,0 +1,8 @@
> >> >> > > > > +What:          /sys/bus/platform/devices/fpga-dfl-fme-mgr.0/interface_id
> >> >> > > > > +Date:          November 2017
> >> >> > > > > +KernelVersion:  4.15
> >> >> > > > > +Contact:       Wu Hao <hao.wu@...el.com>
> >> >> > > > > +Description:   Read-only. It returns interface id of partial reconfiguration
> >> >> > > > > +               hardware. Userspace could use this information to check if
> >> >> > > > > +               current hardware is compatible with given image before FPGA
> >> >> > > > > +               programming.
> >> >> > > >
> >> >> > > > I'm a little confused by this.  I can understand that the PR bitstream
> >> >> > > > has a dependency on the FPGA's static image, but I don't understand
> >> >> > > > the dependency of the bistream on the hardware that is used to program
> >> >> > > > the bitstream to the FPGA.
> >> >> > >
> >> >> > > Sorry for the confusion, the interface_id is used to indicate the version of
> >> >> > > the hardware for partial reconfiguration (it's part of the static image of
> >> >> > > the FPGA device). Will improve the description on this.
> >> >>
> >> >> I'm not sure userland should be making the call on whether what you're
> >> >> trying to load is compatible or not.
> >>
> >> Could you explain more about what your concern was about this (unless
> >> Hao has covered it below)?
> >>
> >> It makes sense to me in this use case at least since userspace has a
> >> pile of images and is choosing which one to load.
> >>
> >> >> Isn't there a way to check this in
> >> >> your PR reconfiguration handler in-kernel?
> >> >
> >> > Hi Moritz
> >> >
> >> > Actually with current driver interface, doing a partial reconfiguration with an
> >> > incompatible image, then driver will report PR failure with error code
> >> > FPGA_MGR_STATUS_INCOMPATIBLE_IMAGE_ERR as hardware checks it, but anyway user
> >> > needs to know hardware interface_id information to find or re-generated correct
> >> > images. I think it's more flexible to leave it to userspace on using this
> >> > information exposed by driver. : )
> >> >
> >> > Thanks
> >> > Hao
> >> >
> >> >>
> >> >> > >
> >> >> >
> >> >> > The interface_id expresses the compatibility of the static region with PR
> >> >> > bitstreams generated for it. It changes every time a new static region is
> >> >> > generated.
> >>
> >> In the near future the DFL framework will be used with SoC's that have
> >> a hard FPGA PR manager (that's not part of the static region).  The
> >> hard FPGA manager driver won't know anything about the static region.
> >>
> >> >> >
> >> >> > Would it make more sense to have the interface_id exposed as part of the FME
> >> >> > device (which represents the static region)? I'm not sure - it kind of also
> >> >> > makes sense here, where you would have all the information in one place (if the
> >> >> > interface_id matches, I can use this component to program a bitstream).
> >>
> >> According to the intel-fpga.txt document, the identifier for the
> >> static image is at
> >>
> >> /sys/class/fpga_region/regionX/fpga-dfl-fme.n/bitstream_id
> >
> > Hi Alan
> 
> Hi Hao,
> 
> >
> > This bitstream_id refects the full static region version. As you know, PR is
> > only a sub feature of the FME functional unit, it's possible that we have
> > different static region (different bitstream_id) but it has the exact same
> > PR sub feature under the FME, only changes on other sub features or function
> > units.
> 
> OK, thanks for that explanation.  That makes sense but could have
> easily been different.  Please document this somewhere.

Sure, will do.

Thanks
Hao

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