Re: [PATCH v3 14/21] fpga: dfl: add fpga manager platform driver for FME

[Alan Tull]

On Mon, Feb 5, 2018 at 7:47 PM, Wu Hao <hao.wu@xxxxxxxxx> wrote:
> On Mon, Feb 05, 2018 at 10:36:45AM -0800, Luebbers, Enno wrote:
>> Hi Hao,
>>
>> On Sun, Feb 04, 2018 at 05:37:06PM +0800, Wu Hao wrote:
>> > 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@xxxxxxxxx> 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@xxxxxxxxx>
>> > > > > > Signed-off-by: Enno Luebbers <enno.luebbers@xxxxxxxxx>
>> > > > > > Signed-off-by: Shiva Rao <shiva.rao@xxxxxxxxx>
>> > > > > > Signed-off-by: Christopher Rauer <christopher.rauer@xxxxxxxxx>
>> > > > > > Signed-off-by: Kang Luwei <luwei.kang@xxxxxxxxx>
>> > > > > > Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
>> > > > > > Signed-off-by: Wu Hao <hao.wu@xxxxxxxxx>
>> > > > > > ----
>> > > > > > 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@xxxxxxxxx>
>> > > > > > +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.
>> > > >
>> > >
>> > > 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.
>> > >
>> > > 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).
>> >
>> > Hi Enno
>> >
>> > Yes, this interface is under fpga-dfl-fme-mgr.0, and fpga-dfl-fme-mgr.0 is
>> > under fpga-dfl-fme.0. It's part of the FME device for sure. From another
>> > point of view, it means if anyone wants to do PR on this Intel FPGA device,
>> > he needs to find the FME device firstly, and then check if any fpga manager
>> > created under this FME device, if yes, check the interface_id before PR via
>> > the FME device node ioctl.
>>
>> That sounds good, thank you!
>>
>> >
>> > >
>> > > Sorry for my limited understanding of the infrastructure - would this same
>> > > "fpga-dfl-fme-mgr.0" be used for PR if we had multiple PR regions? In that case
>> > > it would need to expose multiple interface_ids (or we'd have to track both
>> > > interface IDs and an identifier for the target PR region).
>> >
>> > Yes, the fpga manager could be shared with different PR regions.
>> >
>> > Sorry, I'm not sure where we need to expose multiple interface_ids and why.
>>
>> It's basically a question of how to determine bitstream compatibility - either,
>> there's a separate interface_id per reconfigurable region, or there is a single
>> interface_id for the entire device. Both make sense from a certain perspective.
>>
>> If there are multiple interface_ids per device (one per region), the driver
>> would need to expose all of them. If there's only a single one, the driver only
>> exposes that one ID - compatibility would be determined by looking at both that
>> single interface_id _and_ the identifier/number of the targeted region.
>>
>> I would prefer a separate interface_id per region - it seems more generic and
>> flexible.

Hi Enno,

I agree with this.

>
> It's possible to have per region interface_id (or even both per dev interface_id
> and per region interface_id at the same time), but per FME PR sub feature
> implementation, it supports multiple PR regions, but only provide one interface
> id, so at least in this case, it's not per-region information per my
> understanding. We can consider it later when hardware really supports it. : )

Hi Hao,

I understand that in the case of this PR hardware, the region to
program is selected when the region_id to program is written to a PR
hardware control register.  For another example, Arria10 has a hard PR
hardware and the PR bitstream lands in the area of the FPGA for which
it was compiled.  In that case, for the PR bitstream to be compatible
with a PR region, the layout of the edge connections also needs to be
compatible, so compatibility is per-region in that case instead of
per-PR hardware.   And besides, as I said yesterday, the hard PR
hardware would not know what the static region ID is when this
framework is used with such a device.

That's why I think making the id per-region may be more future proof,
even if it may see unnecessary in the case of the original blue bits
this was written for.

Alan