Re: [PATCH v16 0/6] Device Tree support for FPGA programming

[atull <atull@opensource.altera.com>]

On Fri, 5 Feb 2016, atull@opensource.altera.com wrote:

> From: Alan Tull <atull@opensource.altera.com>
> 
> v16 Refactors the FPGA Area and FPGA Bus into single thing called an
> FPGA Region and eliminates using simple-bus.  I'm using the word
> "region" as it's a term is used in the literature of both the major
> FPGA manufacturors.
> 
> Changes for v16:
> * Refactor the FPGA Area and FPGA Bus into a FPGA Region.
> * Don't use simple-bus.
> * FPGA Managers and FPGA Bridges are now specified by phandle using the 
>   "fpga-mgr" and "fpga-bridges" properties.  fpga-bridges can specify
>   more than one bridge.
> * Device Tree overlays should be targeted to a FPGA Region.
> * The overlays need only contain firmware-name and the child nodes.
> * To model a system containing >1 partial reconfiguration region,
>   an overlay could add FPGA Regions to the base FPGA Regions.
> * Child FPGA Regions inherit the parent FGPA Manager, but specify
>   their own set of bridges if needes as partial reconfig regions
>   will likely need their own bridges.
> * All this is discussed in bindings/fpga/fpga-region.txt
> 
> One other highlight:
> The little engine that runs this thing is a reconfig notifier
> in fpga-region.c.  This notifier that will program an FPGA if a
> "firmware-name" property gets added to a fpga-region.  Then
> it will call of_platform_populate().  The current behavior in Linux
> when a DT overlay is applied is that the reconfig notifications
> go out in heirarchical order: first notifications are for the
> properties, then notifications for the child nodes.  So an overlay
> that adds a 'firmware-name' property and some child nodes to a
> fpga-region will cause FPGA programming and child node
> populating in the right order.

I figured out how to get rid of the reconfig notifier.

> 
> One issue with the dynamic DT stuff:
> I've tried returning and error from the notifier if FPGA programming
> fails; the error is noted on the console, but the child nodes
> get probed anyway.

I looked into it further and now I've got a solution for this issue
that I can post soon.  I can stop using the DT overlay configfs
interface and add a sysfs file for applying an overlay to an FPGA
region.  The FPGA region implementation will see the overlay before it
becomes part of the live tree.  Then it can do the FPGA programming
and see that succeed before the child nodes become part of the live
tree.  If FPGA programming fails, the overlay will be rejected before
it becomes part of the live tree.  By the time 'firmware-name' and the
child nodes show up in the live tree, they will be post-configuration
information.

Each fpga_region appears in sysfs and will add a file for loading the
overlay targeted to that region.  Such as:

echo fpga-dt-overlay.dtb.o > \
  /sys/class/fpga_region/region0/overlay_name

fpga-region.c's overlay_name attribute code will load the overlay
file, unflatten and resolve it.  Then it will check to make sure it
passes a few rules.  Such as: the overlay must contain a fragment that
is targeted to the region whose sysfs it was applied.

If the overlay passes the rules check, the FPGA region will program
the FPGA.  If that succeeds, then it calls of_overlay_create() and the
overlay is added into the live tree and the children get populated.

So fpga-region.c will ensure that the FPGA is already programmed
before the child nodes are added to the DT.

This solution also means that fpga-region.c no longer needs a reconfig
notifier.

I'll have to look at the documentation to see how that changes how I
talk about the bindings.  The documentation will have to become two
files again since part of this is Linux specific and part is DT
bindings.

Alan

> 
> 
> Alan Tull (6):
>   fpga: add bindings document for fpga region
>   add sysfs document for fpga bridge class
>   ARM: socfpga: add bindings document for fpga bridge drivers
>   fpga: add fpga bridge framework
>   fpga: fpga-region: device tree control for FPGA
>   ARM: socfpga: fpga bridge driver support
> 
>  Documentation/ABI/testing/sysfs-class-fpga-bridge  |   11 +
>  .../bindings/fpga/altera-fpga2sdram-bridge.txt     |   15 +
>  .../bindings/fpga/altera-hps2fpga-bridge.txt       |   47 ++
>  .../devicetree/bindings/fpga/fpga-region.txt       |  348 +++++++++++++++
>  drivers/fpga/Kconfig                               |   21 +
>  drivers/fpga/Makefile                              |    7 +
>  drivers/fpga/altera-fpga2sdram.c                   |  174 ++++++++
>  drivers/fpga/altera-hps2fpga.c                     |  213 +++++++++
>  drivers/fpga/fpga-bridge.c                         |  388 +++++++++++++++++
>  drivers/fpga/fpga-region.c                         |  460 ++++++++++++++++++++
>  include/linux/fpga/fpga-bridge.h                   |   55 +++
>  11 files changed, 1739 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-class-fpga-bridge
>  create mode 100644 Documentation/devicetree/bindings/fpga/altera-fpga2sdram-bridge.txt
>  create mode 100644 Documentation/devicetree/bindings/fpga/altera-hps2fpga-bridge.txt
>  create mode 100644 Documentation/devicetree/bindings/fpga/fpga-region.txt
>  create mode 100644 drivers/fpga/altera-fpga2sdram.c
>  create mode 100644 drivers/fpga/altera-hps2fpga.c
>  create mode 100644 drivers/fpga/fpga-bridge.c
>  create mode 100644 drivers/fpga/fpga-region.c
>  create mode 100644 include/linux/fpga/fpga-bridge.h
> 
> -- 
> 1.7.9.5
> 
>