Re: [PATCH v14 1/7] fpga: add usage documentation for fpga area

[Rob Herring]

On Thu, Dec 10, 2015 at 05:37:03PM -0600, atull@xxxxxxxxxxxxxxxxxxxxx wrote:
> From: Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx>
> 
> Add a document spelling out usage of the FPGA Area for
> reprogramming FPGA's under Device Tree control.
 
I'm not too sure about the split between this and the binding doc. This 
one clears up a bit after reading the binding doc first and most of this 
is about DT.

> Signed-off-by: Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx>
> 
> ---
> v9:  Initial version of this patch in patchset
> v10: s/fpga/FPGA/g
>      improve formatting
>      some rewriting
>      move to staging/simple-fpga-bus
> v11: No change in this patch for v11 of the patch set
> v12: Moved out of staging
>      Small changes due to using FPGA bridge framework and not
>      representing the bridges as resets.
> v13: Fix some nits
> v14: fpga-area instead of simple-fpga-bus
> ---
>  Documentation/fpga/fpga-area.txt |  299 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 299 insertions(+)
>  create mode 100644 Documentation/fpga/fpga-area.txt
> 
> diff --git a/Documentation/fpga/fpga-area.txt b/Documentation/fpga/fpga-area.txt
> new file mode 100644
> index 0000000..f031522
> --- /dev/null
> +++ b/Documentation/fpga/fpga-area.txt
> @@ -0,0 +1,299 @@
> +FPGA Area
> +
> +Alan Tull 2015
> +
> +Overview
> +========
> +
> +An FPGA Area details information about a section of an FPGA including the FPGA
> +image needed to program it and the hardware contained once it is programmed.
> +
> +Loading a Device Tree overlay which contains an FPGA Area will cause the
> +FPGA to be programmed and the children of the FPGA Area will get probed.
> +
> +There may be FPGA Bridges involved to prevent spurious data from going out onto
> +the processor bus during FPGA programming.  If so, the FPGA Area will need to
> +disable and enable bridges that will only affect the child devices that are
> +below the FPGA Area.  In the case of partial reconfiguration, bridges will
> +be required within the FPGA design such that the active sections of the
> +FPGA are on the bus while sections that are not programmed or being
> +reprogrammed at the moment are isolated.
> +
> +Removing the overlay will result in the child devices getting removed and the
> +bridges disabled.  Note that in the case of partial reconfiguration the rest of
> +the FPGA continues to function as normal while this is happening.
> +
> +Below are more details on the structuring of the Device Tree for this.
> +
> +Terminology
> +===========
> +
> +Full Reconfiguration
> + * The entire FPGA is reprogrammed.
> +
> +Partial Reconfiguration (PR)
> + * Part of the FPGA is reprogrammed while the rest of the FPGA is live and
> +   active.  Not all FPGA's support this.
> +
> +Associated Blocks
> +=================
> +
> +FPGA Manager Framework
> + * An FPGA Manager is a hardware block that programs an FPGA under the control
> +   of a host processor.
> + * The FPGA Manager Framework provides drivers and functions to program an
> +   FPGA.
> +
> +FPGA Bridge Framework
> + * Provides drivers and functions to control bridges that enable/disable
> +   data to the FPGA.
> + * FPGA bridges should be disabled while the FPGA is being programmed to
> +   prevent spurious data on the bus.
> + * FPGA bridges are not needed in implementations where the FPGA Manager
> +   handles this.
> +
> +Device Tree
> +===========
> +
> +For the purposes of this document, I'm dividing the Device Tree (DT) into two parts,
> +each with its own requirements.  The two parts are:
> + * The live DT prior to the overlay being added
> + * The overlay containing an FPGA Area
> +
> +The live DT will contain:
> + * FPGA Manager
> + * FPGA Bridges as children of the FPGA Manager (optional, architecture specific)
> +
> +The live Device Tree must contain an FPGA Manager to handle programming the FPGA.
> +If FPGA Bridges need to be involved, they show up in the DT as direct children
> +of the FPGA Manager.  During full reconfiguration, the FPGA Area will disable
> +any bridges that are direct children of the manager during full reconfiguration
> +and will re-enable them afterwards.
> +
> +The insertion point in the live tree will also need the "simple-bus"
> +compatibility string to enable populating the child nodes for the overlay.
> +That includes the nodes for the FPGA Manager and controlling FPGA Bridges
> +as explained below.
> +
> +The Device Tree Overlay will contain:
> + * "target-path"
> +   The insertion point where the the contents of the overlay will go into the
> +   live tree.
> + * "ranges"
> + * "firmware-name"
> +   Specifies the name of the FPGA image file on the firmware search
> +   path.  The search path is described in the firmware class documentation.
> + * "partial-reconfig"
> +   This binding is a boolean and should be present if partial reconfiguration
> +   is to be done.
> + * child nodes corresponding to hardware that will be loaded in this
> +   region of the FPGA.
> +
> +Supported use models
> +====================
> +
> +Here's a list of the superset of supported use models.  We may need to add
> +more.  Some uses are specific to one FPGA or another.
> +
> + * No FPGA Bridges
> +   In this case, the FPGA Manager which programs the FPGA also handles the
> +   bridges and no FPGA Bridge devices are needed for full reconfiguration.
> +
> +   The DT overlay will specify the FPGA Manager as the overlay target.
> +
> + * Full reconfiguration with bridges
> +   In the case, there are several bridges between the processor and FPGA,
> +   that need to be disabled during full reconfiguration.
> +   The DT before the overlay is applied will have an FPGA Manager.  The
> +   immediate children of the manager will be the FPGA Bridges that need to be
> +   disabled during FPGA programming.
> +
> +   The DT overlay will specify one of those bridges as the overlay target,
> +   typically the bridge that allows memory mapped register access ("the
> +   controlling bridge").
> +
> + * Partial reconfiguration with bridges in the FPGA
> +   In this case, the FPGA can have more than one section that will be
> +   reprogrammed separately.  Other sections may be active on the bus while FPGA
> +   is being programmed.  To manage this, FPGA Bridges need to exist on the FPGA
> +   that can freeze all the buses going to one FPGA area while the buses are
> +   enabled for other sections.
> +
> +Controlling Bridge
> +==================
> +
> +It is possible that there are multiple FPGA Bridges connecting the processor
> +and FPGA.  In a text based hierarchy, it is difficult to show this properly
> +so what we do is consider the bridge that handles register access to be
> +the controlling bridge.  The overlay is targeted to be inserted under the
> +controlling bridge.  Other bridges are on the same level of the device tree
> +as the controlling bridge, i.e. all are children of the FPGA Manager.  The
> +ranges property handles mapping memory ranges through multiple bridges.
> +
> +Sequence
> +========
> +
> +Load the DT overlay.  One way to do that from user space is to use Pantelis
> +Antoniou's DT-Overlay configfs interface.  In that case the sequence from
> +userspace is:

It will be a problem merging this series if you document things that are 
not upstream yet.

> +
> + $ mkdir /config/device-tree/overlays/1
> + $ echo "some_overlay.dtb.o" > /config/device-tree/overlays/1/path
> +
> +This causes the FPGA Area to be probed and will do the following:
> + 1. Disable the FPGA bridges.
> + 2. Use the the FPGA manager core to program the FPGA.
> + 3. Enable the FPGA bridges.
> + 4. Call of_platform_populate resulting in device drivers getting probed.
> +
> +Removing the overlay is done by:
> +
> + $ rmdir /config/device-tree/overlays/1
> +
> +This causes the child nodes to be removed and then the bridges are disabled.
> +
> +Device Tree Examples
> +====================
> +
> +The intention of this section is to give some simple examples, focusing on
> +the placement of the elements detailed above in, especially:
> + * FPGA Managers
> + * FPGA Bridges in some cases
> + * FPGA Areas and associated properties
> + * simple-bus
> + * ranges
> + * target-path
> +
> +Please note the "simple-bus" compatible string added for FPGA Managers and for
> +FPGA Bridges where the overlay is targeted for insertion.  This is required for
> +populating the child nodes.
> +
> +Device Tree Example: Partial Reconfiguration with no Bridges
> +============================================================
> +
> +Live Device Tree contains:
> +	fpgamgr@0 {

Unit address should be ffd03000 here.

> +		compatible = "altr,socfpga-a10-fpga-mgr", "simple-bus";

This should not have simple-bus. This would be broken in the case of 
applying the overlay before booting the kernel. You don't want the 
devices probed before the fpgamgr has programmed them.

> +		clocks = <&l4_mp_clk>;
> +		resets = <&rst FPGAMGR_RESET>;
> +		reset-names = "fpgamgr";
> +		reg = <0xffd03000 0x1000
> +		       0xffcfe400 0x1000>;
> +
> +		#address-cells = <0x1>;
> +		#size-cells = <0x1>;
> +		ranges;
> +	};
> +
> +DT Overlay contains:
> +/dts-v1/;
> +/plugin/;
> +/ {
> +	fragment@0 {
> +		target-path="/soc/fpgamgr@0";  /* targeted to the manager */
> +		__overlay__ {
> +			#address-cells = <1>;
> +	                #size-cells = <1>;
> +
> +			area@0 {
> +				compatible = "fpga-area";
> +
> +				#address-cells = <1>;
> +				#size-cells = <1>;
> +				ranges = <0x10010 0xff210010 0x10>;
> +
> +				firmware-name = "fit_pr_v1.rbf";
> +				partial-reconfig;
> +
> +				gpio@0x100010010 {

Remove 0x

> +					compatible = "altr,pio-1.0";
> +					reg = <0x10010 0x10>;
> +					altr,ngpio = <4>;
> +					#gpio-cells = <0x2>;
> +					gpio-controller;
> +				};
> +			};
> +		};
> +	};
> +};
> +
> +
> +Device Tree Example: Full Reconfiguration with Bridges
> +======================================================
> +
> +Live Device Tree contains:
> +	fpgamgr@0 {

unit address

> +		compatible = "altr,socfpga-fpga-mgr", "simple-bus";
> +		reg = <0xFF706000 0x1000
> +		       0xFFB90000 0x1000>;

lower case

> +		interrupts = <0 175 4>;
> +
> +		#address-cells = <0x1>;
> +		#size-cells = <0x1>;
> +		ranges;
> +
> +		bridge@0 {

Don't the outbound bridges have an address range associated with them? 
Possibly, they should not be children of the fpgamgr unless the fpgamgr 
itself is a bridge.

> +			/* both the manager and the controlling bridge have
> +			 * the added simple-bus compatible to allow child
> +			 * devices to be populated. */

Why? Once you have initialized the bridge, you call of_platform_populate 
with this node as the starting point. The root does not need any 
matching string.

> +			compatible = "altr,socfpga-lwhps2fpga-bridge",
> +				     "simple-bus";
> +			resets = <&rst LWHPS2FPGA_RESET>;
> +			reset-names = "lwhps2fpga";
> +			clocks = <&l4_main_clk>;
> +			#address-cells = <0x1>;
> +			#size-cells = <0x1>;
> +			ranges;
> +		};
> +
> +		bridge@1 {
> +			/* In the case of full reconfiguration, both bridge@0
> +			 * and bridge@1 will be disabled during FPGA
> +			 * programming and enabled afterwards. */
> +			compatible = "altr,socfpga-hps2fpga-bridge";
> +			resets = <&rst HPS2FPGA_RESET>;
> +			reset-names = "hps2fpga";
> +			clocks = <&l4_main_clk>;
> +		};
> +	};
> +
> +DT Overlay contains:
> +/dts-v1/;
> +/plugin/;
> +/ {
> +	fragment@0 {
> +		target-path="/soc/fpgamgr@0/bridge@0"; /* controlling bridge */
> +		__overlay__ {
> +			#address-cells = <1>;
> +	                #size-cells = <1>;
> +
> +			area@0 {
> +				compatible = "fpga-area";
> +
> +				#address-cells = <2>;
> +				#size-cells = <1>;
> +				/* Note that two ranges are mapped due to the
> +				 * two bridges. */
> +				ranges = <0 0x00000000 0xc0000000 0x00010000>,
> +					 <1 0x00020000 0xff220000 0x00000008>;

0 and 1 are address bits or mean something else (chip select # is common 
example)?

> +
> +				firmware-name = "soc_system.rbf";
> +
> +				onchip_memory2_0: memory@000000000 {

Drop leading zeros (i.e. memory@0).

> +					device_type = "memory";
> +					compatible = "altr,onchipmem-15.1";
> +					reg = <0 0x00000000 0x00010000>;
> +				};
> +
> +				jtag_uart: serial@0x100020000 {

Drop '0x'

> +					compatible = "altr,juart-1.0";
> +					reg = <1 0x00020000 0x00000008>;
> +					interrupt-parent = <&intc>;
> +					interrupts = <0 42 4>;
> +					clocks = <&osc2>;
> +				};
> +			};
> +		};
> +	};
> +};
> +
> -- 
> 1.7.9.5
> 
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