Re: [PATCH v9 3/7] staging: add bindings document for simple fpga bus

Steffen Trumtrar
2015-07-17T19:49:13Z

Hi!

On Fri, Jul 17, 2015 at 10:51:13AM -0500, atull@opensource.altera.com wrote:
> From: Alan Tull <atull@opensource.altera.com>
>
> New bindings document for simple fpga bus.
>
> Signed-off-by: Alan Tull <atull@opensource.altera.com>
> ---
> .../Documentation/bindings/simple-fpga-bus.txt | 61 ++++++++++++++++++++
> 1 file changed, 61 insertions(+)
> create mode 100644 drivers/staging/fpga/Documentation/bindings/simple-fpga-bus.txt
>
> diff --git a/drivers/staging/fpga/Documentation/bindings/simple-fpga-bus.txt b/drivers/staging/fpga/Documentation/bindings/simple-fpga-bus.txt
> new file mode 100644
> index 0000000..221e781
> --- /dev/null
> +++ b/drivers/staging/fpga/Documentation/bindings/simple-fpga-bus.txt
> @@ -0,0 +1,61 @@
> +Simple FPGA Bus
> +===============
> +
> +A Simple FPGA Bus is a bus that handles configuring an FPGA and its bridges
> +before populating the devices below its node.
> +
> +Required properties:
> +- compatible : should contain "simple-fpga-bus"
> +- #address-cells, #size-cells, ranges: must be present to handle address space
> + mapping for children.
> +
> +Optional properties:
> +- fpga-mgr : should contain a phandle to a fpga manager.
> +- fpga-firmware : should contain the name of a fpga image file located on the
> + firmware search path.
> +- partial-reconfig : boolean property should be defined if partial
> + reconfiguration is to be done.
> +- resets : should contain a list of resets that should be released after the
> + fpga has been programmed i.e. fpga bridges.
> +- reset-names : should contain a list of the names of the resets.
> +
> +Example:
> +
> +/dts-v1/;
> +/plugin/;
> +/ {
> + fragment@0 {
> + target-path="/soc";
> + __overlay__ {
> + #address-cells = <1>;
> + #size-cells = <1>;
> +
> + bridge@0xff200000 {
> + compatible = "simple-fpga-bus";
> + #address-cells = <0x2>;
> + #size-cells = <0x1>;
> + ranges = <0x1 0x10040 0xff210040 0x20>;
> +
> + clocks = <0x2 0x2>;
> + clock-names = "h2f_lw_axi_clock", "f2h_sdram0_clock";
> +
> + fpga-mgr = <&hps_0_fpgamgr>;
> + fpga-firmware = "soc_system.rbf";
> +
> + resets = <&hps_fpgabridge0 0>, <&hps_fpgabridge1 0>, <&hps_fpgabridge2 0>;
> + reset-names = "hps2fpga", "lwhps2fpga", "fpga2hps";
> +
> + gpio@0x100010040 {
> + compatible = "altr,pio-14.0", "altr,pio-1.0";
> + reg = <0x1 0x10040 0x20>;
> + clocks = <0x2>;
> + altr,gpio-bank-width = <0x4>;
> + resetvalue = <0x0>;
> + #gpio-cells = <0x2>;
> + gpio-controller;
> + };
> + };
> + };
> + };
> +};
> +

Just some quick thougths for the Socfpga case:

What you are describing here is a virtual bus, that is not existing on
at least the Socfpga, right? I don't like this.
You are mixing different independent busses/devices into one and I don't
see why. I see that this is just an example, but why
a) isn't the fpga-mgr the one knowing about the bitstream ?
You can't have two of these busses with different bitstreams anyway
And if you have multipe FPGAs you have multiple fpga-mgrs, no?
b) shouldn't the h2f/lwh2f/f2h bridges be the "simple-bus devices" instead of
just reset-controllers ? What about e.g. the bus width of the bridges?
It can change depending on the bitstream. When I have an IP core that does
DMA I might want my driver to be able to configure the bus width accordingly.
There are other settings in the bridges that I can not set when they are just
reset controllers.

I can understand that this is just an example, but again for the Socfpga case it
is IMHO wrong. I don't know about e.g. the Zynq without researching, though.

Regards,
Steffen

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