Re: fpga driver on custom PPC target platform (P4080) ...

On 11/07/2011 02:09 PM, Robert Sciuk wrote:

In my continuing saga of dev/tree driver development, I have a problem which might be obvious to those who have more experience in such matters.

I'm a bit perplexed on the tree nodes for the localbus/simplebus
nodes for my FPGA.  CS0 is reserved for booting (from NOR flash as
required by our design), CS1 is tied to an FPGA which will always be
present.  CS2 actually is tied to both of two (optional) fpga's,
which have been previously mapped by U-Boot (BRn/ORn configuration).
Should I specify a ranges command as follows?  This seems somehow
wrong, to me, and I'm wondering if there is an alternative
representation which would work better in this case.  If you recall,
the programming control lines are handled on the I2C bus, via a gpio
controller.  In an ideal world, the optional FPE1 and FPE2 fpgas will
have the identical .bts stream, and should support the option to
program both simultaneously, or each individually, but I'm at a loss
as how to best represent this in the tree.

If you need to poke an i2c bus to switch access between certain localbus
children, you should remove "simple-bus" from the compatible -- or
perhaps do something like:

localbus@ffe124000 {
	compatible = "fsl,p4080-elbc", "fsl,elbc", "simple-bus";
	...

	flash@0,0 {
		...
	};

	switched-bank@2,0 {
		// no simple-bus here
		compatible = "something specific to your board's setup";
		ranges = <0 0 2 0 0x8000>;

		// reg is here just to make the unit-addres valid
		reg = <2 0 0>;

		#address-cells = <2>;
		#size-cells = <1>;

		// specify a phandle to the i2c device and any other
		// relevant details for identifying which knob of the
		// switch needs to be turned...

		// replace x/y with appropriate switch ID, and 0 0x8000
		// with appropriate portion of the window being used by
		// each device
		fpga@x,0 {
			compatible = ...
			reg = <x 0 0x8000>;			
			...
		};

		fpga@y,0 {
			compatible = ...
			reg = <y 0 0x8000>;
			...
		};
	};
};

	        localbus@ffe124000 {
                compatible = "fsl,p4080-elbc", "fsl,elbc", "simple-bus";
                reg = <0xf 0xfe124000 0 0x1000>;
                interrupts = <25 2 0 0>;
                interrupt-parent = <&mpic>;
                #address-cells = <2>;
                #size-cells = <1>;

                /* Local bus region mappings */
                ranges = <0 0 0xf 0xe8000000 0x08000000         /* CS0: Boot flash */
                          1 0 0xf 0xd0000000 0x7fff             /* CS1: FPGA0 -  LIM */
                          2 0 0xf 0xd1000000 0x7fff             /* CS2: FPGA1 -  FPE1 */
                          2 0 0xf 0xd2000000 0x7fff >;          /* CS2: FPGA2 -  FPE2 */

The binding for FSL localbus nodes
(Documentation/devicetree/bindings/powerpc/fsl/lbc.txt) says that there
is a one-to-one correspondence between "ranges" entries and chipselects,
based on how the eLBC is actually programmed.  The details of what is
attached come in the subnodes.

I don't see how the above mapping is possible with eLBC -- you're
splitting CS2 among 0xd1000000..0xd1007fff and 0xd2000000..0xd2007fff.
Since you have CS1 at 0xd0000000, alignment restrictions prevent CS2
from covering both of those regions -- unless you've got overlapping
mappings, with CS2 being at least 0xd0000000..0xd3ffffff, and are
relying on CS1 taking priority due to being lower-numbered.

I hope you're not doing that, and that these aren't the real addresses
(or they can be changed) -- but if you must do this, that breaks the
one-to-one model, so you'd need both ranges entries.

Also note that the final cell in each ranges entry should be the size,
not the size minus one.

                fpe1: fpga@2, {
                }

                fpe2: fpga@2, {

This would be fine for a case where the devices are not switched, but
rather decode different addresses within the chipselect.

E.g. CS3 of arch/powerpc/boot/dts/socrates.dts

-Scott