RFC: book3e: DCR MMIO for IBM Blue Gene/Q

Jimi Xenidis jimix at pobox.com
Mon Nov 5 03:32:43 EST 2012

I want to use the stuff in arch/platform/sysdev/dcr.c and I have a couple of questions:
1) anyone have a good devtree binding for this?
I'm thinking:
	bgq {
		#address-cells = <2>;
		#size-cells = <2>;

		dcr {
			reg = <0x3ff 0xe0000000 0x0 0x08000000>;
			compatible = "ibm,bgq-dcr";
			dcr-access-method = "mmio";
			dcr-mmio-stride = <??>;

I'm not sure what stride I will use since I have yet to figure out the DCR numbering in play at the moment, which will be painful.
Also, some clarity to the following would be nice:
	/* Stride is not properly defined yet, default to 0x10 for Axon */
	p = of_get_property(dp, "dcr-mmio-stride", NULL);
	stride = (p == NULL) ? 0x10 : *p;

	/* XXX FIXME: Which property name is to use of the 2 following ? */
	p = of_get_property(dp, "dcr-mmio-range", NULL);
	if (p == NULL)
		p = of_get_property(dp, "dcr-mmio-space", NULL);
	if (p == NULL)
		goto done;

I guess my "reg" property is not useful to the code?
Is there a preference over dcr-mmio-range/space or in the absence of these to we should use "reg"?

2) I need 64 bit reads and writes
My intention is to have dcr_{read,write}_generic_{mmio,native} take an unsigned long for value all the way down.
For the native case, this would make is similar to mtspr and mfspr.
For the MMIO case, the selected in/out size would be based on "#ifdef __powerpc64__"



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