On 08/24/2012 01:10 PM, Timur Tabi wrote:

Add support for an MDIO bus multiplexer controlled by a simple memory-mapped
device, like an FPGA.  The device must be memory-mapped and contain only
8-bit registers (which keeps things simple).

Tested on a Freescale P5020DS board which uses the "PIXIS" FPGA attached
to the localbus.

+Properties for an MDIO bus multiplexer controlled by a memory-mapped device
+
+This is a special case of a MDIO bus multiplexer.  A memory-mapped device,
+like an FPGA, is used to control which child bus is connected.  The mdio-mux
+node must be a child of the memory-mapped device.  The driver currently only
+supports devices with eight-bit registers.

That last sentence seems like a property of the driver, not the binding;
I could easily anticipate allowing the size to be 1 or 2 or 4, and a
driver adapter to that in the future.

Otherwise, this binding looks great now.

+static int mdio_mux_mmioreg_switch_fn(int current_child, int desired_child,
+				      void *data)
+{
+	struct mdio_mux_mmioreg_state *s = data;
+
+	if (current_child ^ desired_child) {
+		void *p = ioremap(s->phys, 1);
+		uint8_t x, y;
+
+		if (!p)
+			return -ENOMEM;

Why not map it during probe?

+		x = ioread8(p);
+		y = (x & ~s->mask) | desired_child;
+		if (x != y) {

Isn't that always true, given if (current_child ^ desired_child) above?

+			iowrite8((x & ~s->mask) | desired_child, p);
+			pr_debug("%s: %02x -> %02x\n", __func__, x, y);
+		}
+
+		iounmap(p);
+	}
+
+	return 0;
+}