usb: ulpi: Support device discovery via DT

The qcom HSIC ULPI phy doesn't have any bits set in the vendor or
product ID registers. This makes it impossible to make a ULPI
driver match against the ID registers. Add support to discover
the ULPI phys via DT help alleviate this problem. In the DT case,
we'll look for a ULPI bus node underneath the device registering
the ULPI viewport (or the parent of that device to support
chipidea's device layout) and then match up the phy node
underneath that with the ULPI device that's created.

The side benefit of this is that we can use standard properties
in the phy node like clks, regulators, gpios, etc. because we
don't have firmware like ACPI to turn these things on for us. And
we can use the DT phy binding to point our phy consumer to the
phy provider.

The ULPI bus code supports native enumeration by reading the
vendor ID and product ID registers at device creation time, but
we can't be certain that those register reads will succeed if the
phy is not powered up. To avoid any problems with reading the ID
registers before the phy is powered we fallback to DT matching
when the ID reads fail.

If the ULPI spec had some generic power sequencing for these
registers we could put that into the ULPI bus layer and power up
the device before reading the ID registers. Unfortunately this
doesn't exist and the power sequence is usually device specific.
By having the device matched up with DT we can avoid this
problem.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: <devicetree@vger.kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: Peter Chen <peter.chen@nxp.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/usb/ulpi.txt b/Documentation/devicetree/bindings/usb/ulpi.txt
new file mode 100644
index 000000000000..ca179dc4bd50
--- /dev/null
+++ b/Documentation/devicetree/bindings/usb/ulpi.txt
@@ -0,0 +1,20 @@
+ULPI bus binding
+----------------
+
+Phys that are behind a ULPI connection can be described with the following
+binding. The host controller shall have a "ulpi" named node as a child, and
+that node shall have one enabled node underneath it representing the ulpi
+device on the bus.
+
+EXAMPLE
+-------
+
+usb {
+	compatible = "vendor,usb-controller";
+
+	ulpi {
+		phy {
+			compatible = "vendor,phy";
+		};
+	};
+};