mmc: Add support for marking hpi as broken through devicetree

The eMMC on a tablet I've will stop working / communicating as soon as
the kernel executes:

		mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
 				EXT_CSD_HPI_MGMT, 1,
 				card->ext_csd.generic_cmd6_time);

There seems to be no way to reliable identify eMMC-s which have a broken
hpi implementation, but at least for eMMC's which are soldered onto a board
we can work around this by specifying that hpi is broken in devicetree.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/mmc/mmc-card.txt b/Documentation/devicetree/bindings/mmc/mmc-card.txt
new file mode 100644
index 000000000000..a70fcd65b9ea
--- /dev/null
+++ b/Documentation/devicetree/bindings/mmc/mmc-card.txt
@@ -0,0 +1,31 @@
+mmc-card / eMMC bindings
+------------------------
+
+This documents describes the devicetree bindings for a mmc-host controller
+child node describing a mmc-card / an eMMC, see "Use of Function subnodes"
+in mmc.txt
+
+Required properties:
+-compatible : Must be "mmc-card"
+-reg        : Must be <0>
+
+Optional properties:
+-broken-hpi : Use this to indicate that the mmc-card has a broken hpi
+              implementation, and that hpi should not be used
+
+Example:
+
+&mmc2 {
+	pinctrl-names = "default";
+	pinctrl-0 = <&mmc2_pins_a>;
+	vmmc-supply = <&reg_vcc3v3>;
+	bus-width = <8>;
+	non-removable;
+	status = "okay";
+
+	mmccard: mmccard@0 {
+		reg = <0>;
+		compatible = "mmc-card";
+		broken-hpi;
+	};
+};