diff --git a/Documentation/devicetree/bindings/mailbox/nvidia,tegra186-hsp.txt b/Documentation/devicetree/bindings/mailbox/nvidia,tegra186-hsp.txt
index b99d25fc2f26e7a2bd6a4548f0b7a8f9baae8723..ff3eafc5a882bca7cf04c581401fe36b5785277c 100644
--- a/Documentation/devicetree/bindings/mailbox/nvidia,tegra186-hsp.txt
+++ b/Documentation/devicetree/bindings/mailbox/nvidia,tegra186-hsp.txt
@@ -15,12 +15,15 @@ Required properties:
     Array of strings.
     one of:
     - "nvidia,tegra186-hsp"
+    - "nvidia,tegra194-hsp", "nvidia,tegra186-hsp"
 - reg : Offset and length of the register set for the device.
 - interrupt-names
     Array of strings.
     Contains a list of names for the interrupts described by the interrupt
     property. May contain the following entries, in any order:
     - "doorbell"
+    - "sharedN", where 'N' is a number from zero up to the number of
+      external interrupts supported by the HSP instance minus one.
     Users of this binding MUST look up entries in the interrupt property
     by name, using this interrupt-names property to do so.
 - interrupts
@@ -29,12 +32,29 @@ Required properties:
     in a matching order.
 - #mbox-cells : Should be 2.
 
-The mbox specifier of the "mboxes" property in the client node should
-contain two data. The first one should be the HSP type and the second
-one should be the ID that the client is going to use. Those information
-can be found in the following file.
+The mbox specifier of the "mboxes" property in the client node should contain
+two cells. The first cell determines the HSP type and the second cell is used
+to identify the mailbox that the client is going to use.
 
-- <dt-bindings/mailbox/tegra186-hsp.h>.
+For doorbells, the second cell specifies the index of the doorbell to use.
+
+For shared mailboxes, the second cell is composed of two fields:
+- bits 31..24:
+    A bit mask of flags that further specify how the shared mailbox will be
+    used. Valid flags are:
+    - bit 31:
+        Defines the direction of the mailbox. If set, the mailbox will be used
+        as a producer (i.e. used to send data). If cleared, the mailbox is the
+        consumer of data sent by a producer.
+
+- bits 23.. 0:
+    The index of the shared mailbox to use. The number of available mailboxes
+    may vary by instance of the HSP block and SoC generation.
+
+The following file contains definitions that can be used to construct mailbox
+specifiers:
+
+    <dt-bindings/mailbox/tegra186-hsp.h>
 
 Example:
 
diff --git a/include/dt-bindings/mailbox/tegra186-hsp.h b/include/dt-bindings/mailbox/tegra186-hsp.h
index bcab5b7ca7852c2f157fbfe4d98983e9e5f9ac2c..3bdec7a84d35cfd98c2d203aff7b11792ca3e4f4 100644
--- a/include/dt-bindings/mailbox/tegra186-hsp.h
+++ b/include/dt-bindings/mailbox/tegra186-hsp.h
@@ -22,4 +22,15 @@
 #define TEGRA_HSP_DB_MASTER_CCPLEX 17
 #define TEGRA_HSP_DB_MASTER_BPMP 19
 
+/*
+ * Shared mailboxes are unidirectional, so the direction needs to be specified
+ * in the device tree.
+ */
+#define TEGRA_HSP_SM_MASK 0x00ffffff
+#define TEGRA_HSP_SM_FLAG_RX (0 << 31)
+#define TEGRA_HSP_SM_FLAG_TX (1 << 31)
+
+#define TEGRA_HSP_SM_RX(x) (TEGRA_HSP_SM_FLAG_RX | ((x) & TEGRA_HSP_SM_MASK))
+#define TEGRA_HSP_SM_TX(x) (TEGRA_HSP_SM_FLAG_TX | ((x) & TEGRA_HSP_SM_MASK))
+
 #endif