diff --git a/doc/usage/cmd/mmc.rst b/doc/usage/cmd/mmc.rst
index 71a0303..c0924ba 100644
--- a/doc/usage/cmd/mmc.rst
+++ b/doc/usage/cmd/mmc.rst
@@ -21,6 +21,7 @@
     mmc bootpart-resize <dev> <dev part size MB> <RPMB part size MB>
     mmc partconf <dev> [[varname] | [<boot_ack> <boot_partition> <partition_access>]]
     mmc rst-function <dev> <value>
+    mmc reg read <reg> <offset> [env]
 
 Description
 -----------
@@ -183,6 +184,31 @@
         0x3
             Reserved
 
+The 'mmc reg read <reg> <offset> [env]' reads eMMC card register and
+either print it to standard output, or store the value in environment
+variable.
+
+<reg> with
+optional offset <offset> into the register array, and print it to
+standard output or store it into environment variable [env].
+
+    reg
+        cid
+            The Device IDentification (CID) register. Uses offset.
+        csd
+            The Device-Specific Data (CSD) register. Uses offset.
+        dsr
+            The driver stage register (DSR).
+        ocr
+            The operation conditions register (OCR).
+        rca
+            The relative Device address (RCA) register.
+        extcsd
+            The Extended CSD register. Uses offset.
+    offset
+        For 'cid'/'csd' 128 bit registers '[0..3]' in 32-bit increments. For 'extcsd' 512 bit register '[0..512,all]' in 8-bit increments, or 'all' to read the entire register.
+    env
+        Optional environment variable into which 32-bit value read from register should be stored.
 
 Examples
 --------