3 files changed, 62 insertions, 0 deletions

diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX
index 9e642c5bf526..8dfc6708a257 100644
--- a/Documentation/00-INDEX
+++ b/Documentation/00-INDEX
@@ -232,6 +232,8 @@ memory.txt
         - info on typical Linux memory problems.
 mips/
         - directory with info about Linux on MIPS architecture.
+mmc/
+        - directory with info about the MMC subsystem
 mono.txt
         - how to execute Mono-based .NET binaries with the help of BINFMT_MISC.
 mutex-design.txt
diff --git a/Documentation/mmc/00-INDEX b/Documentation/mmc/00-INDEX
new file mode 100644
index 000000000000..fca586f5b853
--- /dev/null
+++ b/Documentation/mmc/00-INDEX
@@ -0,0 +1,4 @@
+00-INDEX
+        - this file
+mmc-dev-attrs.txt
+        - info on SD and MMC device attributes
diff --git a/Documentation/mmc/mmc-dev-attrs.txt b/Documentation/mmc/mmc-dev-attrs.txt
new file mode 100644
index 000000000000..ff2bd685bced
--- /dev/null
+++ b/Documentation/mmc/mmc-dev-attrs.txt
@@ -0,0 +1,56 @@
+SD and MMC Device Attributes
+============================
+
+All attributes are read-only.
+
+        cid                     Card Identifaction Register
+        csd                     Card Specific Data Register
+        scr                     SD Card Configuration Register (SD only)
+        date                    Manufacturing Date (from CID Register)
+        fwrev                   Firmware/Product Revision (from CID Register) (SD and MMCv1 only)
+        hwrev                   Hardware/Product Revision (from CID Register) (SD and MMCv1 only)
+        manfid                  Manufacturer ID (from CID Register)
+        name                    Product Name (from CID Register)
+        oemid                   OEM/Application ID (from CID Register)
+        serial                  Product Serial Number (from CID Register)
+        erase_size              Erase group size
+        preferred_erase_size    Preferred erase size
+
+Note on Erase Size and Preferred Erase Size:
+
+        "erase_size" is the  minimum size, in bytes, of an erase
+        operation.  For MMC, "erase_size" is the erase group size
+        reported by the card.  Note that "erase_size" does not apply
+        to trim or secure trim operations where the minimum size is
+        always one 512 byte sector.  For SD, "erase_size" is 512
+        if the card is block-addressed, 0 otherwise.
+
+        SD/MMC cards can erase an arbitrarily large area up to and
+        including the whole card.  When erasing a large area it may
+        be desirable to do it in smaller chunks for three reasons:
+                1. A single erase command will make all other I/O on
+                the card wait.  This is not a problem if the whole card
+                is being erased, but erasing one partition will make
+                I/O for another partition on the same card wait for the
+                duration of the erase - which could be a several
+                minutes.
+                2. To be able to inform the user of erase progress.
+                3. The erase timeout becomes too large to be very
+                useful.  Because the erase timeout contains a margin
+                which is multiplied by the size of the erase area,
+                the value can end up being several minutes for large
+                areas.
+
+        "erase_size" is not the most efficient unit to erase
+        (especially for SD where it is just one sector),
+        hence "preferred_erase_size" provides a good chunk
+        size for erasing large areas.
+
+        For MMC, "preferred_erase_size" is the high-capacity
+        erase size if a card specifies one, otherwise it is
+        based on the capacity of the card.
+
+        For SD, "preferred_erase_size" is the allocation unit
+        size specified by the card.
+
+        "preferred_erase_size" is in bytes.