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diff --git a/Documentation/mmc/mmc-dev-attrs.txt b/Documentation/mmc/mmc-dev-attrs.txt
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+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.