Changes between Version 2 and Version 3 of MMC

Timestamp:

12/01/2017 04:34:36 PM (6 years ago)

Author:

Tim Harvey

Comment:

added eMMC details

MMC

@@ -3 +3 @@
 = !MultiMediaCard (MMC) =
 A !MultiMediaCard (MMC) is a memory card standard used for solid-state storage typically used in digital cameras, smart-phones, and portable media players. There are several form-factors of cards that fall under the specification. MMC cards use the SDIO data bus standard.
+
+
+[=#emmc]
+== Embedded Multi-Media Controller (eMMC) ==
+Embedded Multi-Media Controller (eMMC) refers to a package consisting of both flash memory and a flash memory controller integrated into a single on-board chip.
+
+eMMC is very similar to a microSD but differs in the following ways:
+ * supports several hardware partitions
+ * 8-bit data bus
+ * device is on-board and thus non removable
+
+Gateworks uses eMMC on several of its products:
+ * Newport:
+  - GW630x / GW640x: 8GiB (16MB BOOT0, 16MB BOOT1, 4MB RPMB, 7.09GiB USER)
+ * Ventana:
+  - GW560x: 8GiB 8GiB (16MB BOOT0, 16MB BOOT1, 4MB RPMB, 7.09GiB USER)
+
+
+[=#emmc-partitions]
+=== eMMC Partitions ===
+eMMC devices are partitioned into several hardware partitions but only one can be selected at a time:
+ - BOOT - one or more small partitions intended for boot firmware (eMMC 4.3 spec requires 2 boot and 1 user partition)
+ - RPMB - Replay Protected Memory Block - intended to store secure data (ie DRM content protection keys) (eMMC 4.4 spec adds the requirement of an RPMB partition)
+ - USER - a large partition intended for general storage
+
+Notes:
+ * BOOT and RPMB partitions are configured as SLC while USER can be SLC or MLC.
+ * Read / Write commands sent to an eMMC do not directly address the hardware partitions but instead a special command is used to select a partition.
+ * A Card Specific Data (CSD) register (EXT_CSD[179]) is used to configure what partition is selected at power-up. This can be configured within Linux via the {{{mmc-utils}}} application, or within U-Boot via the {{{mmc partconf}}} command (see below).
+ * It is up to the user to decide if and how to use each of the hardware partitions.
+
+Both Linux (see [#emmc-linux below]) and U-Boot (see [#emmc-uboot below]) support accessing the various partitions but in different ways.
+
+
+[=#emmc-partconf]
+=== eMMC PARTITION_CONFIG (Boot partition selection) ===
+Because eMMC provides multiple hardware partitions but only one can be selected at a time. A non-volatile register in the eMMC device provides a PARTITION_CONFIG that is used to determine what partition is selected at power-up for boot devices. To access this data you need to read/write a 'Card Specific Data' or CSD register (EXT_CSD[179] - EXT_CSC_PART_CONFIG). This can be done both in Linux (see [#emmc-linux below]) or U-Boot (see [#emmc-uboot below]).
+
+
+[=#emmc-uboot]
+=== U-Boot Support ===
+U-Boot provides access to eMMC devices through the {{{mmc}}} command and interface but adds an additional argument to the {{{mmc}}} interface to describe the hardware partition. The interface is therefore described as 'mmc <dev> <part>' where 'dev' is the mmc device (some boards have more than one) and 'part' is the hardware partition: 0=user, 1=boot0, 2=boot1.
+
+Use the {{{mmc dev}}} command to specify the device and partition:
+{{{#!bash
+mmc dev 0 0 # select user hw partition
+mmc dev 0 1 # select boot0 hw partition
+mmc dev 0 2 # select boot1 hw partition
+}}}
+
+If U-Boot has been built with {{{CONFIG_SUPPORT_EMMC_BOOT}}} some additional mmc commands are available:
+ * mmc bootbus <dev> <boot_bus_width> <reset_boot_bus_width> <boot_mode>
+ * mmc bootpart-resize <dev> <boot-part-size-mb> <rpmb-part-size-mb>
+ * mmc partconf <dev> <boot_ack> <boot-partition> <partition-access> # set PARTITION_CONFIG field
+ * mmc rst-function <dev> <value> # change RST_n_FUNCTION field between 0|1|2 (write-once)
+
+The {{{mmc partconf}}} command can be used to configure the PARTITION_CONFIG specifying what hardware partition to boot from:
+{{{#!bash
+mmc partconf 0 0 0 0 # disable boot partition (default unset condition; boots from user partition)
+mmc partconf 0 1 1 0 # set boot0 partition (with ack)
+mmc partconf 0 1 2 0 # set boot1 partition (with ack)
+mmc partconf 0 1 7 0 # set user partition (with ack)
+}}}
+
+If U-Boot has been built with {{{CONFIG_SUPPORT_EMMC_RPMB}}} the {{{mmc rpmb}}} command is available for reading, writing and programming the key for the Replay Protection Memory Block (RPMB) partition in eMMC.
+
+
+[=#emmc-linux]
+=== Linux Support ===
+Linux presents the various hardware partitions as separate devices:
+ - /dev/mmcblk0boot0 - BOOT0 partition
+ - /dev/mmcblk0boot1 - BOOT1 partition
+ - /dev/mmcblk0rpmb - RPMB partition
+ - /dev/mmcblk0 - USER partition
+
+Note that the BOOT partitions by default are read-only as they are typically used for sensitive boot firmware. To write to them you can disable {{{force_ro}}} in sysfs via:
+{{{#!bash
+echo 0 > /sys/class/block/mmcblk0boot0/force_ro
+}}}
+
+The Linux {{{mmc}}} application provides access to eMMC configuration through CSD registers. This open-source application is available at http://git.kernel.org/cgit/linux/kernel/git/cjb/mmc-utils.git/.
+ * To build it:
+{{{#!bash
+git clone git://git.kernel.org/pub/scm/linux/kernel/git/cjb/mmc-utils.git
+cd mmc-utils
+make
+}}}
+ * Alternatively you can install this from a pre-built deb:
+  * Newport (arm64):
+{{{#!bash
+wget http://dev.gateworks.com/images/mmc-utils_0~gita3d3331-3~armbian5.35+1_arm64.deb
+dpkg -i mmc-utils_0~gita3d3331-3~armbian5.35+1_arm64.deb
+}}}
+ * Ventana (armhf):
+{{{#!bash
+wget http://dev.gateworks.com/images/mmc-utils_0~gita3d3331-3~armbian5.35+1_armhf.deb
+dpkg -i mmc-utils_0~gita3d3331-3~armbian5.35+1_armhf.deb
+}}}
+
+You can use the {{{mmc}}} utility to configure the eMMC PARTITION_CONFIG to specify the boot device on power-up via {{{mmc bootpart enable <boot_partition> <send_ack> <device>}}} where boot_partition specifies the hardware partition (1=boot0, 2=boot1, 7=user), send_ack specifies the device must send an awknoledgement (for fast boot), and device is the root mmc block device of the eMMC:
+{{{#!bash
+# set boot partition to boot0
+mmc bootpart enable 1 0 /dev/mmcblk0
+# set boot partition to boot1
+mmc bootpart enable 2 0 /dev/mmcblk0
+# set boot partition to user
+mmc bootpart enable 7 0 /dev/mmcblk0
+}}}
+
+Some additional use cases:
+{{{#!bash
+# show PARTITION_CONFIG:
+mmc extcsd read /dev/mmcblk0 | grep PARTITION_CONFIG
+# show BUS CONFIG:
+mmc extcsd read /dev/mmcblk0 | grep BOOT_BUS_CONDITIONS
+# disable boot partition
+mmc bootpart enable 0 0 /dev/mmcblk0
+}}}
+
+References:
+ * https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/mmc/mmc-tools.txt