docs: Add eMMC device model description

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <b9c3ff21e7170fef5d0e7d08698a113d2a64e649.1762261430.git.jan.kiszka@siemens.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

diff --git a/docs/system/device-emulation.rst b/docs/system/device-emulation.rst
index db714ad47aa5bf91f6bd73a522cb8774c70c8e10..971325527a1577a8044bfc8f8224326945a32345 100644 (file)
--- a/docs/system/device-emulation.rst
+++ b/docs/system/device-emulation.rst
@@ -88,6 +88,7 @@ Emulated Devices
    devices/canokey.rst
    devices/ccid.rst
    devices/cxl.rst
+   devices/emmc.rst
    devices/igb.rst
    devices/ivshmem-flat.rst
    devices/ivshmem.rst

diff --git a/docs/system/devices/emmc.rst b/docs/system/devices/emmc.rst
new file mode 100644 (file)
index 0000000..e62adfd
--- /dev/null
+++ b/docs/system/devices/emmc.rst
@@ -0,0 +1,55 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+==============
+eMMC Emulation
+==============
+
+Besides SD card emulation, QEMU also offers an eMMC model as found on many
+embedded boards. An eMMC, just like an SD card, is connected to the machine
+via an SDHCI controller.
+
+Create eMMC Images
+==================
+
+A recent eMMC consists of 4 partitions: 2 boot partitions, 1 Replay protected
+Memory Block (RPMB), and the user data area. QEMU expects backing images for
+the eMMC to contain those partitions concatenated in exactly that order.
+However, the boot partitions as well as the RPMB might be absent if their sizes
+are configured to zero.
+
+The eMMC specification defines alignment constraints for the partitions. The
+two boot partitions must be of the same size. Furthermore, boot and RPMB
+partitions must be multiples of 128 KB with a maximum of 32640 KB for each
+boot partition and 16384K for the RPMB partition.
+
+The alignment constrain of the user data area depends on its size. Up to 2
+GByte, the size must be a power of 2. From 2 GByte onward, the size has to be
+multiples of 512 byte.
+
+QEMU is enforcing those alignment rules before instantiating the device.
+Therefore, the provided image has to strictly follow them as well. The helper
+script ``scripts/mkemmc.sh`` can be used to create compliant images, with or
+without pre-filled partitions. E.g., to create an eMMC image from a firmware
+image and an OS image with an empty 2 MByte RPMB, use the following command:
+
+.. code-block:: console
+
+    scripts/mkemmc.sh -b firmware.img -r /dev/zero:2M os.img emmc.img
+
+This will take care of rounding up the partition sizes to the next valid value
+and will leave the RPMB and the second boot partition empty (zeroed).
+
+Adding eMMC Devices
+===================
+
+An eMMC is either automatically created by a machine model (e.g. Aspeed boards)
+or can be user-created when using a PCI-attached SDHCI controller. To
+instantiate the eMMC image from the example above in a machine without other
+SDHCI controllers while assuming that the firmware needs a boot partitions of
+1 MB, use the following options:
+
+.. code-block:: console
+
+    -drive file=emmc.img,if=none,format=raw,id=emmc-img
+    -device sdhci-pci
+    -device emmc,drive=emmc-img,boot-partition-size=1048576,rpmb-partition-size=2097152