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L4Re Operating System Framework
Interface and Usage Documentation
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L4Re Operating System Framework
Interface and Usage Documentation
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The eMMC driver is a driver for PCI Express eMMC controllers.
The eMMC driver can be started with Lua like this:
local emmc_bus = L4.default_loader:new_channel();
L4.default_loader:start({
caps = {
vbus = vbus_emmc,
svr = emmc_bus:svr(),
},
},
"rom/emmc-drv");
First, an IPC gate (emmc_bus) is created which is used between the eMMC driver and a client to request access to a particular disk or partition. The server side is assigned to the mandatory svr capability of the eMMC driver. See the sector below on how to configure access to a disk or partition.
The eMMC driver needs access to a virtual bus capability (vbus). On the virtual bus the eMMC driver searches for eMMC compliant storage controllers. Please see io's documentation about how to setup a virtual bus.
The eMMC driver supports SDHCI and SDHI controllers, in particular
doc/pcie-ecam.io),doc/qemu-patch.diff).In the example above the eMMC driver is started in its default configuration. To customize the configuration of the eMMC driver it accepts the following command line options:
-v
Enable verbose mode. You can repeat this option up to three times to increase verbosity up to trace level.
-q
This option enables the quiet mode. All output is silenced.
--disable-mode <mode>
This option allows to disable certain eMMC/SD card modes from autodetection. The modes hs26, hs52, hs52_ddr, hs200, and hs400 are determined for eMMC devices. The modes sdr12, sdr25, sdr50, sdr104, ddr50 are determined for SD card devices. This option can be specified multiple times to disable multiple modes.
--max-seg <number>
Maximum number of segments per request. This number is announced to the virtio interface and is also relevant for the required bounce buffer size, see below. Default is 64.
--client <cap_name>
This option starts a new static client option context. The following device, ds-max, readonly and dma-map-all options belong to this context until a new client option context is created.
The option parameter is the name of a local IPC gate capability with server rights.
--device <UUID>
This option denotes the partition UUID of the partition to be exported for the client specified in the preceding client option.
--ds-max <max>
This option sets the upper limit of the number of dataspaces the client is able to register with the eMMC driver for virtio DMA.
--readonly
This option sets the access to disks or partitions to read only for the preceding client option.
--dma-map-all
Map the entire client dataspace into the DMA space at the first I/O request and never unmap the dataspace until the client is destroyed. The default behavior is to map the relevant part of the dataspace before an I/O request and unmap it after the request.
Prior to connecting a client to a virtual block session it has to be created using the following Lua function. It has to be called on the client side of the IPC gate capability whose server side is bound to the eMMC driver.
create(obj_type, "device=<UUID>", "ds-max=<max>")
obj_type
The type of object that should be created by the driver. The type must be a positive integer. Currently the following objects are supported:
0: Virtio block host"device=<UUID>"
This string denotes a partition UUID the client wants to be exported via the Virtio block interface.
"ds-max=<max>"
Specifies the upper limit of the number of dataspaces the client is allowed to register with the eMMC driver for virtio DMA.
"readonly"
This option sets the access to disks or partitions to read only for this client connection.
"dma-map-all"
Map the entire client dataspace into the DMA space at the first I/O request and never unmap the dataspace until the client is destroyed. The default behavior is to map the relevant part of the dataspace before an I/O request and unmap it after the request.
If the create() call is successful a new capability which references an eMMC virtio driver is returned. A client uses this capability to communicate with the eMMC driver using the Virtio block protocol.
The driver makes use of certain capabilities:
vbus
Required for finding the device which should be driven by this driver.
bbds
Only used by the SDHCI driver.
Certain SDHCI devices cannot handle DMA requests with DMA buffers beyond 4GiB. The provided dataspace is used as bounce buffer if the driver detects that a certain request needs it.
Note: The bounce buffer needs to be able to hold the memory for an entire read/write request. That means that the buffer is divided into the number of maximum segments (see --max-seg parameter). Note: The physical memory of the provided dataspace must be contiguous.
sdhci_adma_buf
Only used by the SDHCI driver.
Page (4096 bytes) for storing DMA descriptors for the SDHCI driver. If this capability is not provided, the driver will allocate an arbitrary page.
bcm2835_mbox_mem
Only used by the SDHCI driver when attaching to an bcm2711-compatible device.
Page (4096 bytes) for storing bcm2835 mbox messages. The firmware mbox is used to perform voltage switching for certain SD card configurations. If this capability is not provided, the driver will allocate an arbitrary page.
A couple of examples on how to request different disks or partitions are listed below.
vda1 = emmc_bus:create(0, "ds-max=5", "device=AFFA05B0-9379-480E-B9C6-5FF57FB1D194")
emmc_cl1 capability to communicate with the eMMC driver. local emmc_cl1 = L4.default_loader:new_channel();
local emmc_bus = L4.default_loader:new_channel();
L4.default_loader:start({
caps = {
vbus = vbus_emmc,
svr = emmc_bus:svr(),
cl1 = emmc_cl1:svr(),
},
},
"rom/emmc-drv --client cl1 --device 88E59675-4DC8-469A-98E4-B7B021DC7FBE --ds-max 5");
Accessing a device from QEMU:
The file pcie-ecam.io contains an IO config file which is able to use the QEMU PCI controller to search for attached eMMC devices.
eMMC emulation with QEMU:
The attached patch extends QEMU SD card emulation to emulate eMMC devices. After applying the patch and recompiling QEMU, attach the following parameters to your QEMU command line (assuming that $HOME/foobar.img is the eMMC medium):
1.9.8