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AM335x MMC/SD Driver's Guide
AM335x has 3 instances MMC/SD/SDIO host controller, which provides an interface between microprocessor and either MMC, SD memory cards, or SDIO cards. The current version of the user guide talks about the MMC/SD controller.
The MMC/SD driver is implemented as a block driver on top of host controller as a HSMMC controller driver and supports SD, SD High Speed and SDHC cards. This driver only supports for 4 bit modes(no SPI mode, 1/8 Bit). Both DMA & polled mode of data transfer is supported.
Acronyms & Definitions
|HS-MMC||High Speed MMC|
|SDHC||SD High Capacity|
The default kernel configuration enables support for MMC/SD(built-in to kernel). OMAP MMC/SD driver is reused for AM335x.
The selection of MMC/SD/SDIO driver can be modified as follows: start Linux Kernel Configuration tool.
$ make CROSS_COMPILE=arm-arago-linux-gnueabi- ARCH=arm menuconfig
- Select Device Drivers from the main menu.
... ... Kernel Features ---> Boot options ---> CPU Power Management ---> Floating point emulation ---> Userspace binary formats ---> Power management options ---> [*] Networking support ---> Device Drivers ---> ... ...
Building into Kernel 
- Select MMC/SD/SDIO card support from the menu.
... ... [*] USB support ---> <*> MMC/SD/SDIO card support ---> < > Sony MemoryStick card support (EXPERIMENTAL) ---> ... ...
- Select OMAP HS MMC driver
[ ] MMC debugging [*] Assume MMC/SD cards are non-removable (DANGEROUS) [ ] MMC host clock gating (EXPERIMENTAL) *** MMC/SD/SDIO Card Drivers *** <*> MMC block device driver (8) Number of minors per block device [*] Use bounce buffer for simple hosts <*> SDIO UART/GPS class support < > MMC host test driver ... < > TI OMAP Multimedia Card Interface support <*> TI OMAP High Speed Multimedia Card Interface support ...
Building as Loadable Kernel Module
- To build the above components as modules, press 'M' key on every config entries shown below to build them as module:
<M> MMC/SD/SDIO card support ---> <M> MMC block device driver <M> TI OMAP High Speed Multimedia Card Interface support
- After doing module selection, exit and save the kernel configuration when prompted.
- Now build the kernel and modules form Linux build host as
$ make CROSS_COMPILE=arm-arago-linux-gnueabi- ARCH=arm uImage $ make CROSS_COMPILE=arm-arago-linux-gnueabi- ARCH=arm modules
- Following modules will be built
mmc_core.ko mmc_block.ko omap_hsmmc.ko
- Boot the newly built kernel and transfer the above mentioned .ko files to the filesystem
- Navigate to the directory containing these modules and insert them form type the following commands in console to insert the modules in specified order:
# insmod mmc_core.ko # insmod mmc_block.ko # insmod omap_hsmmc.ko
- If 'udev' is running and the SD card is already inserted, the devices nodes will be created and filesystem will be automatically mounted if exists on the card. Block device nodes(such as /dev/mmcblockp1, /dev/mmcblockp2) are created for user space access.