| # SDMMC drivers architecture |
| |
| The SDMMC driver stack is divided into two main components: platform drivers |
| that talk directly to controller hardware, and the core driver that handles |
| protocol-specific device initialization and communication. The core driver is |
| further divided into an SDIO driver and a block driver (for SD and eMMC). Each |
| SDMMC controller has a different platform driver, while the core driver is |
| used on all platforms. |
| |
| ## Bringup |
| |
| Bringing up an SoC with a new SDMMC controller requires writing a new platform |
| driver. If the controller implements the SDHCI specification then this driver |
| should implement |
| [fuchsia.hardware.sdhci](/sdk/banjo/fuchsia.hardware.sdhci/sdhci.banjo), otherwise it |
| should implement |
| [fuchsia.hardware.sdmmc](/sdk/banjo/fuchsia.hardware.sdmmc/sdmmc.banjo). It may be |
| helpful to disable DMA and higher speed modes through `SdmmcHostInfo` and |
| `SdmmcHostPrefs` until the basic functionality of the hardware has been |
| validated. See the SDHCI and SDMMC protocol definitions for more information. |
| |
| ## SD/eMMC core driver |
| |
| The SD/eMMC block driver creates a device that implements |
| [fuchsia.hardware.block.BlockImpl](/sdk/banjo/fuchsia.hardware.block/block.banjo) and |
| [fuchsia.hardware.block.partition](/sdk/banjo/fuchsia.hardware.block.partition/partition.banjo) |
| for the user data partition, as well as devices for the boot0 and boot1 |
| partitions if enabled (eMMC only). A device implementing |
| [fuchsia.hardware.rpmb](/sdk/banjo/fuchsia.hardware.rpmb/rpmb.banjo) is created if the |
| device supports it (eMMC only, based on JEDEC standard JESD84-B51 section 6.6.22). |
| |
| ## SDIO core driver |
| |
| The SDIO core driver creates devices that implement |
| [fuchsia.hardware.sdio](/sdk/banjo/fuchsia.hardware.sdio/sdio.banjo), one for |
| each IO function. Whereas the only expected client of the SD/eMMC block driver |
| is the storage stack, the SDIO driver will have different clients depending on |
| what kind of SDIO card is detected. Client drivers bind to the SDIO core driver |
| using the bind variables specified in the table below. Client drivers that use |
| more than one IO function should bind to a composite device that has each |
| function device as a fragment. Note that there could be multiple concurrent SDIO |
| client drivers for combo cards, e.g. for Bluetooth and WiFi, in which case |
| access to the bus will be shared through the core driver. Clients also cannot |
| directly access function 0 to prevent possibly disrupting other clients. See the |
| SDIO protocol definition for more information. |
| |
| ### SDIO client binding |
| |
| | Bind variable | Meaning | |
| | ---------------------| ------------------------------------------------------| |
| | `BIND_SDIO_VID` | The IO function's manufacturer ID read from FBR | |
| | `BIND_SDIO_PID` | The IO function's product ID read from FBR | |
| | `BIND_SDIO_FUNCTION` | The IO function number from 1 to 7 | |
| |
| ## Device diagram |
| |
|  |
