--- /dev/null
+The U-Boot Driver Model Project
+===============================
+MMC system analysis
+===================
+Marek Vasut <marek.vasut@gmail.com>
+2012-02-25
+
+I) Overview
+-----------
+
+The MMC subsystem is already quite dynamic in it's nature. It's only necessary
+to flip the subsystem to properly defined API.
+
+The probing process of MMC drivers start by calling "mmc_initialize()",
+implemented by MMC framework, from the architecture initialization file. The
+"mmc_initialize()" function in turn calls "board_mmc_init()" function and if
+this doesn't succeed, "cpu_mmc_init()" function is called. It is important to
+note that both of the "*_mmc_init()" functions have weak aliases to functions
+which automatically fail.
+
+Both of the "*_mmc_init()" functions though serve only one purpose. To call
+driver specific probe function, which in turn actually registers the driver with
+MMC subsystem. Each of the driver specific probe functions is currently done in
+very ad-hoc manner.
+
+The registration with the MMC subsystem is done by calling "mmc_register()",
+whose argument is a runtime configured structure of information about the MMC
+driver. Currently, the information structure is intermixed with driver's internal
+data. The description of the structure follows:
+
+struct mmc {
+ /*
+ * API: Allows this driver to be a member of the linked list of all MMC drivers
+ * registered with MMC subsystem
+ */
+ struct list_head link;
+
+ /* DRIVER: Name of the registered driver */
+ char name[32];
+
+ /* DRIVER: Driver's private data */
+ void *priv;
+
+ /* DRIVER: Voltages the host bus can provide */
+ uint voltages;
+
+ /* API: Version of the card */
+ uint version;
+
+ /* API: Test if the driver was already initialized */
+ uint has_init;
+
+ /* DRIVER: Minimum frequency the host bus can provide */
+ uint f_min;
+
+ /* DRIVER: Maximum frequency the host bus can provide */
+ uint f_max;
+
+ /* API: Is the card SDHC */
+ int high_capacity;
+
+ /* API: Actual width of the bus used by the current card */
+ uint bus_width;
+
+ /*
+ * DRIVER: Clock frequency to be configured on the host bus, this is read-only
+ * for the driver.
+ */
+ uint clock;
+
+ /* API: Capabilities of the card */
+ uint card_caps;
+
+ /* DRIVER: MMC bus capabilities */
+ uint host_caps;
+
+ /* API: Configuration and ID data retrieved from the card */
+ uint ocr;
+ uint scr[2];
+ uint csd[4];
+ uint cid[4];
+ ushort rca;
+
+ /* API: Partition configuration */
+ char part_config;
+
+ /* API: Number of partitions */
+ char part_num;
+
+ /* API: Transmission speed */
+ uint tran_speed;
+
+ /* API: Read block length */
+ uint read_bl_len;
+
+ /* API: Write block length */
+ uint write_bl_len;
+
+ /* API: Erase group size */
+ uint erase_grp_size;
+
+ /* API: Capacity of the card */
+ u64 capacity;
+
+ /* API: Descriptor of this block device */
+ block_dev_desc_t block_dev;
+
+ /* DRIVER: Function used to submit command to the card */
+ int (*send_cmd)(struct mmc *mmc,
+ struct mmc_cmd *cmd, struct mmc_data *data);
+
+ /* DRIVER: Function used to configure the host */
+ void (*set_ios)(struct mmc *mmc);
+
+ /* DRIVER: Function used to initialize the host */
+ int (*init)(struct mmc *mmc);
+
+ /* DRIVER: Function used to report the status of Card Detect pin */
+ int (*getcd)(struct mmc *mmc);
+
+ /*
+ * DRIVER: Maximum amount of blocks sent during multiblock xfer,
+ * set to 0 to autodetect.
+ */
+ uint b_max;
+};
+
+The API above is the new API used by most of the drivers. There're still drivers
+in the tree that use old, legacy API though.
+
+2) Approach
+-----------
+
+To convert the MMC subsystem to a proper driver model, the "struct mmc"
+structure will have to be properly split in the first place. The result will
+consist of multiple parts, first will be the structure defining operations
+provided by the MMC driver:
+
+struct mmc_driver_ops {
+ /* Function used to submit command to the card */
+ int (*send_cmd)(struct mmc *mmc,
+ struct mmc_cmd *cmd, struct mmc_data *data);
+ /* DRIVER: Function used to configure the host */
+ void (*set_ios)(struct mmc *mmc);
+ /* Function used to initialize the host */
+ int (*init)(struct mmc *mmc);
+ /* Function used to report the status of Card Detect pin */
+ int (*getcd)(struct mmc *mmc);
+}
+
+The second part will define the parameters of the MMC driver:
+
+struct mmc_driver_params {
+ /* Voltages the host bus can provide */
+ uint32_t voltages;
+ /* Minimum frequency the host bus can provide */
+ uint32_t f_min;
+ /* Maximum frequency the host bus can provide */
+ uint32_t f_max;
+ /* MMC bus capabilities */
+ uint32_t host_caps;
+ /*
+ * Maximum amount of blocks sent during multiblock xfer,
+ * set to 0 to autodetect.
+ */
+ uint32_t b_max;
+}
+
+And finally, the internal per-card data of the MMC subsystem core:
+
+struct mmc_card_props {
+ /* Version of the card */
+ uint32_t version;
+ /* Test if the driver was already initializes */
+ bool has_init;
+ /* Is the card SDHC */
+ bool high_capacity;
+ /* Actual width of the bus used by the current card */
+ uint8_t bus_width;
+ /* Capabilities of the card */
+ uint32_t card_caps;
+ /* Configuration and ID data retrieved from the card */
+ uint32_t ocr;
+ uint32_t scr[2];
+ uint32_t csd[4];
+ uint32_t cid[4];
+ uint16_t rca;
+ /* Partition configuration */
+ uint8_t part_config;
+ /* Number of partitions */
+ uint8_t part_num;
+ /* Transmission speed */
+ uint32_t tran_speed;
+ /* Read block length */
+ uint32_t read_bl_len;
+ /* Write block length */
+ uint32_t write_bl_len;
+ /* Erase group size */
+ uint32_t erase_grp_size;
+ /* Capacity of the card */
+ uint64_t capacity;
+ /* Descriptor of this block device */
+ block_dev_desc_t block_dev;
+}
+
+The probe() function will then register the MMC driver by calling:
+
+ mmc_device_register(struct instance *i, struct mmc_driver_ops *o,
+ struct mmc_driver_params *p);
+
+The struct mmc_driver_params will have to be dynamic in some cases, but the
+driver shouldn't modify it's contents elsewhere than in probe() call.
+
+Next, since the MMC drivers will now be consistently registered into the driver
+tree from board file, the functions "board_mmc_init()" and "cpu_mmc_init()" will
+disappear altogether.
+
+As for the legacy drivers, these will either be converted or removed altogether.
+
+III) Analysis of in-tree drivers
+--------------------------------
+
+ 1) arm_pl180_mmci.c
+ -------------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
+
+ 2) atmel_mci.c
+ --------------
+ This driver uses the legacy API and should be removed unless converted. It is
+ probably possbible to replace this driver with gen_atmel_mci.c . No conversion
+ will be done on this driver.
+
+ 3) bfin_sdh.c
+ -------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
+
+ 4) davinci_mmc.c
+ ----------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
+
+ 5) fsl_esdhc.c
+ --------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple, unless some problem appears due to the FDT
+ component of the driver.
+
+ 6) ftsdc010_esdhc.c
+ -------------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
+
+ 7) gen_atmel_mci.c
+ ------------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
+
+ 8) mmc_spi.c
+ ------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
+
+ 9) mv_sdhci.c
+ -------------
+ This is a component of the SDHCI support, allowing it to run on Marvell
+ Kirkwood chip. It is probable the SDHCI support will have to be modified to
+ allow calling functions from this file based on information passed via
+ platform_data.
+
+ 10) mxcmmc.c
+ ------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
+
+ 11) mxsmmc.c
+ ------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
+
+ 12) omap_hsmmc.c
+ ----------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
+
+ 13) pxa_mmc.c
+ -------------
+ This driver uses the legacy API and is written in a severely ad-hoc manner.
+ This driver will be removed in favor of pxa_mmc_gen.c, which is proved to work
+ better and is already well tested. No conversion will be done on this driver
+ anymore.
+
+ 14) pxa_mmc_gen.c
+ -----------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
+
+ 15) s5p_mmc.c
+ -------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
+
+ 16) sdhci.c
+ -----------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple, though it'd be necessary to modify this driver
+ to also support the Kirkwood series and probably also Tegra series of CPUs.
+ See the respective parts of this section for details.
+
+ 17) sh_mmcif.c
+ --------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
+
+ 18) tegra2_mmc.c
+ ----------------
+ Follows the new API and also has a good encapsulation of the whole driver. The
+ conversion here will be simple.
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