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