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| -rw-r--r-- | doc/driver-model/UDM-block.txt | 279 |
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diff --git a/doc/driver-model/UDM-block.txt b/doc/driver-model/UDM-block.txt new file mode 100644 index 0000000..5d5c776 --- /dev/null +++ b/doc/driver-model/UDM-block.txt @@ -0,0 +1,279 @@ +The U-Boot Driver Model Project +=============================== +Block device subsystem analysis +=============================== + +Pavel Herrmann <morpheus.ibis@gmail.com> +2012-03-08 + +I) Overview +----------- + + U-Boot currently implements several distinct APIs for block devices - some + drivers use the SATA API, some drivers use the IDE API, sym53c8xx and + AHCI use the SCSI API, mg_disk has a separate API, and systemace also has a + separate API. There are also MMC and USB APIs used outside of drivers/block, + those will be detailed in their specific documents. + + Block devices are described by block_dev_desc structure, that holds, among + other things, the read/write/erase callbacks. Block device structures are + stored in any way depending on the API, but can be accessed by + + block_dev_desc_t * $api_get_dev(int dev) + + function, as seen in disk/part.c. + + 1) SATA interface + ----------------- + + The SATA interface drivers implement the following functions: + + int init_sata(int dev) + int scan_sata(int dev) + ulong sata_read(int dev, ulong blknr, ulong blkcnt, void *buffer) + ulong sata_write(int dev, ulong blknr, ulong blkcnt, const void *buffer) + + Block devices are kept in sata_dev_desc[], which is prefilled with values + common to all SATA devices in cmd_sata.c, and then modified in init_sata + function in the drivers. Callbacks of the block device use SATA API + directly. The sata_get_dev function is defined in cmd_sata.c. + + 2) SCSI interface + ----------------- + + The SCSI interface drivers implement the following functions: + + void scsi_print_error(ccb *pccb) + int scsi_exec(ccb *pccb) + void scsi_bus_reset(void) + void scsi_low_level_init(int busdevfunc) + + The SCSI API works through the scsi_exec function, the actual operation + requested is found in the ccb structure. + + Block devices are kept in scsi_dev_desc[], which lives only in cmd_scsi.c. + Callbacks of the block device use functions from cmd_scsi.c, which in turn + call scsi_exec of the controller. The scsi_get_dev function is also defined + in cmd_scsi.c. + + 3) mg_disk interface + -------------------- + + The mg_disk interface drivers implement the following functions: + + struct mg_drv_data* mg_get_drv_data (void) + uint mg_disk_init (void) + uint mg_disk_read (u32 addr, u8 *buff, u32 len) + uint mg_disk_write(u32 addr, u8 *buff, u32 len) + uint mg_disk_write_sects(void *buff, u32 sect_num, u32 sect_cnt) + uint mg_disk_read_sects(void *buff, u32 sect_num, u32 sect_cnt) + + The mg_get_drv_data function is to be overridden per-board, but there are no + board in-tree that do this. + + Only one driver for this API exists, and it only supports one block device. + Callbacks for this device are implemented in mg_disk.c and call the mg_disk + API. The mg_disk_get_dev function is defined in mg_disk.c and ignores the + device number, always returning the same device. + + 4) systemace interface + ---------------------- + + The systemace interface does not define any driver API, and has no command + itself. The single defined function is systemace_get_devs() from + systemace.c, which returns a single static structure for the only supported + block device. Callbacks for this device are also implemented in systemace.c. + + 5) IDE interface + ---------------- + + The IDE interface drivers implement the following functions, but only if + CONFIG_IDE_AHB is set: + + uchar ide_read_register(int dev, unsigned int port); + void ide_write_register(int dev, unsigned int port, unsigned char val); + void ide_read_data(int dev, ulong *sect_buf, int words); + void ide_write_data(int dev, ulong *sect_buf, int words); + + The first two functions are called from ide_inb()/ide_outb(), and will + default to direct memory access if CONFIG_IDE_AHB is not set, or + ide_inb()/ide_outb() functions will get overridden by the board altogether. + + The second two functions are called from input_data()/output_data() + functions, and also default to direct memory access, but cannot be + overridden by the board. + + One function shared by IDE drivers (but not defined in ide.h) is + int ide_preinit(void) + This function gets called from ide_init in cmd_ide.c if CONFIG_IDE_PREINIT + is defined, and will do the driver-specific initialization of the device. + + Block devices are kept in ide_dev_desc[], which is filled in cmd_ide.c. + Callbacks of the block device are defined in cmd_ide.c, and use the + ide_inb()/ide_outb()/input_data()/output_data() functions mentioned above. + The ide_get_dev function is defined in cmd_ide.c. + +II) Approach +------------ + + A new block controller core and an associated API will be created to mimic the + current SATA API, its drivers will have the following ops: + + struct block_ctrl_ops { + int scan(instance *i); + int reset(instance *i, int port); + lbaint_t read(instance *i, int port, lbaint_t start, lbatin_t length, + void *buffer); + lbaint_t write(instance *i, int port, lbaint_t start, lbatin_t length, + void*buffer); + } + + The current sata_init() function will be changed into the driver probe() + function. The read() and write() functions should never be called directly, + instead they should be called by block device driver for disks. + + Other block APIs would either be transformed into this API, or be kept as + legacy for old drivers, or be dropped altogether. + + Legacy driver APIs will each have its own driver core that will contain the + shared logic, which is currently located mostly in cmd_* files. Callbacks for + block device drivers will then probably be implemented as a part of the core + logic, and will use the driver ops (which will copy current state of + respective APIs) to do the work. + + All drivers will be cleaned up, most ifdefs should be converted into + platform_data, to enable support for multiple devices with different settings. + + A new block device core will also be created, and will keep track of all + block devices on all interfaces. + + Current block_dev_desc structure will be changed to fit the driver model, all + identification and configuration will be placed in private data, and + a single accessor and modifier will be defined, to accommodate the need for + different sets of options for different interfaces, while keeping the + structure small. The new block device drivers will have the following ops + structure (lbaint_t is either 32bit or 64bit unsigned, depending on + CONFIG_LBA48): + + struct blockdev_ops { + lbaint_t (*block_read)(struct instance *i, lbaint_t start, lbaint_t blkcnt, + void *buffer); + lbaint_t (*block_write)(struct instance *i, lbaint_t start, lbaint_t blkcnt, + void *buffer); + lbaint_t (*block_erase)(struct instance *i, lbaint_t start, lbaint_t blkcnt + ); + int (*get_option)(struct instance *i, enum blockdev_option_code op, + struct option *res); + int (*set_option)(struct instance *i, enum blockdev_option_code op, + struct option *val); + } + + struct option { + uint32_t flags + union data { + uint64_t data_u; + char* data_s; + void* data_p; + } + } + + enum blockdev_option_code { + BLKD_OPT_IFTYPE=0, + BLKD_OPT_TYPE, + BLKD_OPT_BLOCKSIZE, + BLKD_OPT_BLOCKCOUNT, + BLKD_OPT_REMOVABLE, + BLKD_OPT_LBA48, + BLKD_OPT_VENDOR, + BLKD_OPT_PRODICT, + BLKD_OPT_REVISION, + BLKD_OPT_SCSILUN, + BLKD_OPT_SCSITARGET, + BLKD_OPT_OFFSET + } + + Flags in option above will contain the type of returned data (which should be + checked against what is expected, even though the option requested should + specify it), and a flag to indicate whether the returned pointer needs to be + free()'d. + + The block device core will contain the logic now located in disk/part.c and + related files, and will be used to forward requests to block devices. The API + for the block device core will copy the ops of a block device (with a string + identifier instead of instance pointer). This means that partitions will also + be handled by the block device core, and exported as block devices, making + them transparent to the rest of the code. + + Sadly, this will change how file systems can access the devices, and thus will + affect a lot of places. However, these changes should be localized and easy to + implement. + + AHCI driver will be rewritten to fit the new unified block controller API, + making SCSI API easy to merge with sym53c8xx, or remove it once the device + driver has died. + + Optionally, IDE core may be changed into one driver with unified block + controller API, as most of it is already in one place and device drivers are + just sets of hooks. Additionally, mg_disk driver is unused and may be removed + in near future. + + + +III) Analysis of in-tree drivers +-------------------------------- + + 1) ahci.c + --------- + SCSI API, will be rewritten for a different API. + + 2) ata_piix.c + ------------- + SATA API, easy to port. + + 3) fsl_sata.c + ------------- + SATA API, few CONFIG macros, easy to port. + + 4) ftide020.c + ------------- + IDE API, defines CONFIG_IDE_AHB and ide_preinit hook functions. + + 5) mg_disk.c + ------------ + Single driver with mg_disk API, not much to change, easy to port. + + 6) mvsata_ide.c + --------------- + IDE API, only defines ide_preinit hook function. + + 7) mxc_ata.c + ------------ + IDE API, only defines ide_preinit hook function. + + 8) pata_bfin.c + -------------- + SATA API, easy to port. + + 9) sata_dwc.c + ------------- + SATA API, easy to port. + + 10) sata_sil3114.c + ------------------ + SATA API, easy to port. + + 11) sata_sil.c + -------------- + SATA API, easy to port. + + 12) sil680.c + ------------ + IDE API, only defines ide_preinit hook function. + + 13) sym53c8xx.c + --------------- + SCSI API, may be merged with code from cmd_scsi. + + 14) systemace.c + --------------- + Single driver with systemace API, not much to change, easy to port. |