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Diffstat (limited to 'doc/driver-model/UDM-spi.txt')
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diff --git a/doc/driver-model/UDM-spi.txt b/doc/driver-model/UDM-spi.txt new file mode 100644 index 0000000..7442a32 --- /dev/null +++ b/doc/driver-model/UDM-spi.txt @@ -0,0 +1,200 @@ +The U-Boot Driver Model Project +=============================== +SPI analysis +============ +Viktor Krivak <viktor.krivak@gmail.com> +2012-03-03 + +I) Overview +----------- + + 1) The SPI driver + ----------------- + + At this moment U-Boot provides standard API that consist of 7 functions: + + void spi_init(void); + struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs, + unsigned int max_hz, unsigned int mode); + void spi_free_slave(struct spi_slave *slave); + int spi_claim_bus(struct spi_slave *slave); + void spi_release_bus(struct spi_slave *slave); + int spi_xfer(struct spi_slave *slave, unsigned int bitlen, + const void *dout, void *din, unsigned long flags); + int spi_cs_is_valid(unsigned int bus, unsigned int cs); + void spi_cs_activate(struct spi_slave *slave); + void spi_cs_deactivate(struct spi_slave *slave); + void spi_set_speed(struct spi_slave *slave, uint hz); + + Method spi_init() is usually empty. All necessary configuration are sets by + spi_setup_slave(). But this configuration is usually stored only in memory. + No real hardware sets are made. All hardware settings are provided by method + spi_claim_bus(). This method claims the bus and it can't be claimed again + until it's release. That's mean all calls of method spi_claim_bus() will + fail. But lots of cpu implementation don't meet this behaviour. + Method spi_release_bus() does exact opposite. It release bus directly by + some hardware sets. spi_free_slave() only free memory allocated by + spi_setup_slave(). Method spi_xfer() do actually read and write operation + throw specified bus and cs. Other methods are self explanatory. + + 2) Current limitations + ---------------------- + + Theoretically at this moment api allows use more then one bus per device at + the time. But in real this can be achieved only when all buses have their + own base addresses in memory. + + +II) Approach +------------ + + 1) Claiming bus + --------------- + + The current api cannot be used because struct spi_slave have to be in + private data. In that case user are prohibited to use different bus on one + device at same time. But when base memory address for bus are different. + It's possible make more instance of this driver. Otherwise it can't can be + done because of hardware limitation. + + 2) API change + ------------- + + Method spi_init() is moved to probe. Methods spi_setup_slave() and + spi_claim_bus() are joined to one method. This method checks if desired bus + exists and is available then configure necessary hardware and claims bus. + Method spi_release_bus() and spi_free_slave() are also joined to meet this + new approach. Other function remain same. Only struct spi_slave was change + to instance. + + struct ops { + int (*spi_request_bus)(struct instance *i, unsigned int bus, + unsigned int cs, unsigned int max_hz, + unsigned int mode); + void (*spi_release_bus)(struct instance *i); + int (*spi_xfer) (struct instance *i, unsigned int bitlen, + const void *dout, void *din, unsigned long flags); + int (*spi_cs_is_valid)(struct instance *i, unsigned int bus, + unsigned int cs); + void (*spi_cs_activate)(struct instance *i); + void (*spi_cs_deactivate)(struct instance *i); + void (*spi_set_speed)(struct instance *i, uint hz); + } + + 3) Legacy API + ------------- + + To easy conversion of the whole driver. Original and new api can exist next + to each other. New API is designed to be only a wrapper that extracts + necessary information from private_data and use old api. When driver can + use more than one bus at the time. New API require multiple instance. One + for each bus. In this case spi_slave have to be copied in each instance. + + 4) Conversion TIME-LINE + ----------------------- + + To prevent build corruption api conversion have to be processed in several + independent steps. In first step all old API methods are renamed. After that + new API and core function are implemented. Next step is conversion of all + board init methods to set platform data. After all these steps it is possible + to start conversion of all remaining calls. This procedure guarantees that + build procedure and binaries are never broken. + +III) Analysis of in-tree drivers +-------------------------------- + + 1) altera_spi.c + --------------- + All methods have designated structure. Simple conversion possible. + + 2) andes_spi.c + -------------- + All methods have designated structure. Simple conversion possible. + + 3) andes_spi.h + -------------- + Support file for andes_spi.c. No conversion is needed. + + 4) armada100_spi.c + ------------------ + All methods have designated structure. Simple conversion possible. + + 5) atmel_dataflash_spi.c + ------------------------ + Wrong placement. Will be moved to another location. + + 6) atmel_spi.c + -------------- + Supports more than one bus. Need some minor change. + + 7) atmel_spi.h + -------------- + Support file for andes_spi.c. No conversion is needed. + + 8) bfin_spi.c + ------------- + Supports more than one bus. Need some minor change. + + 9) cf_spi.c + ----------- + Cooperate with some cpu specific methods from other files. Hard conversion. + + 10) davinci_spi.c + ----------------- + All methods have designated structure. Simple conversion possible. + + 11) davinci_spi.h + ----------------- + Support file for davinci_spi.h. No conversion is needed. + + 12) fsl_espi.c + -------------- + All methods have designated structure. Simple conversion possible. + + 13) kirkwood_spi.c + ------------------ + All methods have designated structure. Simple conversion possible. + + 14) mpc8xxx_spi.c + ----------------- + All methods have designated structure. Simple conversion possible. + + 15) mpc52xx_spi.c + ----------------- + All methods have designated structure. Simple conversion possible. + + 16) mxc_spi.c + ------------- + All methods have designated structure. Simple conversion possible. + + 17) mxs_spi.c + ------------- + All methods have designated structure. Simple conversion possible. + + 18) oc_tiny_spi.c + ----------------- + Supports more than one bus. Need some minor change. + + 19) omap3_spi.c + --------------- + Supports more than one bus. Need some minor change. + + 20) omap3_spi.h + --------------- + Support file for omap3_spi.c. No conversion is needed. + + 21) sh_spi.c + ------------ + All methods have designated structure. Simple conversion possible. + + 22) sh_spi.h + ------------ + Support file for sh_spi.h. No conversion is needed. + + 23) soft_spi.c + -------------- + Use many board specific method linked from other files. Need careful debugging. + + 24) tegra2_spi.c + ---------------- + Some hardware specific problem when releasing bus. |