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