doc/driver-model/UDM-spi.txt

   1 The U-Boot Driver Model Project
   2 ===============================
   3 SPI analysis
   4 ============
   5 Viktor Krivak <viktor.krivak@gmail.com>
   6 2012-03-03
   7
   8 I) Overview
   9 -----------
  10
  11   1) The SPI driver
  12   -----------------
  13
  14   At this moment U-Boot provides standard API that consist of 7 functions:
  15
  16   void spi_init(void);
  17   struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs,
  18                                     unsigned int max_hz, unsigned int mode);
  19   void spi_free_slave(struct spi_slave *slave);
  20   int  spi_claim_bus(struct spi_slave *slave);
  21   void spi_release_bus(struct spi_slave *slave);
  22   int  spi_xfer(struct spi_slave *slave, unsigned int bitlen,
  23                 const void *dout, void *din, unsigned long flags);
  24   int  spi_cs_is_valid(unsigned int bus, unsigned int cs);
  25   void spi_cs_activate(struct spi_slave *slave);
  26   void spi_cs_deactivate(struct spi_slave *slave);
  27   void spi_set_speed(struct spi_slave *slave, uint hz);
  28
  29   Method spi_init() is usually empty. All necessary configuration are sets by
  30   spi_setup_slave(). But this configuration is usually stored only in memory.
  31   No real hardware sets are made. All hardware settings are provided by method
  32   spi_claim_bus(). This method claims the bus and it can't be claimed again
  33   until it's release. That's mean all calls of method spi_claim_bus() will
  34   fail. But lots of cpu implementation don't meet this behaviour.
  35   Method spi_release_bus() does exact opposite. It release bus directly by
  36   some hardware sets. spi_free_slave() only free memory allocated by
  37   spi_setup_slave(). Method spi_xfer() do actually read and write operation
  38   throw specified bus and cs. Other methods are self explanatory.
  39
  40   2) Current limitations
  41   ----------------------
  42
  43   Theoretically at this moment api allows use more then one bus per device at
  44   the time. But in real this can be achieved only when all buses have their
  45   own base addresses in memory.
  46
  47
  48 II) Approach
  49 ------------
  50
  51   1) Claiming bus
  52   ---------------
  53
  54   The current api cannot be used because struct spi_slave have to be in
  55   private data. In that case user are prohibited to use different bus on one
  56   device at same time. But when base memory address for bus are different.
  57   It's possible make more instance of this driver. Otherwise it can't can be
  58   done because of hardware limitation.
  59
  60   2) API change
  61   -------------
  62
  63   Method spi_init() is moved to probe. Methods spi_setup_slave() and
  64   spi_claim_bus() are joined to one method. This method checks if desired bus
  65   exists and is available then configure necessary hardware and claims bus.
  66   Method spi_release_bus() and spi_free_slave() are also joined to meet this
  67   new approach. Other function remain same. Only struct spi_slave was change
  68   to instance.
  69
  70   struct ops {
  71     int  (*spi_request_bus)(struct instance *i, unsigned int bus,
  72                             unsigned int cs, unsigned int max_hz,
  73                             unsigned int mode);
  74     void (*spi_release_bus)(struct instance *i);
  75     int  (*spi_xfer) (struct instance *i, unsigned int bitlen,
  76                       const void *dout, void *din, unsigned long flags);
  77     int  (*spi_cs_is_valid)(struct instance *i, unsigned int bus,
  78                             unsigned int cs);
  79     void (*spi_cs_activate)(struct instance *i);
  80     void (*spi_cs_deactivate)(struct instance *i);
  81     void (*spi_set_speed)(struct instance *i, uint hz);
  82   }
  83
  84   3) Legacy API
  85   -------------
  86
  87   To easy conversion of the whole driver. Original and new api can exist next
  88   to each other. New API is designed to be only a wrapper that extracts
  89   necessary information from private_data and use old api. When driver can
  90   use more than one bus at the time. New API require multiple instance. One
  91   for each bus. In this case spi_slave have to be copied in each instance.
  92
  93   4) Conversion TIME-LINE
  94   -----------------------
  95
  96   To prevent build corruption api conversion have to be processed in several
  97   independent steps. In first step all old API methods are renamed. After that
  98   new API and core function are implemented. Next step is conversion of all
  99   board init methods to set platform data. After all these steps it is possible
 100   to start conversion of all remaining calls. This procedure guarantees that
 101   build procedure and binaries are never broken.
 102
 103 III) Analysis of in-tree drivers
 104 --------------------------------
 105
 106   altera_spi.c
 107   ------------
 108   All methods have designated structure. Simple conversion possible.
 109
 110   andes_spi.c
 111   -----------
 112   All methods have designated structure. Simple conversion possible.
 113
 114   andes_spi.h
 115   -----------
 116   Support file for andes_spi.c. No conversion is needed.
 117
 118   armada100_spi.c
 119   ---------------
 120   All methods have designated structure. Simple conversion possible.
 121
 122   atmel_dataflash_spi.c
 123   ---------------------
 124   Wrong placement. Will be moved to another location.
 125
 126   atmel_spi.c
 127   -----------
 128   Supports more than one bus. Need some minor change.
 129
 130   atmel_spi.h
 131   -----------
 132   Support file for andes_spi.c. No conversion is needed.
 133
 134   bfin_spi.c
 135   ----------
 136   Supports more than one bus. Need some minor change.
 137
 138   cf_spi.c
 139   --------
 140   Cooperate with some cpu specific methods from other files. Hard conversion.
 141
 142   davinci_spi.c
 143   -------------
 144   All methods have designated structure. Simple conversion possible.
 145
 146   davinci_spi.h
 147   -------------
 148   Support file for davinci_spi.h. No conversion is needed.
 149
 150   fsl_espi.c
 151   ----------
 152   All methods have designated structure. Simple conversion possible.
 153
 154   kirkwood_spi.c
 155   --------------
 156   All methods have designated structure. Simple conversion possible.
 157
 158   mpc8xxx_spi.c
 159   -------------
 160   All methods have designated structure. Simple conversion possible.
 161
 162   mpc52xx_spi.c
 163   -------------
 164   All methods have designated structure. Simple conversion possible.
 165
 166   mxc_spi.c
 167   ---------
 168   All methods have designated structure. Simple conversion possible.
 169
 170   mxs_spi.c
 171   ---------
 172   All methods have designated structure. Simple conversion possible.
 173
 174   oc_tiny_spi.c
 175   -------------
 176   Supports more than one bus. Need some minor change.
 177
 178   omap3_spi.c
 179   -----------
 180   Supports more than one bus. Need some minor change.
 181
 182   omap3_spi.h
 183   -----------
 184   Support file for omap3_spi.c. No conversion is needed.
 185
 186   sh_spi.c
 187   --------
 188   All methods have designated structure. Simple conversion possible.
 189
 190   sh_spi.h
 191   --------
 192   Support file for sh_spi.h. No conversion is needed.
 193
 194   soft_spi.c
 195   ----------
 196   Use many board specific method linked from other files. Need careful debugging.
 197
 198   tegra2_spi.c
 199   ------------
 200   Some hardware specific problem when releasing bus.