src/drivers/bitbash/spi_bit.c

   1 /*
   2  * Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License as
   6  * published by the Free Software Foundation; either version 2 of the
   7  * License, or any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  17  */
  18
  19 #include <stddef.h>
  20 #include <stdint.h>
  21 #include <string.h>
  22 #include <byteswap.h>
  23 #include <errno.h>
  24 #include <assert.h>
  25 #include <timer.h>
  26 #include <gpxe/bitbash.h>
  27 #include <gpxe/spi_bit.h>
  28
  29 /** @file
  30  *
  31  * SPI bit-bashing interface
  32  *
  33  */
  34
  35 /** Delay between SCLK changes and around SS changes */
  36 static void spi_bit_delay ( void ) {
  37         udelay ( SPI_BIT_UDELAY );
  38 }
  39
  40 /** Chip select line will be asserted */
  41 #define SELECT_SLAVE 0
  42
  43 /** Chip select line will be deasserted */
  44 #define DESELECT_SLAVE SPI_MODE_SSPOL
  45
  46 /**
  47  * Select/deselect slave
  48  *
  49  * @v spibit            SPI bit-bashing interface
  50  * @v slave             Slave number
  51  * @v state             Slave select state
  52  *
  53  * @c state must be @c SELECT_SLAVE or @c DESELECT_SLAVE.
  54  */
  55 static void spi_bit_set_slave_select ( struct spi_bit_basher *spibit,
  56                                        unsigned int slave,
  57                                        unsigned int state ) {
  58         struct bit_basher *basher = &spibit->basher;
  59
  60         state ^= ( spibit->bus.mode & SPI_MODE_SSPOL );
  61         DBG ( "Setting slave %d select %s\n", slave,
  62               ( state ? "high" : "low" ) );
  63
  64         spi_bit_delay();
  65         write_bit ( basher, SPI_BIT_SS ( slave ), state );
  66         spi_bit_delay();
  67 }
  68
  69 /**
  70  * Transfer bits over SPI bit-bashing bus
  71  *
  72  * @v bus               SPI bus
  73  * @v data_out          TX data buffer (or NULL)
  74  * @v data_in           RX data buffer (or NULL)
  75  * @v len               Length of transfer (in @b bits)
  76  * @v endianness        Endianness of this data transfer
  77  *
  78  * This issues @c len clock cycles on the SPI bus, shifting out data
  79  * from the @c data_out buffer to the MOSI line and shifting in data
  80  * from the MISO line to the @c data_in buffer.  If @c data_out is
  81  * NULL, then the data sent will be all zeroes.  If @c data_in is
  82  * NULL, then the incoming data will be discarded.
  83  */
  84 static void spi_bit_transfer ( struct spi_bit_basher *spibit,
  85                                const void *data_out, void *data_in,
  86                                unsigned int len, int endianness ) {
  87         struct spi_bus *bus = &spibit->bus;
  88         struct bit_basher *basher = &spibit->basher;
  89         unsigned int sclk = ( ( bus->mode & SPI_MODE_CPOL ) ? 1 : 0 );
  90         unsigned int cpha = ( ( bus->mode & SPI_MODE_CPHA ) ? 1 : 0 );
  91         unsigned int bit_offset;
  92         unsigned int byte_offset;
  93         unsigned int byte_mask;
  94         unsigned int bit;
  95         unsigned int step;
  96
  97         DBG ( "Transferring %d bits in mode %x\n", len, bus->mode );
  98
  99         for ( step = 0 ; step < ( len * 2 ) ; step++ ) {
 100                 /* Calculate byte offset and byte mask */
 101                 bit_offset = ( ( endianness == SPI_BIT_BIG_ENDIAN ) ?
 102                                ( len - ( step / 2 ) - 1 ) : ( step / 2 ) );
 103                 byte_offset = ( bit_offset / 8 );
 104                 byte_mask = ( 1 << ( bit_offset % 8 ) );
 105
 106                 /* Shift data in or out */
 107                 if ( sclk == cpha ) {
 108                         const uint8_t *byte;
 109
 110                         /* Shift data out */
 111                         if ( data_out ) {
 112                                 byte = ( data_out + byte_offset );
 113                                 bit = ( *byte & byte_mask );
 114                         } else {
 115                                 bit = 0;
 116                         }
 117                         write_bit ( basher, SPI_BIT_MOSI, bit );
 118                 } else {
 119                         uint8_t *byte;
 120
 121                         /* Shift data in */
 122                         bit = read_bit ( basher, SPI_BIT_MISO );
 123                         if ( data_in ) {
 124                                 byte = ( data_in + byte_offset );
 125                                 *byte &= ~byte_mask;
 126                                 *byte |= ( bit & byte_mask );
 127                         }
 128                 }
 129
 130                 /* Toggle clock line */
 131                 spi_bit_delay();
 132                 sclk = ~sclk;
 133                 write_bit ( basher, SPI_BIT_SCLK, sclk );
 134         }
 135 }
 136
 137 /**
 138  * Read/write data via SPI bit-bashing bus
 139  *
 140  * @v bus               SPI bus
 141  * @v device            SPI device
 142  * @v command           Command
 143  * @v address           Address to read/write (<0 for no address)
 144  * @v data_out          TX data buffer (or NULL)
 145  * @v data_in           RX data buffer (or NULL)
 146  * @v len               Length of transfer
 147  * @ret rc              Return status code
 148  */
 149 static int spi_bit_rw ( struct spi_bus *bus, struct spi_device *device,
 150                         unsigned int command, int address,
 151                         const void *data_out, void *data_in, size_t len ) {
 152         struct spi_bit_basher *spibit
 153                 = container_of ( bus, struct spi_bit_basher, bus );
 154         uint32_t tmp;
 155
 156         /* Assert chip select on specified slave */
 157         spi_bit_set_slave_select ( spibit, device->slave, SELECT_SLAVE );
 158
 159         /* Transmit command */
 160         assert ( device->command_len <= ( 8 * sizeof ( tmp ) ) );
 161         tmp = cpu_to_le32 ( command );
 162         spi_bit_transfer ( spibit, &tmp, NULL, device->command_len,
 163                            SPI_BIT_BIG_ENDIAN );
 164
 165         /* Transmit address, if present */
 166         if ( address >= 0 ) {
 167                 assert ( device->address_len <= ( 8 * sizeof ( tmp ) ) );
 168                 tmp = cpu_to_le32 ( address );
 169                 spi_bit_transfer ( spibit, &tmp, NULL, device->address_len,
 170                                    SPI_BIT_BIG_ENDIAN );
 171         }
 172
 173         /* Transmit/receive data */
 174         spi_bit_transfer ( spibit, data_out, data_in, ( len * 8 ),
 175                            spibit->endianness );
 176
 177         /* Deassert chip select on specified slave */
 178         spi_bit_set_slave_select ( spibit, device->slave, DESELECT_SLAVE );
 179
 180         return 0;
 181 }
 182
 183 /**
 184  * Initialise SPI bit-bashing interface
 185  *
 186  * @v spibit            SPI bit-bashing interface
 187  */
 188 void init_spi_bit_basher ( struct spi_bit_basher *spibit ) {
 189         assert ( &spibit->basher.op->read != NULL );
 190         assert ( &spibit->basher.op->write != NULL );
 191         spibit->bus.rw = spi_bit_rw;
 192 }