spi_bit.c

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/*
 * Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

FILE_LICENCE ( GPL2_OR_LATER );

#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <byteswap.h>
#include <errno.h>
#include <assert.h>
#include <unistd.h>
#include <gpxe/bitbash.h>
#include <gpxe/spi_bit.h>

/** @file
 *
 * SPI bit-bashing interface
 *
 */

/** Delay between SCLK changes and around SS changes */
static void spi_bit_delay ( void ) {
        udelay ( SPI_BIT_UDELAY );
}

/** Chip select line will be asserted */
#define SELECT_SLAVE 0

/** Chip select line will be deasserted */
#define DESELECT_SLAVE SPI_MODE_SSPOL

/**
 * Select/deselect slave
 *
 * @v spibit            SPI bit-bashing interface
 * @v slave             Slave number
 * @v state             Slave select state
 *
 * @c state must be @c SELECT_SLAVE or @c DESELECT_SLAVE.
 */
static void spi_bit_set_slave_select ( struct spi_bit_basher *spibit,
                                       unsigned int slave,
                                       unsigned int state ) {
        struct bit_basher *basher = &spibit->basher;

        state ^= ( spibit->bus.mode & SPI_MODE_SSPOL );
        DBGC2 ( spibit, "SPIBIT %p setting slave %d select %s\n",
                spibit, slave, ( state ? "high" : "low" ) );

        spi_bit_delay();
        write_bit ( basher, SPI_BIT_SS ( slave ), state );
        spi_bit_delay();
}

/**
 * Transfer bits over SPI bit-bashing bus
 *
 * @v bus               SPI bus
 * @v data_out          TX data buffer (or NULL)
 * @v data_in           RX data buffer (or NULL)
 * @v len               Length of transfer (in @b bits)
 * @v endianness        Endianness of this data transfer
 *
 * This issues @c len clock cycles on the SPI bus, shifting out data
 * from the @c data_out buffer to the MOSI line and shifting in data
 * from the MISO line to the @c data_in buffer.  If @c data_out is
 * NULL, then the data sent will be all zeroes.  If @c data_in is
 * NULL, then the incoming data will be discarded.
 */
static void spi_bit_transfer ( struct spi_bit_basher *spibit,
                               const void *data_out, void *data_in,
                               unsigned int len, int endianness ) {
        struct spi_bus *bus = &spibit->bus;
        struct bit_basher *basher = &spibit->basher;
        unsigned int sclk = ( ( bus->mode & SPI_MODE_CPOL ) ? 1 : 0 );
        unsigned int cpha = ( ( bus->mode & SPI_MODE_CPHA ) ? 1 : 0 );
        unsigned int bit_offset;
        unsigned int byte_offset;
        unsigned int byte_mask;
        unsigned int bit;
        unsigned int step;

        DBGC2 ( spibit, "SPIBIT %p transferring %d bits in mode %#x\n",
                spibit, len, bus->mode );

        for ( step = 0 ; step < ( len * 2 ) ; step++ ) {
                /* Calculate byte offset and byte mask */
                bit_offset = ( ( endianness == SPI_BIT_BIG_ENDIAN ) ?
                               ( len - ( step / 2 ) - 1 ) : ( step / 2 ) );
                byte_offset = ( bit_offset / 8 );
                byte_mask = ( 1 << ( bit_offset % 8 ) );

                /* Shift data in or out */
                if ( sclk == cpha ) {
                        const uint8_t *byte;

                        /* Shift data out */
                        if ( data_out ) {
                                byte = ( data_out + byte_offset );
                                bit = ( *byte & byte_mask );
                                DBGCP ( spibit, "SPIBIT %p wrote bit %d\n",
                                        spibit, ( bit ? 1 : 0 ) );
                        } else {
                                bit = 0;
                        }
                        write_bit ( basher, SPI_BIT_MOSI, bit );
                } else {
                        uint8_t *byte;

                        /* Shift data in */
                        bit = read_bit ( basher, SPI_BIT_MISO );
                        if ( data_in ) {
                                DBGCP ( spibit, "SPIBIT %p read bit %d\n",
                                        spibit, ( bit ? 1 : 0 ) );
                                byte = ( data_in + byte_offset );
                                *byte &= ~byte_mask;
                                *byte |= ( bit & byte_mask );
                        }
                }

                /* Toggle clock line */
                spi_bit_delay();
                sclk ^= 1;
                write_bit ( basher, SPI_BIT_SCLK, sclk );
        }
}

/**
 * Read/write data via SPI bit-bashing bus
 *
 * @v bus               SPI bus
 * @v device            SPI device
 * @v command           Command
 * @v address           Address to read/write (<0 for no address)
 * @v data_out          TX data buffer (or NULL)
 * @v data_in           RX data buffer (or NULL)
 * @v len               Length of transfer
 * @ret rc              Return status code
 */
static int spi_bit_rw ( struct spi_bus *bus, struct spi_device *device,
                        unsigned int command, int address,
                        const void *data_out, void *data_in, size_t len ) {
        struct spi_bit_basher *spibit
                = container_of ( bus, struct spi_bit_basher, bus );
        uint32_t tmp_command;
        uint32_t tmp_address;
        uint32_t tmp_address_detect;

        /* Set clock line to idle state */
        write_bit ( &spibit->basher, SPI_BIT_SCLK, 
                    ( bus->mode & SPI_MODE_CPOL ) );

        /* Assert chip select on specified slave */
        spi_bit_set_slave_select ( spibit, device->slave, SELECT_SLAVE );

        /* Transmit command */
        assert ( device->command_len <= ( 8 * sizeof ( tmp_command ) ) );
        tmp_command = cpu_to_le32 ( command );
        spi_bit_transfer ( spibit, &tmp_command, NULL, device->command_len,
                           SPI_BIT_BIG_ENDIAN );

        /* Transmit address, if present */
        if ( address >= 0 ) {
                assert ( device->address_len <= ( 8 * sizeof ( tmp_address )));
                tmp_address = cpu_to_le32 ( address );
                if ( device->address_len == SPI_AUTODETECT_ADDRESS_LEN ) {
                        /* Autodetect address length.  This relies on
                         * the device responding with a dummy zero
                         * data bit before the first real data bit.
                         */
                        DBGC ( spibit, "SPIBIT %p autodetecting device "
                               "address length\n", spibit );
                        assert ( address == 0 );
                        device->address_len = 0;
                        do {
                                spi_bit_transfer ( spibit, &tmp_address,
                                                   &tmp_address_detect, 1,
                                                   SPI_BIT_BIG_ENDIAN );
                                device->address_len++;
                        } while ( le32_to_cpu ( tmp_address_detect ) & 1 );
                        DBGC ( spibit, "SPIBIT %p autodetected device address "
                               "length %d\n", spibit, device->address_len );
                } else {
                        spi_bit_transfer ( spibit, &tmp_address, NULL,
                                           device->address_len,
                                           SPI_BIT_BIG_ENDIAN );
                }
        }

        /* Transmit/receive data */
        spi_bit_transfer ( spibit, data_out, data_in, ( len * 8 ),
                           spibit->endianness );

        /* Deassert chip select on specified slave */
        spi_bit_set_slave_select ( spibit, device->slave, DESELECT_SLAVE );

        return 0;
}

/**
 * Initialise SPI bit-bashing interface
 *
 * @v spibit            SPI bit-bashing interface
 */
void init_spi_bit_basher ( struct spi_bit_basher *spibit ) {
        assert ( &spibit->basher.op->read != NULL );
        assert ( &spibit->basher.op->write != NULL );
        spibit->bus.rw = spi_bit_rw;
}