Generalise three-wire interface to generic SPI interface.

Update rtl8139 driver to instantiate an SPI interface with a three-wire
device attached.

src/drivers/bitbash/spi_bit.c

@@ -0,0 +1,165 @@
+/*
+ * 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.
+ */
+
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+#include <errno.h>
+#include <assert.h>
+#include <timer.h>
+#include <gpxe/bitbash.h>
+#include <gpxe/spi.h>
+
+/** @file
+ *
+ * SPI bit-bashing interface
+ *
+ */
+
+/** Delay between SCLK changes and around SS changes */
+static void spi_delay ( void ) {
+	udelay ( SPI_UDELAY );
+}
+
+/**
+ * Select/deselect slave
+ *
+ * @v spi		SPI bit-bashing interface
+ * @v slave		Slave number
+ * @v state		Slave select state
+ *
+ * @c state must be set to zero to select the specified slave, or to
+ * @c SPI_MODE_SSPOL to deselect the 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->spi.mode & SPI_MODE_SSPOL );
+	DBG ( "Setting slave %d select %s\n", slave,
+	      ( state ? "high" : "low" ) );
+
+	spi_delay();
+	write_bit ( basher, SPI_BIT_SS ( slave ), state );
+	spi_delay();
+}
+
+/**
+ * Select slave
+ *
+ * @v spi		SPI interface
+ * @v slave		Slave number
+ */
+static void spi_bit_select_slave ( struct spi_interface *spi,
+				   unsigned int slave ) {
+	struct spi_bit_basher *spibit
+		= container_of ( spi, struct spi_bit_basher, spi );
+
+	spibit->slave = slave;
+	spi_bit_set_slave_select ( spibit, slave, 0 );
+}
+
+/**
+ * Deselect slave
+ *
+ * @v spi		SPI interface
+ */
+static void spi_bit_deselect_slave ( struct spi_interface *spi ) {
+	struct spi_bit_basher *spibit
+		= container_of ( spi, struct spi_bit_basher, spi );
+
+	spi_bit_set_slave_select ( spibit, spibit->slave, SPI_MODE_SSPOL );
+}
+
+/**
+ * Transfer bits over SPI bit-bashing interface
+ *
+ * @v spi		SPI interface
+ * @v data_out		TX data buffer (or NULL)
+ * @v data_in		RX data buffer (or NULL)
+ * @v len		Length of transfer (in @b bits)
+ *
+ * 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_interface *spi, const void *data_out,
+			       void *data_in, unsigned int len ) {
+	struct spi_bit_basher *spibit
+		= container_of ( spi, struct spi_bit_basher, spi );
+	struct bit_basher *basher = &spibit->basher;
+	unsigned int sclk = ( ( spi->mode & SPI_MODE_CPOL ) ? 1 : 0 );
+	unsigned int cpha = ( ( spi->mode & SPI_MODE_CPHA ) ? 1 : 0 );
+	unsigned int offset;
+	unsigned int mask;
+	unsigned int bit;
+	int step;
+
+	DBG ( "Transferring %d bits in mode %x\n", len, spi->mode );
+
+	for ( step = ( ( len * 2 ) - 1 ) ; step >= 0 ; step-- ) {
+		/* Calculate byte offset within data and bit mask */
+		offset = ( step / 16 );
+		mask = ( 1 << ( ( step % 16 ) / 2 ) );
+		
+		/* Shift data in or out */
+		if ( sclk == cpha ) {
+			const uint8_t *byte;
+
+			/* Shift data out */
+			if ( data_out ) {
+				byte = ( data_out + offset );
+				bit = ( *byte & mask );
+			} 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 ) {
+				byte = ( data_in + offset );
+				*byte &= ~mask;
+				*byte |= ( bit & mask );
+			}
+		}
+
+		/* Toggle clock line */
+		spi_delay();
+		sclk = ~sclk;
+		write_bit ( basher, SPI_BIT_SCLK, sclk );
+	}
+}
+
+/**
+ * Initialise SPI bit-bashing interface
+ *
+ * @v spibit		SPI bit-bashing interface
+ */
+void init_spi_bit_basher ( struct spi_bit_basher *spibit ) {
+	assert ( &spibit->basher.read != NULL );
+	assert ( &spibit->basher.write != NULL );
+	spibit->spi.select_slave = spi_bit_select_slave;
+	spibit->spi.deselect_slave = spi_bit_deselect_slave;
+	spibit->spi.transfer = spi_bit_transfer;
+}