[spi] Add address-length autodetection to the SPI bit-bashing code

Several SPI chips will respond to an SPI read command with a dummy
zero bit immediately prior to the first real data bit.  This can be
used to autodetect the address length, provided that the command
length and data length are already known, and that the MISO data line
is tied high.

Tested-by: Thomas Miletich <thomas.miletich@gmail.com>
Debugged-by: Thomas Miletich <thomas.miletich@gmail.com>

src/drivers/bitbash/spi_bit.c

 	struct bit_basher *basher = &spibit->basher;
 
 	state ^= ( spibit->bus.mode & SPI_MODE_SSPOL );
-	DBG ( "Setting slave %d select %s\n", slave,
-	      ( state ? "high" : "low" ) );
+	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 );
 	unsigned int bit;
 	unsigned int step;
 
-	DBG ( "Transferring %d bits in mode %x\n", len, bus->mode );
+	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 */
 			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;
 			}
 			/* 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 = ~sclk;
+		sclk ^= 1;
 		write_bit ( basher, SPI_BIT_SCLK, sclk );
 	}
 }
 			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;
+	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, 
 	spi_bit_set_slave_select ( spibit, device->slave, SELECT_SLAVE );
 
 	/* Transmit command */
-	assert ( device->command_len <= ( 8 * sizeof ( tmp ) ) );
-	tmp = cpu_to_le32 ( command );
-	spi_bit_transfer ( spibit, &tmp, NULL, device->command_len,
+	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 ) ) );
-		tmp = cpu_to_le32 ( address );
-		spi_bit_transfer ( spibit, &tmp, NULL, device->address_len,
-				   SPI_BIT_BIG_ENDIAN );
+		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 */

src/drivers/nvs/threewire.c

 FILE_LICENCE ( GPL2_OR_LATER );
 
 #include <stddef.h>
+#include <string.h>
 #include <assert.h>
 #include <unistd.h>
 #include <gpxe/threewire.h>
 		     void *data, size_t len ) {
 	struct spi_device *device = nvs_to_spi ( nvs );
 	struct spi_bus *bus = device->bus;
+	int rc;
 
 	assert ( bus->mode == SPI_MODE_THREEWIRE );
 
-	DBG ( "3wire %p reading %zd bytes at %04x\n", device, len, address );
+	DBGC ( device, "3wire %p reading %zd bytes at %04x\n",
+	       device, len, address );
+
+	if ( ( rc = bus->rw ( bus, device, THREEWIRE_READ, address,
+			      NULL, data, len ) ) != 0 ) {
+		DBGC ( device, "3wire %p could not read: %s\n",
+		       device, strerror ( rc ) );
+		return rc;
+	}
 
-	return bus->rw ( bus, device, THREEWIRE_READ, address,
-			 NULL, data, len );
+	return 0;
 }
 
 /**
 
 	assert ( bus->mode == SPI_MODE_THREEWIRE );
 
-	DBG ( "3wire %p writing %zd bytes at %04x\n", device, len, address );
+	DBGC ( device, "3wire %p writing %zd bytes at %04x\n",
+	       device, len, address );
 
 	/* Enable device for writing */
 	if ( ( rc = bus->rw ( bus, device, THREEWIRE_EWEN,
-			      THREEWIRE_EWEN_ADDRESS, NULL, NULL, 0 ) ) != 0 )
+			      THREEWIRE_EWEN_ADDRESS, NULL, NULL, 0 ) ) != 0 ){
+		DBGC ( device, "3wire %p could not enable writing: %s\n",
+		       device, strerror ( rc ) );
 		return rc;
+	}
 
 	/* Write data */
 	if ( ( rc = bus->rw ( bus, device, THREEWIRE_WRITE, address,
-			      data, NULL, len ) ) != 0 )
+			      data, NULL, len ) ) != 0 ) {
+		DBGC ( device, "3wire %p could not write: %s\n",
+		       device, strerror ( rc ) );
 		return rc;
+	}
 
 	/* Our model of an SPI bus doesn't provide a mechanism for
 	 * "assert CS, wait for MISO to become high, so just wait for
 
 	return 0;
 }
+
+/**
+ * Autodetect device address length
+ *
+ * @v device		SPI device
+ * @ret rc		Return status code
+ */
+int threewire_detect_address_len ( struct spi_device *device ) {
+	struct nvs_device *nvs = &device->nvs;
+	int rc;
+
+	DBGC ( device, "3wire %p autodetecting address length\n", device );
+
+	device->address_len = SPI_AUTODETECT_ADDRESS_LEN;
+	if ( ( rc = threewire_read ( nvs, 0, NULL,
+				     ( 1 << nvs->word_len_log2 ) ) ) != 0 ) {
+		DBGC ( device, "3wire %p could not autodetect address "
+		       "length: %s\n", device, strerror ( rc ) );
+		return rc;
+	}
+
+	DBGC ( device, "3wire %p autodetected address length %d\n",
+	       device, device->address_len );
+	return 0;
+}

src/include/gpxe/spi.h

 	unsigned int munge_address : 1;
 };
 
+/**
+ * SPI magic autodetection address length
+ *
+ * Set @c spi_device::address_len to @c SPI_AUTODETECT_ADDRESS_LEN if
+ * the address length should be autodetected.
+ */
+#define SPI_AUTODETECT_ADDRESS_LEN 0
+
 static inline __attribute__ (( always_inline )) struct spi_device *
 nvs_to_spi ( struct nvs_device *nvs ) {
 	return container_of ( nvs, struct spi_device, nvs );

src/include/gpxe/threewire.h

 			    void *data, size_t len );
 extern int threewire_write ( struct nvs_device *nvs, unsigned int address,
 			     const void *data, size_t len );
+extern int threewire_detect_address_len ( struct spi_device *device );
 
 /**
  * @defgroup tdevs Three-wire device types