[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

@@ -60,8 +60,8 @@ static void spi_bit_set_slave_select ( struct spi_bit_basher *spibit,
 	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 );
@@ -96,7 +96,8 @@ static void spi_bit_transfer ( struct spi_bit_basher *spibit,
 	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 */
@@ -113,6 +114,8 @@ static void spi_bit_transfer ( struct spi_bit_basher *spibit,
 			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;
 			}
@@ -123,6 +126,8 @@ static void spi_bit_transfer ( struct spi_bit_basher *spibit,
 			/* 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 );
@@ -131,7 +136,7 @@ static void spi_bit_transfer ( struct spi_bit_basher *spibit,
 
 		/* Toggle clock line */
 		spi_bit_delay();
-		sclk = ~sclk;
+		sclk ^= 1;
 		write_bit ( basher, SPI_BIT_SCLK, sclk );
 	}
 }
@@ -153,7 +158,9 @@ static int spi_bit_rw ( struct spi_bus *bus, struct spi_device *device,
 			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, 
@@ -163,17 +170,37 @@ static int spi_bit_rw ( struct spi_bus *bus, struct spi_device *device,
 	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

@@ -19,6 +19,7 @@
 FILE_LICENCE ( GPL2_OR_LATER );
 
 #include <stddef.h>
+#include <string.h>
 #include <assert.h>
 #include <unistd.h>
 #include <gpxe/threewire.h>
@@ -42,13 +43,21 @@ int threewire_read ( struct nvs_device *nvs, unsigned int address,
 		     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;
 }
 
 /**
@@ -68,17 +77,24 @@ int threewire_write ( struct nvs_device *nvs, unsigned int address,
 
 	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
@@ -88,3 +104,28 @@ int threewire_write ( struct nvs_device *nvs, unsigned int address,
 
 	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

@@ -104,6 +104,14 @@ struct spi_device {
 	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

@@ -45,6 +45,7 @@ extern int threewire_read ( struct nvs_device *nvs, unsigned int address,
 			    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