libpayload/ahci: Fix a warning by decompartmentalise the AHCI driver.

Decompartmentalise AHCI driver into two parts, ATA and ATAPI. Add a few
superficial comments while here. This also fixes a compiler warning.

Change-Id: Ia1fd545b39868a81cbc311f6ffc786f9f1f61415
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/4783
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

5 files changed, 452 insertions, 273 deletions

diff --git a/payloads/libpayload/drivers/storage/ahci.c b/payloads/libpayload/drivers/storage/ahci.c
index ec4db4ca7a..5711fa263d 100644
--- a/payloads/libpayload/drivers/storage/ahci.c
+++ b/payloads/libpayload/drivers/storage/ahci.c
@@ -71,54 +71,8 @@ static inline int ahci_port_is_active(const hba_port_t *const port)
 		== (HBA_PxSSTS_IPM_ACTIVE | HBA_PxSSTS_DET_ESTABLISHED);
 }
 
-static int ahci_cmdengine_start(hba_port_t *const port)
-{
-	/* CR has to be clear before starting the command engine.
-	   This shouldn't take too long, but we should time out nevertheless. */
-	int timeout = 1000; /* Time out after 1000 * 1us == 1ms. */
-	while ((port->cmd_stat & HBA_PxCMD_CR) && timeout--)
-		udelay(1);
-	if (timeout < 0) {
-		printf("ahci: Timeout during start of command engine.\n");
-		return 1;
-	}
-
-	port->cmd_stat |= HBA_PxCMD_FRE;
-	port->cmd_stat |= HBA_PxCMD_ST;
-	return 0;
-}
-
-static int ahci_cmdengine_stop(hba_port_t *const port)
-{
-	port->cmd_stat &= ~HBA_PxCMD_ST;
-
-	/* Wait for the controller to clear CR.
-	   This shouldn't take too long, but we should time out nevertheless. */
-	int timeout = 1000; /* Time out after 1000 * 1us == 1ms. */
-	while ((port->cmd_stat & HBA_PxCMD_CR) && timeout--)
-		udelay(1);
-	if (timeout < 0) {
-		printf("ahci: Timeout during stopping of command engine.\n");
-		return 1;
-	}
-
-	port->cmd_stat &= ~HBA_PxCMD_FRE;
-
-	/* Wait for the controller to clear FR.
-	   This shouldn't take too long, but we should time out nevertheless. */
-	timeout = 1000; /* Time out after 1000 * 1us == 1ms. */
-	while ((port->cmd_stat & HBA_PxCMD_FR) && timeout--)
-		udelay(1);
-	if (timeout < 0) {
-		printf("ahci: Timeout during stopping of command engine.\n");
-		return 1;
-	}
-
-	return 0;
-}
-
 /** Do minimal error recovery. */
-static int ahci_error_recovery(ahci_dev_t *const dev, const u32 intr_status)
+int ahci_error_recovery(ahci_dev_t *const dev, const u32 intr_status)
 {
 	/* Command engine has to be restarted.
 	   We don't call ahci_cmdengine_stop() here as it also checks
@@ -145,231 +99,6 @@ static int ahci_error_recovery(ahci_dev_t *const dev, const u32 intr_status)
 		return -1;
 }
 
-/** Give a buffer with even address. */
-static u8 *ahci_prdbuf_init(ahci_dev_t *const dev,
-			    u8 *const user_buf, const size_t len,
-			    const int out)
-{
-	if ((u32)user_buf & 1) {
-		printf("ahci: Odd buffer pointer (%p).\n", user_buf);
-		if (dev->buf) /* orphaned buffer */
-			free((void *)dev->buf - *(dev->buf - 1));
-		dev->buf = malloc(len + 2);
-		if (!dev->buf)
-			return NULL;
-		dev->user_buf = user_buf;
-		dev->write_back = !out;
-		dev->buflen = len;
-		if ((u32)dev->buf & 1) {
-			dev->buf[0] = 1;
-			dev->buf += 1;
-		} else {
-			dev->buf[0] = 1;
-			dev->buf[1] = 2;
-			dev->buf += 2;
-		}
-		if (out)
-			memcpy(dev->buf, user_buf, len);
-		return dev->buf;
-	} else {
-		return user_buf;
-	}
-}
-
-static void ahci_prdbuf_finalize(ahci_dev_t *const dev)
-{
-	if (dev->buf) {
-		if (dev->write_back)
-			memcpy(dev->user_buf, dev->buf, dev->buflen);
-		free((void *)dev->buf - *(dev->buf - 1));
-	}
-	dev->buf = NULL;
-	dev->user_buf = NULL;
-	dev->write_back = 0;
-	dev->buflen = 0;
-}
-
-static ssize_t ahci_cmdslot_exec(ahci_dev_t *const dev)
-{
-	const int slotnum = 0; /* We always use the first slot. */
-
-	if (!(dev->port->cmd_stat & HBA_PxCMD_CR))
-		return -1;
-
-	/* Trigger command execution. */
-	dev->port->cmd_issue |= (1 << slotnum);
-
-	/* Wait for the controller to finish command execution. */
-	int timeout = 50000; /* Time out after 50000 * 100us == 5s. */
-	while ((dev->port->cmd_issue & (1 << slotnum)) &&
-			!(dev->port->intr_status & HBA_PxIS_TFES) &&
-			timeout--)
-		udelay(100);
-	if (timeout < 0) {
-		printf("ahci: Timeout during command execution.\n");
-		return -1;
-	}
-
-	ahci_prdbuf_finalize(dev);
-
-	const u32 intr_status = ahci_clear_status(dev->port, intr_status);
-	if (intr_status & (HBA_PxIS_FATAL | HBA_PxIS_PCS)) {
-		ahci_error_recovery(dev, intr_status);
-		return -1;
-	} else {
-		return dev->cmdlist[slotnum].prd_bytes;
-	}
-}
-
-static size_t ahci_cmdslot_prepare(ahci_dev_t *const dev,
-				   u8 *const user_buf, size_t buf_len,
-				   const int out)
-{
-	const int slotnum = 0; /* We always use the first slot. */
-
-	size_t read_count = 0;
-
-	memset((void *)&dev->cmdlist[slotnum],
-			'\0', sizeof(dev->cmdlist[slotnum]));
-	memset((void *)dev->cmdtable,
-			'\0', sizeof(*dev->cmdtable));
-	dev->cmdlist[slotnum].cmd = CMD_CFL(FIS_H2D_FIS_LEN);
-	dev->cmdlist[slotnum].cmdtable_base = virt_to_phys(dev->cmdtable);
-
-	if (buf_len > 0) {
-		size_t prdt_len;
-		u8 *buf;
-		int i;
-
-		prdt_len = ((buf_len - 1) >> BYTES_PER_PRD_SHIFT) + 1;
-		const size_t max_prdt_len = ARRAY_SIZE(dev->cmdtable->prdt);
-		if (prdt_len > max_prdt_len) {
-			prdt_len = max_prdt_len;
-			buf_len = prdt_len << BYTES_PER_PRD_SHIFT;
-		}
-
-		dev->cmdlist[slotnum].prdt_length = prdt_len;
-		read_count = buf_len;
-
-		buf = ahci_prdbuf_init(dev, user_buf, buf_len, out);
-		if (!buf)
-			return 0;
-		for (i = 0; i < prdt_len; ++i) {
-			const size_t bytes =
-				(buf_len < BYTES_PER_PRD)
-				? buf_len : BYTES_PER_PRD;
-			dev->cmdtable->prdt[i].data_base = virt_to_phys(buf);
-			dev->cmdtable->prdt[i].flags = PRD_TABLE_BYTES(bytes);
-			buf_len -= bytes;
-			buf += bytes;
-		}
-	}
-
-	return read_count;
-}
-
-static ssize_t ahci_ata_read_sectors(ata_dev_t *const ata_dev,
-				     const lba_t start, size_t count,
-				     u8 *const buf)
-{
-	ahci_dev_t *const dev = (ahci_dev_t *)ata_dev;
-
-	if (count == 0)
-		return 0;
-
-	if (ata_dev->read_cmd == ATA_READ_DMA) {
-		if (start >= (1 << 28)) {
-		       printf("ahci: Sector is not 28-bit addressable.\n");
-		       return -1;
-		} else if (count > 256) {
-		       printf("ahci: Sector count too high (max. 256).\n");
-		       count = 256;
-		}
-#ifdef CONFIG_STORAGE_64BIT_LBA
-	} else if (ata_dev->read_cmd == ATA_READ_DMA_EXT) {
-		if (start >= (1ULL << 48)) {
-			printf("ahci: Sector is not 48-bit addressable.\n");
-			return -1;
-		} else if (count > (64 * 1024)) {
-		       printf("ahci: Sector count too high (max. 65536).\n");
-		       count = 64 * 1024;
-		}
-#endif
-	} else {
-		printf("ahci: Unsupported ATA read command (0x%x).\n",
-			ata_dev->read_cmd);
-		return -1;
-	}
-
-	const size_t bytes = count << ata_dev->sector_size_shift;
-	const size_t bytes_feasible = ahci_cmdslot_prepare(dev, buf, bytes, 0);
-	const size_t sectors = bytes_feasible >> ata_dev->sector_size_shift;
-
-	dev->cmdtable->fis[ 0] = FIS_HOST_TO_DEVICE;
-	dev->cmdtable->fis[ 1] = FIS_H2D_CMD;
-	dev->cmdtable->fis[ 2] = ata_dev->read_cmd;
-	dev->cmdtable->fis[ 4] = (start >>  0) & 0xff;
-	dev->cmdtable->fis[ 5] = (start >>  8) & 0xff;
-	dev->cmdtable->fis[ 6] = (start >> 16) & 0xff;
-	dev->cmdtable->fis[ 7] = FIS_H2D_DEV_LBA;
-	dev->cmdtable->fis[ 8] = (start >> 24) & 0xff;
-#ifdef CONFIG_STORAGE_64BIT_LBA
-	if (ata_dev->read_cmd == ATA_READ_DMA_EXT) {
-		dev->cmdtable->fis[ 9] = (start >> 32) & 0xff;
-		dev->cmdtable->fis[10] = (start >> 40) & 0xff;
-	}
-#endif
-	dev->cmdtable->fis[12] = (sectors >>  0) & 0xff;
-	dev->cmdtable->fis[13] = (sectors >>  8) & 0xff;
-
-	if (ahci_cmdslot_exec(dev) < 0)
-		return -1;
-	else
-		return dev->cmdlist->prd_bytes >> ata_dev->sector_size_shift;
-}
-
-static ssize_t ahci_packet_read_cmd(atapi_dev_t *const _dev,
-				    const u8 *const cmd, const size_t cmdlen,
-				    u8 *const buf, const size_t buflen)
-{
-	ahci_dev_t *const dev = (ahci_dev_t *)_dev;
-
-	if ((cmdlen != 12) && (cmdlen != 16)) {
-		printf("ahci: Only 12- and 16-byte packet commands allowed.\n");
-		return -1;
-	}
-
-	const size_t len = ahci_cmdslot_prepare(dev, buf, buflen, 0);
-	u16 byte_limit = MIN(len, 63 * 1024); /* like Linux */
-	if (byte_limit & 1) ++byte_limit; /* even limit */
-
-	dev->cmdlist[0].cmd |= CMD_ATAPI;
-	dev->cmdtable->fis[0] = FIS_HOST_TO_DEVICE;
-	dev->cmdtable->fis[1] = FIS_H2D_CMD;
-	dev->cmdtable->fis[2] = ATA_PACKET;
-	dev->cmdtable->fis[5] = byte_limit & 0xff;
-	dev->cmdtable->fis[6] = byte_limit >> 8;
-	memcpy((void *)dev->cmdtable->atapi_cmd, cmd, cmdlen);
-
-	return ahci_cmdslot_exec(dev);
-}
-
-static int ahci_identify_device(ata_dev_t *const ata_dev, u8 *const buf)
-{
-	ahci_dev_t *const dev = (ahci_dev_t *)ata_dev;
-
-	ahci_cmdslot_prepare(dev, buf, 512, 0);
-
-	dev->cmdtable->fis[0] = FIS_HOST_TO_DEVICE;
-	dev->cmdtable->fis[1] = FIS_H2D_CMD;
-	dev->cmdtable->fis[2] = ata_dev->identify_cmd;
-
-	if ((ahci_cmdslot_exec(dev) < 0) || (dev->cmdlist->prd_bytes != 512))
-		return -1;
-	else
-		return 0;
-}
-
 static int ahci_dev_init(hba_ctrl_t *const ctrl,
 			 hba_port_t *const port,
 			 const int portnum)
diff --git a/payloads/libpayload/drivers/storage/ahci_ata.c b/payloads/libpayload/drivers/storage/ahci_ata.c
new file mode 100644
index 0000000000..1efec23ec4
--- /dev/null
+++ b/payloads/libpayload/drivers/storage/ahci_ata.c
@@ -0,0 +1,100 @@
+/*
+ * This file is part of the libpayload project.
+ *
+ * Copyright (C) 2012 secunet Security Networks AG
+ * Copyright (C) 2013 Edward O'Callaghan <eocallaghan@alterapraxis.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <libpayload.h>
+#include <pci.h>
+#include <storage/ata.h>
+#include <storage/ahci.h>
+
+#include "ahci_private.h"
+
+
+ssize_t ahci_ata_read_sectors(ata_dev_t *const ata_dev,
+				     const lba_t start, size_t count,
+				     u8 *const buf)
+{
+	ahci_dev_t *const dev = (ahci_dev_t *)ata_dev;
+
+	if (count == 0)
+		return 0;
+
+	if (ata_dev->read_cmd == ATA_READ_DMA) {
+		if (start >= (1 << 28)) {
+		       printf("ahci: Sector is not 28-bit addressable.\n");
+		       return -1;
+		} else if (count > 256) {
+		       printf("ahci: Sector count too high (max. 256).\n");
+		       count = 256;
+		}
+#ifdef CONFIG_STORAGE_64BIT_LBA
+	} else if (ata_dev->read_cmd == ATA_READ_DMA_EXT) {
+		if (start >= (1ULL << 48)) {
+			printf("ahci: Sector is not 48-bit addressable.\n");
+			return -1;
+		} else if (count > (64 * 1024)) {
+		       printf("ahci: Sector count too high (max. 65536).\n");
+		       count = 64 * 1024;
+		}
+#endif
+	} else {
+		printf("ahci: Unsupported ATA read command (0x%x).\n",
+			ata_dev->read_cmd);
+		return -1;
+	}
+
+	const size_t bytes = count << ata_dev->sector_size_shift;
+	const size_t bytes_feasible = ahci_cmdslot_prepare(dev, buf, bytes, 0);
+	const size_t sectors = bytes_feasible >> ata_dev->sector_size_shift;
+
+	dev->cmdtable->fis[ 0] = FIS_HOST_TO_DEVICE;
+	dev->cmdtable->fis[ 1] = FIS_H2D_CMD;
+	dev->cmdtable->fis[ 2] = ata_dev->read_cmd;
+	dev->cmdtable->fis[ 4] = (start >>  0) & 0xff;
+	dev->cmdtable->fis[ 5] = (start >>  8) & 0xff;
+	dev->cmdtable->fis[ 6] = (start >> 16) & 0xff;
+	dev->cmdtable->fis[ 7] = FIS_H2D_DEV_LBA;
+	dev->cmdtable->fis[ 8] = (start >> 24) & 0xff;
+#ifdef CONFIG_STORAGE_64BIT_LBA
+	if (ata_dev->read_cmd == ATA_READ_DMA_EXT) {
+		dev->cmdtable->fis[ 9] = (start >> 32) & 0xff;
+		dev->cmdtable->fis[10] = (start >> 40) & 0xff;
+	}
+#endif
+	dev->cmdtable->fis[12] = (sectors >>  0) & 0xff;
+	dev->cmdtable->fis[13] = (sectors >>  8) & 0xff;
+
+	if (ahci_cmdslot_exec(dev) < 0)
+		return -1;
+	else
+		return dev->cmdlist->prd_bytes >> ata_dev->sector_size_shift;
+}
diff --git a/payloads/libpayload/drivers/storage/ahci_atapi.c b/payloads/libpayload/drivers/storage/ahci_atapi.c
new file mode 100644
index 0000000000..11305c22c3
--- /dev/null
+++ b/payloads/libpayload/drivers/storage/ahci_atapi.c
@@ -0,0 +1,67 @@
+/*
+ * This file is part of the libpayload project.
+ *
+ * Copyright (C) 2012 secunet Security Networks AG
+ * Copyright (C) 2013 Edward O'Callaghan <eocallaghan@alterapraxis.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <libpayload.h>
+#include <pci.h>
+#include <storage/ata.h>
+#include <storage/ahci.h>
+
+
+#include "ahci_private.h"
+
+
+ssize_t ahci_packet_read_cmd(atapi_dev_t *const _dev,
+				    const u8 *const cmd, const size_t cmdlen,
+				    u8 *const buf, const size_t buflen)
+{
+	ahci_dev_t *const dev = (ahci_dev_t *)_dev;
+
+	if ((cmdlen != 12) && (cmdlen != 16)) {
+		printf("ahci: Only 12- and 16-byte packet commands allowed.\n");
+		return -1;
+	}
+
+	const size_t len = ahci_cmdslot_prepare(dev, buf, buflen, 0);
+	u16 byte_limit = MIN(len, 63 * 1024); /* like Linux */
+	if (byte_limit & 1) ++byte_limit; /* even limit */
+
+	dev->cmdlist[0].cmd |= CMD_ATAPI;
+	dev->cmdtable->fis[0] = FIS_HOST_TO_DEVICE;
+	dev->cmdtable->fis[1] = FIS_H2D_CMD;
+	dev->cmdtable->fis[2] = ATA_PACKET;
+	dev->cmdtable->fis[5] = byte_limit & 0xff;
+	dev->cmdtable->fis[6] = byte_limit >> 8;
+	memcpy((void *)dev->cmdtable->atapi_cmd, cmd, cmdlen);
+
+	return ahci_cmdslot_exec(dev);
+}
diff --git a/payloads/libpayload/drivers/storage/ahci_common.c b/payloads/libpayload/drivers/storage/ahci_common.c
new file mode 100644
index 0000000000..bcb0ce70bc
--- /dev/null
+++ b/payloads/libpayload/drivers/storage/ahci_common.c
@@ -0,0 +1,250 @@
+/*
+ * This file is part of the libpayload project.
+ *
+ * Copyright (C) 2012 secunet Security Networks AG
+ * Copyright (C) 2013 Edward O'Callaghan <eocallaghan@alterapraxis.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <libpayload.h>
+#include <pci.h>
+#include <storage/ata.h>
+#include <storage/ahci.h>
+
+#include "ahci_private.h"
+
+
+#ifdef DEBUG_STATUS
+static inline u32 _ahci_clear_status(volatile u32 *const reg,
+				     const char *const r,
+				     const char *const f)
+{
+	const u32 bits = *reg;
+	if (bits)
+		*reg = bits;
+	printf("ahci: %s: %s == 0x%08x\n", f, r, bits);
+
+	return bits;
+}
+#define ahci_clear_status(p, r) _ahci_clear_status(&(p)->r, #r, __func__)
+#else
+static inline u32 _ahci_clear_status(volatile u32 *const reg)
+{
+	const u32 bits = *reg;
+	if (bits)
+		*reg = bits;
+	return bits;
+}
+#define ahci_clear_status(p, r) _ahci_clear_status(&(p)->r)
+#endif
+
+
+/** Give a buffer with even address. */
+static u8 *ahci_prdbuf_init(ahci_dev_t *const dev,
+			    u8 *const user_buf, const size_t len,
+			    const int out)
+{
+	if ((u32)user_buf & 1) {
+		printf("ahci: Odd buffer pointer (%p).\n", user_buf);
+		if (dev->buf) /* orphaned buffer */
+			free((void *)dev->buf - *(dev->buf - 1));
+		dev->buf = malloc(len + 2);
+		if (!dev->buf)
+			return NULL;
+		dev->user_buf = user_buf;
+		dev->write_back = !out;
+		dev->buflen = len;
+		if ((u32)dev->buf & 1) {
+			dev->buf[0] = 1;
+			dev->buf += 1;
+		} else {
+			dev->buf[0] = 1;
+			dev->buf[1] = 2;
+			dev->buf += 2;
+		}
+		if (out)
+			memcpy(dev->buf, user_buf, len);
+		return dev->buf;
+	} else {
+		return user_buf;
+	}
+}
+
+static void ahci_prdbuf_finalize(ahci_dev_t *const dev)
+{
+	if (dev->buf) {
+		if (dev->write_back)
+			memcpy(dev->user_buf, dev->buf, dev->buflen);
+		free((void *)dev->buf - *(dev->buf - 1));
+	}
+	dev->buf = NULL;
+	dev->user_buf = NULL;
+	dev->write_back = 0;
+	dev->buflen = 0;
+}
+
+int ahci_cmdengine_start(hba_port_t *const port)
+{
+	/* CR has to be clear before starting the command engine.
+	   This shouldn't take too long, but we should time out nevertheless. */
+	int timeout = 1000; /* Time out after 1000 * 1us == 1ms. */
+	while ((port->cmd_stat & HBA_PxCMD_CR) && timeout--)
+		udelay(1);
+	if (timeout < 0) {
+		printf("ahci: Timeout during start of command engine.\n");
+		return 1;
+	}
+
+	port->cmd_stat |= HBA_PxCMD_FRE;
+	port->cmd_stat |= HBA_PxCMD_ST;
+	return 0;
+}
+
+int ahci_cmdengine_stop(hba_port_t *const port)
+{
+	port->cmd_stat &= ~HBA_PxCMD_ST;
+
+	/* Wait for the controller to clear CR.
+	   This shouldn't take too long, but we should time out nevertheless. */
+	int timeout = 1000; /* Time out after 1000 * 1us == 1ms. */
+	while ((port->cmd_stat & HBA_PxCMD_CR) && timeout--)
+		udelay(1);
+	if (timeout < 0) {
+		printf("ahci: Timeout during stopping of command engine.\n");
+		return 1;
+	}
+
+	port->cmd_stat &= ~HBA_PxCMD_FRE;
+
+	/* Wait for the controller to clear FR.
+	   This shouldn't take too long, but we should time out nevertheless. */
+	timeout = 1000; /* Time out after 1000 * 1us == 1ms. */
+	while ((port->cmd_stat & HBA_PxCMD_FR) && timeout--)
+		udelay(1);
+	if (timeout < 0) {
+		printf("ahci: Timeout during stopping of command engine.\n");
+		return 1;
+	}
+
+	return 0;
+}
+
+ssize_t ahci_cmdslot_exec(ahci_dev_t *const dev)
+{
+	const int slotnum = 0; /* We always use the first slot. */
+
+	if (!(dev->port->cmd_stat & HBA_PxCMD_CR))
+		return -1;
+
+	/* Trigger command execution. */
+	dev->port->cmd_issue |= (1 << slotnum);
+
+	/* Wait for the controller to finish command execution. */
+	int timeout = 50000; /* Time out after 50000 * 100us == 5s. */
+	while ((dev->port->cmd_issue & (1 << slotnum)) &&
+			!(dev->port->intr_status & HBA_PxIS_TFES) &&
+			timeout--)
+		udelay(100);
+	if (timeout < 0) {
+		printf("ahci: Timeout during command execution.\n");
+		return -1;
+	}
+
+	ahci_prdbuf_finalize(dev);
+
+	const u32 intr_status = ahci_clear_status(dev->port, intr_status);
+	if (intr_status & (HBA_PxIS_FATAL | HBA_PxIS_PCS)) {
+		ahci_error_recovery(dev, intr_status);
+		return -1;
+	} else {
+		return dev->cmdlist[slotnum].prd_bytes;
+	}
+}
+
+size_t ahci_cmdslot_prepare(ahci_dev_t *const dev,
+				   u8 *const user_buf, size_t buf_len,
+				   const int out)
+{
+	const int slotnum = 0; /* We always use the first slot. */
+
+	size_t read_count = 0;
+
+	memset((void *)&dev->cmdlist[slotnum],
+			'\0', sizeof(dev->cmdlist[slotnum]));
+	memset((void *)dev->cmdtable,
+			'\0', sizeof(*dev->cmdtable));
+	dev->cmdlist[slotnum].cmd = CMD_CFL(FIS_H2D_FIS_LEN);
+	dev->cmdlist[slotnum].cmdtable_base = virt_to_phys(dev->cmdtable);
+
+	if (buf_len > 0) {
+		size_t prdt_len;
+		u8 *buf;
+		int i;
+
+		prdt_len = ((buf_len - 1) >> BYTES_PER_PRD_SHIFT) + 1;
+		const size_t max_prdt_len = ARRAY_SIZE(dev->cmdtable->prdt);
+		if (prdt_len > max_prdt_len) {
+			prdt_len = max_prdt_len;
+			buf_len = prdt_len << BYTES_PER_PRD_SHIFT;
+		}
+
+		dev->cmdlist[slotnum].prdt_length = prdt_len;
+		read_count = buf_len;
+
+		buf = ahci_prdbuf_init(dev, user_buf, buf_len, out);
+		if (!buf)
+			return 0;
+		for (i = 0; i < prdt_len; ++i) {
+			const size_t bytes =
+				(buf_len < BYTES_PER_PRD)
+				? buf_len : BYTES_PER_PRD;
+			dev->cmdtable->prdt[i].data_base = virt_to_phys(buf);
+			dev->cmdtable->prdt[i].flags = PRD_TABLE_BYTES(bytes);
+			buf_len -= bytes;
+			buf += bytes;
+		}
+	}
+
+	return read_count;
+}
+
+int ahci_identify_device(ata_dev_t *const ata_dev, u8 *const buf)
+{
+	ahci_dev_t *const dev = (ahci_dev_t *)ata_dev;
+
+	ahci_cmdslot_prepare(dev, buf, 512, 0);
+
+	dev->cmdtable->fis[0] = FIS_HOST_TO_DEVICE;
+	dev->cmdtable->fis[1] = FIS_H2D_CMD;
+	dev->cmdtable->fis[2] = ata_dev->identify_cmd;
+
+	if ((ahci_cmdslot_exec(dev) < 0) || (dev->cmdlist->prd_bytes != 512))
+		return -1;
+	else
+		return 0;
+}
diff --git a/payloads/libpayload/drivers/storage/ahci_private.h b/payloads/libpayload/drivers/storage/ahci_private.h
index ba1471b5d5..c966133798 100644
--- a/payloads/libpayload/drivers/storage/ahci_private.h
+++ b/payloads/libpayload/drivers/storage/ahci_private.h
@@ -2,6 +2,7 @@
  * This file is part of the libpayload project.
  *
  * Copyright (C) 2012 secunet Security Networks AG
+ * Copyright (C) 2013 Edward O'Callaghan <eocallaghan@alterapraxis.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -198,4 +199,36 @@ typedef struct {
 	size_t buflen;
 } ahci_dev_t;
 
-#endif
+/*
+ * ahci_common.c
+ */
+int ahci_cmdengine_start(hba_port_t *const port);
+
+int ahci_cmdengine_stop(hba_port_t *const port);
+
+ssize_t ahci_cmdslot_exec(ahci_dev_t *const dev);
+
+size_t ahci_cmdslot_prepare(ahci_dev_t *const dev,
+		   u8 *const user_buf, size_t buf_len,
+		   const int out);
+
+int ahci_identify_device(ata_dev_t *const ata_dev, u8 *const buf);
+
+int ahci_error_recovery(ahci_dev_t *const dev, const u32 intr_status);
+
+/*
+ * ahci_atapi.c
+ */
+ssize_t ahci_packet_read_cmd(atapi_dev_t *const _dev,
+		    const u8 *const cmd, const size_t cmdlen,
+		    u8 *const buf, const size_t buflen);
+
+/*
+ * ahci_ata.c
+ */
+ssize_t ahci_ata_read_sectors(ata_dev_t *const ata_dev,
+		     const lba_t start, size_t count,
+		     u8 *const buf);
+
+
+#endif /* _AHCI_PRIVATE_H */