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>
diff --git a/payloads/libpayload/drivers/storage/ahci_atapi.c b/payloads/libpayload/drivers/storage/ahci_atapi.c
new file mode 100644
index 0000000..11305c2
--- /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);
+}