sata_mv: improve warnings about Highpoint RocketRAID 23xx cards

Improve the existing boot/load time warnings from sata_mv
for Highpoint RocketRAID 23xx cards, based on new knowledge
about where the BIOS likes to overwrite sectors with metadata.

Harmless to us, but very useful for end users.
Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/sata_mv.c

@@ -2506,11 +2506,31 @@ static int mv_chip_id(struct ata_host *host, unsigned int board_idx)
 		if (pdev->vendor == PCI_VENDOR_ID_TTI &&
 		    (pdev->device == 0x2300 || pdev->device == 0x2310))
 		{
-			printk(KERN_WARNING "sata_mv: Highpoint RocketRAID BIOS"
-				" will CORRUPT DATA on attached drives when"
-				" configured as \"Legacy\".  BEWARE!\n");
-			printk(KERN_WARNING "sata_mv: Use BIOS \"JBOD\" volumes"
-				" instead for safety.\n");
+			/*
+			 * Highpoint RocketRAID PCIe 23xx series cards:
+			 *
+			 * Unconfigured drives are treated as "Legacy"
+			 * by the BIOS, and it overwrites sector 8 with
+			 * a "Lgcy" metadata block prior to Linux boot.
+			 *
+			 * Configured drives (RAID or JBOD) leave sector 8
+			 * alone, but instead overwrite a high numbered
+			 * sector for the RAID metadata.  This sector can
+			 * be determined exactly, by truncating the physical
+			 * drive capacity to a nice even GB value.
+			 *
+			 * RAID metadata is at: (dev->n_sectors & ~0xfffff)
+			 *
+			 * Warn the user, lest they think we're just buggy.
+			 */
+			printk(KERN_WARNING DRV_NAME ": Highpoint RocketRAID"
+				" BIOS CORRUPTS DATA on all attached drives,"
+				" regardless of if/how they are configured."
+				" BEWARE!\n");
+			printk(KERN_WARNING DRV_NAME ": For data safety, do not"
+				" use sectors 8-9 on \"Legacy\" drives,"
+				" and avoid the final two gigabytes on"
+				" all RocketRAID BIOS initialized drives.\n");
 		}
 	case chip_6042:
 		hpriv->ops = &mv6xxx_ops;