[PATCH] libata: implement presence detection via polling IDENTIFY

On some controllers (ICHs in piix mode), there is *NO* reliable way to
determine device presence other than issuing IDENTIFY and see how the
transaction proceeds by watching the TF status register.

libata acted this way before irq-pio and phantom devices caused very
little problem but now that IDENTIFY is performed using IRQ drive PIO,
such phantom devices now result in multiple 30sec timeouts during
boot.

This patch implements ATA_FLAG_DETECT_POLLING.  If a LLD sets this
flag, libata core issues the initial IDENTIFY in polling mode and if
the initial data transfer fails w/ HSM violation, the port is
considered to be empty thus replicating the old libata and IDE
behavior.

Signed-off-by: Jeff Garzik <jeff@garzik.org>

include/linux/libata.h

@@ -176,6 +176,8 @@ enum {
 	ATA_FLAG_SKIP_D2H_BSY	= (1 << 12), /* can't wait for the first D2H
 					      * Register FIS clearing BSY */
 	ATA_FLAG_DEBUGMSG	= (1 << 13),
+	ATA_FLAG_DETECT_POLLING	= (1 << 14), /* detect device presence by
+					      * polling IDENTIFY */
 
 	/* The following flag belongs to ap->pflags but is kept in
 	 * ap->flags because it's referenced in many LLDs and will be
@@ -335,6 +337,7 @@ enum ata_completion_errors {
 	AC_ERR_SYSTEM		= (1 << 6), /* system error */
 	AC_ERR_INVALID		= (1 << 7), /* invalid argument */
 	AC_ERR_OTHER		= (1 << 8), /* unknown */
+	AC_ERR_NODEV_HINT	= (1 << 9), /* polling device detection hint */
 };
 
 /* forward declarations */