libata: skip debounce delay on link resume

The link resume logic uses a 200msec delay while debouncing
the SControl register. The rationale behind that delay is
to accommodate some PHYs that behave badly if their SStatus/
SControl registers are pounded immediately on resume.
The Broadcom STB SATA PHY does not seem to have this issue.
This patch introduces a new link flag that allows platforms
to skip the debounce delay if it isn't needed.

Signed-off-by: Danesh Petigara <dpetigara@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

drivers/ata/ahci_brcmstb.c

@@ -85,6 +85,7 @@ struct brcm_ahci_priv {
 
 static const struct ata_port_info ahci_brcm_port_info = {
 	.flags		= AHCI_FLAG_COMMON | ATA_FLAG_NO_DIPM,
+	.link_flags	= ATA_LFLAG_NO_DB_DELAY,
 	.pio_mask	= ATA_PIO4,
 	.udma_mask	= ATA_UDMA6,
 	.port_ops	= &ahci_platform_ops,

drivers/ata/libata-core.c

@@ -3598,7 +3598,8 @@ int sata_link_resume(struct ata_link *link, const unsigned long *params,
 		 * immediately after resuming.  Delay 200ms before
 		 * debouncing.
 		 */
-		ata_msleep(link->ap, 200);
+		if (!(link->flags & ATA_LFLAG_NO_DB_DELAY))
+			ata_msleep(link->ap, 200);
 
 		/* is SControl restored correctly? */
 		if ((rc = sata_scr_read(link, SCR_CONTROL, &scontrol)))

include/linux/libata.h

@@ -205,6 +205,7 @@ enum {
 	ATA_LFLAG_NO_LPM	= (1 << 8), /* disable LPM on this link */
 	ATA_LFLAG_RST_ONCE	= (1 << 9), /* limit recovery to one reset */
 	ATA_LFLAG_CHANGED	= (1 << 10), /* LPM state changed on this link */
+	ATA_LFLAG_NO_DB_DELAY	= (1 << 11), /* no debounce delay on link resume */
 
 	/* struct ata_port flags */
 	ATA_FLAG_SLAVE_POSS	= (1 << 0), /* host supports slave dev */