usb: musb: dsps: keep VBUS on for host-only mode

Currently VBUS is turned off while a usb device is detached, and turned
on again by the polling routine. This short period VBUS loss prevents
usb modem to switch mode.

VBUS should be constantly on for host-only mode, so this changes the
driver to not turn off VBUS for host-only mode.

Fixes: 2f3fd2c5bde1 ("usb: musb: Prepare dsps glue layer for PM runtime support")
Cc: stable@vger.kernel.org #v4.11
Reported-by: Moreno Bartalucci <moreno.bartalucci@tecnorama.it>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/musb/musb_dsps.c

@@ -245,6 +245,11 @@ static int dsps_check_status(struct musb *musb, void *unused)
 		dsps_mod_timer_optional(glue);
 		break;
 	case OTG_STATE_A_WAIT_BCON:
+		/* keep VBUS on for host-only mode */
+		if (musb->port_mode == MUSB_PORT_MODE_HOST) {
+			dsps_mod_timer_optional(glue);
+			break;
+		}
 		musb_writeb(musb->mregs, MUSB_DEVCTL, 0);
 		skip_session = 1;
 		/* fall */