Revert "tty: serial: OMAP: transmit FIFO threshold interrupts don't wake the chip"

This reverts commit 43cf7c0bebf50d0b68aa42ae6d24cf08e3f24823 as Paul
wants to redo it.

Cc: Paul Walmsley <paul@pwsan.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Govindraj Raja <govindraj.r@ti.com>
Cc: Kevin Hilman <khilman@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

arch/arm/plat-omap/include/plat/omap-serial.h

@@ -131,7 +131,6 @@ struct uart_omap_port {
 	u32			context_loss_cnt;
 	u32			errata;
 	u8			wakeups_enabled;
-	u8			max_tx_count;
 
 	struct pm_qos_request	pm_qos_request;
 	u32			latency;

drivers/tty/serial/omap-serial.c

@@ -88,49 +88,6 @@ static inline void serial_omap_clear_fifos(struct uart_omap_port *up)
 	serial_out(up, UART_FCR, 0);
 }
 
-/**
- * serial_omap_block_cpu_low_power_state - prevent MPU pwrdm from leaving ON
- * @up: struct uart_omap_port *
- *
- * Prevent the MPU powerdomain from entering a power state lower than
- * ON.  (It should be sufficient to prevent it from entering INACTIVE,
- * but there is presently no easy way to do this.)  This works around
- * a suspected silicon bug in the OMAP UART IP blocks.  The UARTs should
- * wake the PRCM when the transmit FIFO threshold interrupt is raised, but
- * they do not.   See also serial_omap_allow_cpu_low_power_state().  No
- * return value.
- */
-static void serial_omap_block_cpu_low_power_state(struct uart_omap_port *up)
-{
-#ifdef CONFIG_CPU_IDLE
-	up->latency = 1;
-	schedule_work(&up->qos_work);
-#else
-	up->max_tx_count = 1;
-#endif
-}
-
-/**
- * serial_omap_allow_cpu_low_power_state - remove power state restriction on MPU
- * @up: struct uart_omap_port *
- *
- * Cancel the effects of serial_omap_block_cpu_low_power_state().
- * This should allow the MPU powerdomain to enter a power state lower
- * than ON, assuming the rest of the kernel is not restricting it.
- * This works around a suspected silicon bug in the OMAP UART IP
- * blocks.  The UARTs should wake the PRCM when the transmit FIFO
- * threshold interrupt is raised, but they do not.  No return value.
- */
-static void serial_omap_allow_cpu_low_power_state(struct uart_omap_port *up)
-{
-#ifdef CONFIG_CPU_IDLE
-	up->latency = up->calc_latency;
-	schedule_work(&up->qos_work);
-#else
-	up->max_tx_count = up->port.fifosize / 4;
-#endif
-}
-
 /*
  * serial_omap_get_divisor - calculate divisor value
  * @port: uart port info
@@ -206,9 +163,6 @@ static void serial_omap_stop_tx(struct uart_port *port)
 		serial_out(up, UART_IER, up->ier);
 	}
 
-	if (!up->use_dma)
-		serial_omap_allow_cpu_low_power_state(up);
-
 	pm_runtime_mark_last_busy(&up->pdev->dev);
 	pm_runtime_put_autosuspend(&up->pdev->dev);
 }
@@ -310,7 +264,7 @@ static void transmit_chars(struct uart_omap_port *up)
 		serial_omap_stop_tx(&up->port);
 		return;
 	}
-	count = up->max_tx_count;
+	count = up->port.fifosize / 4;
 	do {
 		serial_out(up, UART_TX, xmit->buf[xmit->tail]);
 		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
@@ -343,7 +297,6 @@ static void serial_omap_start_tx(struct uart_port *port)
 
 	if (!up->use_dma) {
 		pm_runtime_get_sync(&up->pdev->dev);
-		serial_omap_block_cpu_low_power_state(up);
 		serial_omap_enable_ier_thri(up);
 		pm_runtime_mark_last_busy(&up->pdev->dev);
 		pm_runtime_put_autosuspend(&up->pdev->dev);
@@ -1468,8 +1421,6 @@ static int serial_omap_probe(struct platform_device *pdev)
 	up->port.fifosize = 64;
 	up->port.ops = &serial_omap_pops;
 
-	up->max_tx_count = up->port.fifosize / 4;
-
 	if (pdev->dev.of_node)
 		up->port.line = of_alias_get_id(pdev->dev.of_node, "serial");
 	else