Merge tag 'tty-7.0-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

Pull tty/serial fixes from Greg KH:
 "Here are some small tty/vt and serial driver fixes for 7.0-rc5.
  Included in here are:

   - 8250 driver fixes for reported problems

   - serial core lockup fix

   - uartlite driver bugfix

   - vt save/restore bugfix

  All of these have been in linux-next for over a week with no reported
  problems"

* tag 'tty-7.0-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty:
  vt: save/restore unicode screen buffer for alternate screen
  serial: 8250_dw: Ensure BUSY is deasserted
  serial: 8250: Add late synchronize_irq() to shutdown to handle DW UART BUSY
  serial: 8250_dw: Rework IIR_NO_INT handling to stop interrupt storm
  serial: 8250_dw: Rework dw8250_handle_irq() locking and IIR handling
  serial: 8250: Add serial8250_handle_irq_locked()
  serial: 8250_dw: Avoid unnecessary LCR writes
  serial: 8250: Protect LCR write in shutdown
  serial: 8250_pci: add support for the AX99100
  serial: core: fix infinite loop in handle_tx() for PORT_UNKNOWN
  serial: uartlite: fix PM runtime usage count underflow on probe
  serial: 8250: always disable IRQ during THRE test
  serial: 8250: Fix TX deadlock when using DMA

Author: torvalds

drivers/tty/serial/8250/8250.h

@@ -175,7 +175,9 @@ static unsigned int __maybe_unused serial_icr_read(struct uart_8250_port *up,
 	return value;
 }
 
+void serial8250_clear_fifos(struct uart_8250_port *p);
 void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p);
+void serial8250_fifo_wait_for_lsr_thre(struct uart_8250_port *up, unsigned int count);
 
 void serial8250_rpm_get(struct uart_8250_port *p);
 void serial8250_rpm_put(struct uart_8250_port *p);
@@ -400,6 +402,26 @@ static inline bool serial8250_tx_dma_running(struct uart_8250_port *p)
 
 	return dma && dma->tx_running;
 }
+
+static inline void serial8250_tx_dma_pause(struct uart_8250_port *p)
+{
+	struct uart_8250_dma *dma = p->dma;
+
+	if (!dma->tx_running)
+		return;
+
+	dmaengine_pause(dma->txchan);
+}
+
+static inline void serial8250_tx_dma_resume(struct uart_8250_port *p)
+{
+	struct uart_8250_dma *dma = p->dma;
+
+	if (!dma->tx_running)
+		return;
+
+	dmaengine_resume(dma->txchan);
+}
 #else
 static inline int serial8250_tx_dma(struct uart_8250_port *p)
 {
@@ -421,6 +443,9 @@ static inline bool serial8250_tx_dma_running(struct uart_8250_port *p)
 {
 	return false;
 }
+
+static inline void serial8250_tx_dma_pause(struct uart_8250_port *p) { }
+static inline void serial8250_tx_dma_resume(struct uart_8250_port *p) { }
 #endif
 
 static inline int ns16550a_goto_highspeed(struct uart_8250_port *up)

drivers/tty/serial/8250/8250_dma.c

@@ -162,7 +162,22 @@ void serial8250_tx_dma_flush(struct uart_8250_port *p)
 	 */
 	dma->tx_size = 0;
 
+	/*
+	 * We can't use `dmaengine_terminate_sync` because `uart_flush_buffer` is
+	 * holding the uart port spinlock.
+	 */
 	dmaengine_terminate_async(dma->txchan);
+
+	/*
+	 * The callback might or might not run. If it doesn't run, we need to ensure
+	 * that `tx_running` is cleared so that we can schedule new transactions.
+	 * If it does run, then the zombie callback will clear `tx_running` again
+	 * and perform a no-op since `tx_size` was cleared above.
+	 *
+	 * In either case, we ASSUME the DMA transaction will terminate before we
+	 * issue a new `serial8250_tx_dma`.
+	 */
+	dma->tx_running = 0;
 }
 
 int serial8250_rx_dma(struct uart_8250_port *p)