From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 14 Sep 2023 20:43:24 +0206
Subject: [PATCH 007/134] serial: 8250_dma: Use port lock wrappers
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz

When a serial port is used for kernel console output, then all
modifications to the UART registers which are done from other contexts,
e.g. getty, termios, are interference points for the kernel console.

So far this has been ignored and the printk output is based on the
principle of hope. The rework of the console infrastructure which aims to
support threaded and atomic consoles, requires to mark sections which
modify the UART registers as unsafe. This allows the atomic write function
to make informed decisions and eventually to restore operational state. It
also allows to prevent the regular UART code from modifying UART registers
while printk output is in progress.

All modifications of UART registers are guarded by the UART port lock,
which provides an obvious synchronization point with the console
infrastructure.

To avoid adding this functionality to all UART drivers, wrap the
spin_[un]lock*() invocations for uart_port::lock into helper functions
which just contain the spin_[un]lock*() invocations for now. In a
subsequent step these helpers will gain the console synchronization
mechanisms.

Converted with coccinelle. No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Link: https://lore.kernel.org/r/20230914183831.587273-8-john.ogness@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/tty/serial/8250/8250_dma.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/tty/serial/8250/8250_dma.c
+++ b/drivers/tty/serial/8250/8250_dma.c
@@ -22,7 +22,7 @@ static void __dma_tx_complete(void *para
 	dma_sync_single_for_cpu(dma->txchan->device->dev, dma->tx_addr,
 				UART_XMIT_SIZE, DMA_TO_DEVICE);
 
-	spin_lock_irqsave(&p->port.lock, flags);
+	uart_port_lock_irqsave(&p->port, &flags);
 
 	dma->tx_running = 0;
 
@@ -35,7 +35,7 @@ static void __dma_tx_complete(void *para
 	if (ret || !dma->tx_running)
 		serial8250_set_THRI(p);
 
-	spin_unlock_irqrestore(&p->port.lock, flags);
+	uart_port_unlock_irqrestore(&p->port, flags);
 }
 
 static void __dma_rx_complete(struct uart_8250_port *p)
@@ -70,7 +70,7 @@ static void dma_rx_complete(void *param)
 	struct uart_8250_dma *dma = p->dma;
 	unsigned long flags;
 
-	spin_lock_irqsave(&p->port.lock, flags);
+	uart_port_lock_irqsave(&p->port, &flags);
 	if (dma->rx_running)
 		__dma_rx_complete(p);
 
@@ -80,7 +80,7 @@ static void dma_rx_complete(void *param)
 	 */
 	if (!dma->rx_running && (serial_lsr_in(p) & UART_LSR_DR))
 		p->dma->rx_dma(p);
-	spin_unlock_irqrestore(&p->port.lock, flags);
+	uart_port_unlock_irqrestore(&p->port, flags);
 }
 
 int serial8250_tx_dma(struct uart_8250_port *p)
