linux-kernel - [PATCH] tty/serial: atmel: ensure state is restored after suspending

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Date:   Fri,  3 Feb 2017 23:53:16 +0100
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Richard Genoud <richard.genoud@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nicolas Ferre <nicolas.ferre@...el.com>,
        linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Subject: [PATCH] tty/serial: atmel: ensure state is restored after suspending

When going to suspend, the UART registers may be lost because the power to
VDDcore is cut. This is not an issue in the normal case but when
no_console_suspend is used, we need to restore the registers in order to
get a functional console.

Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
---
 drivers/tty/serial/atmel_serial.c | 44 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index 168b10cad47b..22e0a73c0cb7 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -175,6 +175,17 @@ struct atmel_uart_port {
 	unsigned int		pending_status;
 	spinlock_t		lock_suspended;
 
+	struct {
+		u32		cr;
+		u32		mr;
+		u32		imr;
+		u32		brgr;
+		u32		rtor;
+		u32		ttgr;
+		u32		fmr;
+		u32		fimr;
+	} cache;
+
 	int (*prepare_rx)(struct uart_port *port);
 	int (*prepare_tx)(struct uart_port *port);
 	void (*schedule_rx)(struct uart_port *port);
@@ -2649,6 +2660,20 @@ static int atmel_serial_suspend(struct platform_device *pdev,
 			cpu_relax();
 	}
 
+	if (atmel_is_console_port(port) && !console_suspend_enabled) {
+		/* Cache register values as we won't get a full shutdown/startup
+		 * cycle
+		 */
+		atmel_port->cache.mr = atmel_uart_readl(port, ATMEL_US_MR);
+		atmel_port->cache.imr = atmel_uart_readl(port, ATMEL_US_IMR);
+		atmel_port->cache.brgr = atmel_uart_readl(port, ATMEL_US_BRGR);
+		atmel_port->cache.rtor = atmel_uart_readl(port,
+							  atmel_port->rtor);
+		atmel_port->cache.ttgr = atmel_uart_readl(port, ATMEL_US_TTGR);
+		atmel_port->cache.fmr = atmel_uart_readl(port, ATMEL_US_FMR);
+		atmel_port->cache.fimr = atmel_uart_readl(port, ATMEL_US_FIMR);
+	}
+
 	/* we can not wake up if we're running on slow clock */
 	atmel_port->may_wakeup = device_may_wakeup(&pdev->dev);
 	if (atmel_serial_clk_will_stop()) {
@@ -2671,6 +2696,25 @@ static int atmel_serial_resume(struct platform_device *pdev)
 	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
 	unsigned long flags;
 
+	if (atmel_is_console_port(port) && !console_suspend_enabled) {
+		atmel_uart_writel(port, ATMEL_US_MR, atmel_port->cache.mr);
+		atmel_uart_writel(port, ATMEL_US_IER, atmel_port->cache.imr);
+		atmel_uart_writel(port, ATMEL_US_BRGR, atmel_port->cache.brgr);
+		atmel_uart_writel(port, atmel_port->rtor,
+				  atmel_port->cache.rtor);
+		atmel_uart_writel(port, ATMEL_US_TTGR, atmel_port->cache.ttgr);
+
+		if (atmel_port->fifo_size) {
+			atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_FIFOEN |
+					  ATMEL_US_RXFCLR | ATMEL_US_TXFLCLR);
+			atmel_uart_writel(port, ATMEL_US_FMR,
+					  atmel_port->cache.fmr);
+			atmel_uart_writel(port, ATMEL_US_FIER,
+					  atmel_port->cache.fimr);
+		}
+		atmel_start_rx(port);
+	}
+
 	spin_lock_irqsave(&atmel_port->lock_suspended, flags);
 	if (atmel_port->pending) {
 		atmel_handle_receive(port, atmel_port->pending);
-- 
2.11.0