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

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Message-ID: <55a39641-87d4-4f61-11fa-54c8904ac40d@gmail.com>
Date:   Mon, 6 Feb 2017 12:10:34 +0100
From:   Richard Genoud <richard.genoud@...il.com>
To:     Alexandre Belloni <alexandre.belloni@...e-electrons.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
Subject: Re: [PATCH] tty/serial: atmel: ensure state is restored after
 suspending

Hi Alexandre,

On 03/02/2017 23:53, Alexandre Belloni wrote:
> 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;
> +
As struct cache is only used in suspend()/resume() we could add:
#ifdef CONFIG_PM / #endif
to remove it from atmel_uart_port when PM is not selected.
Even if I'm not a big fan of ifdefs, the suspend code is already
compiled out with #ifdef CONFIG_PM, so, at least, it would be consistent.

>  	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);
> 

Thanks !

Richard.