linux-kernel - Re: [PATCH 2/5] tty/serial: at91: enable peripheral clock before accessing I/O registers

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Date:	Fri, 9 Jan 2015 16:12:47 +0100
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Cyrille Pitchen <cyrille.pitchen@...el.com>,
	<gregkh@...uxfoundation.org>, <wenyou.yang@...el.com>,
	<ludovic.desroches@...el.com>, <leilei.zhao@...el.com>,
	<voice.shen@...el.com>, <josh.wu@...el.com>,
	<linux-serial@...r.kernel.org>
CC:	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/5] tty/serial: at91: enable peripheral clock before
 accessing I/O registers

Le 09/12/2014 14:31, Cyrille Pitchen a écrit :
> atmel_serial_probe() calls atmel_init_port(). In turn, atmel_init_port() calls
> clk_disable_unprepare() to disable the peripheral clock before returning.
> 
> Later atmel_serial_probe() accesses some I/O registers such as the Mode and
> Control registers for RS485 support then the Name and Version registers, through a call to
> atmel_get_ip_name(), but at that moment the peripheral clock was still
> disabled.
> 
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@...el.com>

Acked-by: Nicolas Ferre <nicolas.ferre@...el.com>
and you can add also:
Cc: <stable@...r.kernel.org> # 3.12+

> ---
>  drivers/tty/serial/atmel_serial.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index 756f567..c6621dc 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -2596,6 +2596,12 @@ static int atmel_serial_probe(struct platform_device *pdev)
>  	device_init_wakeup(&pdev->dev, 1);
>  	platform_set_drvdata(pdev, port);
>  
> +	/*
> +	 * The peripheral clock has been disabled by atmel_init_port():
> +	 * enable it before accessing I/O registers
> +	 */
> +	clk_prepare_enable(port->clk);
> +
>  	if (rs485_enabled) {
>  		UART_PUT_MR(&port->uart, ATMEL_US_USMODE_NORMAL);
>  		UART_PUT_CR(&port->uart, ATMEL_US_RTSEN);
> @@ -2606,6 +2612,12 @@ static int atmel_serial_probe(struct platform_device *pdev)
>  	 */
>  	atmel_get_ip_name(&port->uart);
>  
> +	/*
> +	 * The peripheral clock can now safely be disabled till the port
> +	 * is used
> +	 */
> +	clk_disable_unprepare(port->clk);
> +
>  	return 0;
>  
>  err_add_port:
> 


-- 
Nicolas Ferre
--
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