linux-kernel - Re: [PATCH] serial: 8250: Do XR17V35X specific wakeup in serial8250_do

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Date:	Fri, 19 Jun 2015 12:09:10 -0500
From:	Michael Welling <mwelling@...e.org>
To:	Joerg Roedel <joro@...tes.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, Joerg Roedel <jroedel@...e.de>,
	Peter Hurley <peter@...leysoftware.com>,
	Joe Schultz <jschultz@...-inc.com>
Subject: Re: [PATCH] serial: 8250: Do XR17V35X specific wakeup in
 serial8250_do_startup

On Fri, Jun 19, 2015 at 05:12:17PM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
> 
> While debugging why my 8-port XR17V35X card does not work
> with the in-kernel serial driver, I found that some chip
> specific wakeup code is necessary to get it working.
> 
> Specificly the EFR_ECB bit needs to be set in the
> chip-specific UART_XR_EFR register, so that writing to a
> couple of other configuration bits is enabled.
> 
> Cc: Peter Hurley <peter@...leysoftware.com>
> Cc: Michael Welling <mwelling@...e.org>
> Cc: Joe Schultz <jschultz@...-inc.com>
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
>  drivers/tty/serial/8250/8250_core.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index 4506e40..de34db3 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -2176,6 +2176,18 @@ int serial8250_do_startup(struct uart_port *port)
>  	 */
>  	enable_rsa(up);
>  #endif
> +
> +	/*
> +	 * Do this right before clearing the FIFOs to prevent
> +	 * interrupt storm.
> +	 */
> +	if (port->type == PORT_XR17V35X) {
> +		/* Wake up and initialize UART */
> +		serial_port_out(port, UART_XR_EFR, UART_EFR_ECB);
> +		serial_port_out(port, UART_IER, 0);
> +		serial_port_out(port, UART_LCR, 0);
> +	}
> +

Looks good to me. The datasheet indicates that bit 4 of the EFR needs to be set to access
to IER [7:5], ISR [5:4], FCR[5:4], MCR[7:5], MSR.

>  	/*
>  	 * Clear the FIFO buffers and disable them.
>  	 * (they will be reenabled in set_termios())
> -- 
> 1.8.4.5
> 
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