linux-kernel - Re: [PATCH 2/3] USB : serial : invoke dcd

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Date:	Fri, 13 Sep 2013 23:12:41 +0400
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Paul Chavent <Paul.Chavent@...ra.fr>
CC:	linux-usb@...r.kernel.org, gregkh@...uxfoundation.org,
	jhovold@...il.com, fschaefer.oss@...glemail.com, jslaby@...e.cz,
	max@...e.de, giometti@...eenne.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] USB : serial : invoke dcd_change ldisc's handler.

Hello.

On 09/13/2013 07:35 PM, Paul Chavent wrote:

> Signed-off-by: Paul Chavent <paul.chavent@...ra.fr>
> ---
>   Documentation/pps/pps.txt    | 15 +++++++++++++++
>   drivers/usb/serial/generic.c |  9 +++++++++
>   2 files changed, 24 insertions(+)

> diff --git a/Documentation/pps/pps.txt b/Documentation/pps/pps.txt
> index d35dcdd..67b9a94 100644
> --- a/Documentation/pps/pps.txt
> +++ b/Documentation/pps/pps.txt
> @@ -66,6 +66,21 @@ In LinuxPPS the PPS sources are simply char devices usually mapped
>   into files /dev/pps0, /dev/pps1, etc..
>
>
> +PPS with USB to serial devices
> +------------------------------
> +
> +It is possible to grab the PPS from an USB to serial device. However,
> +you should take into account the latencies and jitter introduced by
> +the USB stack. Users has reported clock instability around +-1ms when
> +synchronized with PPS through USB. This isn't suited for time server
> +synchronisation.

    Thunderbird spellchecker underlines this word -- "synchronization" is 
probably better.

[...]
> diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
> index 1f31e6b..877d6e0 100644
> --- a/drivers/usb/serial/generic.c
> +++ b/drivers/usb/serial/generic.c
> @@ -568,6 +568,15 @@ void usb_serial_handle_dcd_change(struct usb_serial_port *usb_port,
>   {
>   	struct tty_port *port = &usb_port->port;
>
> +	if (tty) {
> +		struct tty_ldisc *ld = tty_ldisc_ref(tty);

    Insert an empty line after declaration as above -- keep the style 
consistent, please.

> +		if (ld) {
> +			if (ld->ops->dcd_change)
> +				ld->ops->dcd_change(tty, status);
> +			tty_ldisc_deref(ld);
> +		}
> +	}
> +

WBR, Sergei

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