linux-kernel - Re: [PATCH] synclink fix ldisc buffer argument

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Message-ID: <50BCCD4C.8050209@microgate.com>
Date:	Mon, 03 Dec 2012 10:03:24 -0600
From:	Paul Fulghum <paulkf@...rogate.com>
To:	Chen Gang <gang.chen@...anux.com>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Greg KH <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH] synclink fix ldisc buffer argument

On 12/2/2012 8:20 PM, Chen Gang wrote:
> pardon (I am just learning)
>   does 65535 mean HDLC_MAX_FRAME_SIZE ?
>   why do we need info->max_frame_size >= 4096 ?
> in drivers/tty/synclink_gt.c:
> 3550         if (info->max_frame_size < 4096)
> 3551                 info->max_frame_size = 4096;
> 3552         else if (info->max_frame_size > 65535)
> 3553                 info->max_frame_size = 65535;
> 3554
>  ...
> 3603                 info->max_frame_size = 4096;

The hardware can send and receive HDLC frames up to
64K in size. The driver defaults to 4K max frame size
to save buffer space for the common case
(line 3603 in alloc_dev()).

The module parameter max_frame_size can override the default
in add_device() (lines 3550-3554 are from add_device()
range checking the module parameter)

> if possible:
>   can we move the relative comments (which are inside function) to the
> location just above ldisc_receive_buf ?

The added comment from my first patch described the reuse
of the data buffer as the flag buffer. Alan prefers to use
a zero initialized dummy buffer for the flag buffer argument.
Doing it that way, the comment is not needed.

-- 
Paul Fulghum
MicroGate Systems, Ltd.
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