linux-kernel - Re: [PATCH] Combine two one-character CR-LF writes into one two-character write for O

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Message-ID: <20090813195554.GA22751@cuplxvomd02.corp.sa.net>
Date:	Thu, 13 Aug 2009 12:55:54 -0700
From:	David VomLehn <dvomlehn@...co.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org, greg@...ah.com,
	linux-usb@...r.kernel.org
Subject: Re: [PATCH] Combine two one-character CR-LF writes into one
	two-character write for O_ONLCR

On Thu, Aug 13, 2009 at 08:50:18PM +0100, Alan Cox wrote:
> > do_output_char() function uses the struct tty_operations function write_room()
> > to determine whether it is possible to write two characters. It uses
> > tty_put_char() for each character which, for the USB generic serial driver,
> > translates into a write() for each character. For the USB generic serial
> > driver the value returned by write_room() only applies to the next write().
> 
> The USB serial driver is broken, fix it instead. It's not even hard to
> fix.
> 
> > +			tty->ops->write(tty, crlf, ARRAY_SIZE(crlf));
> > +			return ARRAY_SIZE(crlf);
> 
> Emphatic NAK. Someone needs to actually fix the broken USB drivers for
> once. This is just one example of where the device will go kersplat if its
> broken, others include things like losing flow control.

Works for me; please consider the patch withdrawn. I'll take a crack at fixing
the generic serial driver the right way; if other drivers are doing mix-and-match
with per-device code and generic code, they could get broken. I have no way to
test for this, so I'm hoping others will help out.

David VL
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