linux-kernel - Re: Possible software flow problem in serial

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Message-ID: <532B891E.80705@hurleysoftware.com>
Date:	Thu, 20 Mar 2014 20:34:38 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	"Bollinger, Seth" <Seth.Bollinger@...i.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-serial <linux-serial@...r.kernel.org>
Subject: Re: Possible software flow problem in serial_core

On 03/20/2014 07:34 PM, Bollinger, Seth wrote:
> Do you have a driver that would be a good example of this?  From looking
> at serial_core.c:uart_start(), is seems that start_tx() is only called if
> the serial_core ring buffer is not empty.  If we don¹t stop the
> transmitter, we slew too many characters.

Yeah, you're right; thanks for catching this.
(I was busy looking at the ll driver and completely missed the bug in
the serial core).

uart_start() should not be conditioning the call to start_tx() on
the ring buffer being empty; ll drivers should already be able to handle
that because CTS flow control change will start_tx regardless of the ring
buffer count.

Will you send a patch?

Regards,
Peter Hurley
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