linux-kernel - Re: [PATCH] serial: 8250_dw: Fix LCR workaround regression

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Message-ID: <20131211140014.GF28456@xps8300>
Date:	Wed, 11 Dec 2013 16:00:15 +0200
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	James Hogan <james@...anarts.com>
Cc:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Lior Amsalem <alior@...vell.com>,
	Jason Cooper <jason@...edaemon.net>,
	James Hogan <james.hogan@...tec.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Tim Kryger <tim.kryger@...aro.org>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Matt Porter <matt.porter@...aro.org>,
	Markus Mayer <markus.mayer@...aro.org>
Subject: Re: [PATCH] serial: 8250_dw: Fix LCR workaround regression

Hi,

On Tue, Dec 10, 2013 at 10:28:04PM +0000, James Hogan wrote:
> From: James Hogan <james.hogan@...tec.com>
> 
> Commit c49436b657d0 (serial: 8250_dw: Improve unwritable LCR workaround)
> caused a regression. It added a check that the LCR was written properly
> to detect and workaround the busy quirk, but the behaviour of bit 5
> (UART_LCR_SPAR) differs between IP versions 3.00a and 3.14c per the
> docs. On older versions this caused the check to fail and it would
> repeatedly force idle and rewrite the LCR register, causing delays and
> preventing any input from serial being received.
> 
> This is fixed by masking out UART_LCR_SPAR before making the comparison.
> 
> Signed-off-by: James Hogan <james.hogan@...tec.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Jiri Slaby <jslaby@...e.cz>
> Cc: Tim Kryger <tim.kryger@...aro.org>
> Cc: Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
> Cc: Matt Porter <matt.porter@...aro.org>
> Cc: Markus Mayer <markus.mayer@...aro.org>
> Cc: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> Tested-by: Tim Kryger <tim.kryger@...aro.org>
> Tested-by: Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>

I tested this with HW without the busy functionality
(UART_16550_COMPATIBLE == yes). No problems here. FWIW:

Tested-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>


-- 
heikki
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