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List:       linux-serial
Subject:    Re: [PATCH] serial: 8250_dw: Fix LCR workaround regression
From:       Heikki Krogerus <heikki.krogerus () linux ! intel ! com>
Date:       2013-12-11 14:00:15
Message-ID: 20131211140014.GF28456 () xps8300
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Hi,

On Tue, Dec 10, 2013 at 10:28:04PM +0000, James Hogan wrote:
> From: James Hogan <james.hogan@imgtec.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@imgtec.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Jiri Slaby <jslaby@suse.cz>
> Cc: Tim Kryger <tim.kryger@linaro.org>
> Cc: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
> Cc: Matt Porter <matt.porter@linaro.org>
> Cc: Markus Mayer <markus.mayer@linaro.org>
> Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> Tested-by: Tim Kryger <tim.kryger@linaro.org>
> Tested-by: Ezequiel Garcia <ezequiel.garcia@free-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@linux.intel.com>


-- 
heikki
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