Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 7 Jun 2018 09:56:33 +0200
From:   Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= 
        <u.kleine-koenig@pengutronix.de>
To:     Stefan Agner <stefan@agner.ch>
Cc:     gregkh@linuxfoundation.org, festevam@gmail.com, jslaby@suse.com,
        linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] serial: imx: fix cached UCR2 read on software reset
Message-ID: <20180607075633.y3tm245jv7nkdrqx@pengutronix.de>
References: <20180420124407.12892-1-stefan@agner.ch>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20180420124407.12892-1-stefan@agner.ch>
User-Agent: NeoMutt/20170113 (1.7.2)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Apr 20, 2018 at 02:44:07PM +0200, Stefan Agner wrote:
> To reset the UART the SRST needs be cleared (low active). According
> to the documentation the bit will remain active for 4 module clocks
> until it is cleared (set to 1).
> 
> Hence the real register need to be read in case the cached register
> indicates that the SRST bit is zero.
> 
> This bug lead to wrong baudrate because the baud rate register got
> restored before reset completed in imx_flush_buffer.
> 
> Fixes: 3a0ab62f43de ("serial: imx: implement shadow registers for UCRx and UFCR")
> Signed-off-by: Stefan Agner <stefan@agner.ch>
> Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
> Reviewed-by: Uwe Kleine-K?nig <u.kleine-koenig@pengutronix.de>

For the record, there is a customer of mine who reports that this commit
breaks rs485 communication on i.MX25 because RTS stops to toggle as
intended.

(Some details: uart3, fsl,uart-has-rtscts, fsl,dte-mode,
linux,rs485-enabled-at-boot-time, native RTS.)

I didn't debug this yet.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |