Date: Thu, 21 Sep 2017 20:20:17 +0200
From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= 
        <u.kleine-koenig@pengutronix.de>
To: Martyn Welch <martyn.welch@collabora.co.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Nandor Han <nandor.han@ge.com>,
        Romain Perier <romain.perier@collabora.com>,
        linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, Fabio Estevam <fabio.estevam@nxp.com>
Subject: Re: [PATCH v3 1/6] serial: imx: remove CTSC and CTS handling from
 imx_disable_dma
Message-ID: <20170921182017.t7c75tyy66q7q3ns@pengutronix.de>
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On Thu, Sep 21, 2017 at 05:18:12PM +0100, Martyn Welch wrote:
> From: Nandor Han <nandor.han@ge.com>
> 
> The CTSC and CTS bits affect operation of the CTS/RTS hardware flow
> control signal (depending on whether the device is in DCE or DTE mode) and
> are not related to DMA. When in RS-232 mode, the driver is using the
> automatic CTSC control based on a rxFIFO fill level unless the state of
> the CTS signal is explictly set via an ioctl call.
> 
> Previous improvements to the imx serial driver have resulted on
> imx_disable_dma() only being called on shutdown, by which point the
> serial core has already correctly deasserted CTS.
> 
> Testing shows that without this handling in imx_disable_dma() the CTS
> signal state is set correctly when the device is open and TIOCM_RTS is
> set/cleared via the TIOCMGET ioctl. The CTS signal is also correctly
> deasserted when the device file is closed.

With that block kept CTS set once more to inactive. So the block doesn't
hurt and is "only" superflous, right?

> When in RS-485 mode, the driver uses the CTS signal very differently and
> appears to control it via calls to imx_port_rts_active() and
> imx_port_rts_inactive().
> 
> This configuration of the CTSC and CTS bits are therefore not needed.
> 
> Signed-off-by: Nandor Han <nandor.han@ge.com>
> Signed-off-by: Romain Perier <romain.perier@collabora.com>
> Signed-off-by: Martyn Welch <martyn.welch@collabora.co.uk>
> ---
>  drivers/tty/serial/imx.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index fe368a4..d90dae3 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -1225,11 +1225,6 @@ static void imx_disable_dma(struct imx_port *sport)
>  	temp &= ~(UCR1_RDMAEN | UCR1_TDMAEN | UCR1_ATDMAEN);
>  	writel(temp, sport->port.membase + UCR1);
>  
> -	/* clear UCR2 */
> -	temp = readl(sport->port.membase + UCR2);
> -	temp &= ~(UCR2_CTSC | UCR2_CTS | UCR2_ATEN);
> -	writel(temp, sport->port.membase + UCR2);

The commit log doesn't mention ATEN, I guess that one just doesn't
matter any more at this stage? Would be nice to point out though.

Best regards
Uwe

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