linux-kernel - Re: [PATCH v1 1/1] serial: 8250_dw: Allow hardware flow control to be used

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Message-ID: <1481108989.17976.9.camel@linux.intel.com>
Date:   Wed, 07 Dec 2016 13:09:49 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Jason Uy <jason.uy@...adcom.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>
Cc:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        Noam Camus <noamc@...hip.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Wang Hongcheng <annie.wang@....com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH v1 1/1] serial: 8250_dw: Allow hardware flow control to
 be used

On Tue, 2016-12-06 at 14:34 -0800, Jason Uy wrote:
> In the most common use case, the Synopsys DW UART driver does not
> set the set_termios callback function.  This prevents UPSTAT_AUTOCTS
> from being set when the UART flag CRTSCTS is set.  As a result, the
> driver will use software flow control as opposed to hardware flow
> control.
> 
> To fix the problem, the set_termios callback function is set to the
> DW specific function.  The logic to set UPSTAT_AUTOCTS is moved so
> that any clock error will not affect setting the hardware flow
> control.
> 

It should not affect Intel HW since we are using clock for it (see
drivers/mfd/intel-lpss-pci.c, drivers/acpi/acpi_lpss.c).

Thus, I'm okay with the change.

> Reviewed-by: Scott Branden <scott.branden@...adcom.com>
> Reviewed-by: Ray Jui <ray.jui@...adcom.com>
> Signed-off-by: Jason Uy <jason.uy@...adcom.com>
> ---
>  drivers/tty/serial/8250/8250_dw.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_dw.c
> b/drivers/tty/serial/8250/8250_dw.c
> index 459d726..18f1f8b 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -246,11 +246,11 @@ static void dw8250_set_termios(struct uart_port
> *p, struct ktermios *termios,
>  	if (!ret)
>  		p->uartclk = rate;
>  
> +out:
>  	p->status &= ~UPSTAT_AUTOCTS;
>  	if (termios->c_cflag & CRTSCTS)
>  		p->status |= UPSTAT_AUTOCTS;
>  
> -out:
>  	serial8250_do_set_termios(p, termios, old);
>  }
>  
> @@ -308,13 +308,11 @@ static void dw8250_quirks(struct uart_port *p,
> struct dw8250_data *data)
>  			p->serial_in = dw8250_serial_in32;
>  			data->uart_16550_compatible = true;
>  		}
> -		p->set_termios = dw8250_set_termios;
>  	}
>  
>  	/* Platforms with iDMA */
>  	if (platform_get_resource_byname(to_platform_device(p->dev),
>  					 IORESOURCE_MEM,
> "lpss_priv")) {
> -		p->set_termios = dw8250_set_termios;
>  		data->dma.rx_param = p->dev->parent;
>  		data->dma.tx_param = p->dev->parent;
>  		data->dma.fn = dw8250_idma_filter;
> @@ -392,6 +390,7 @@ static int dw8250_probe(struct platform_device
> *pdev)
>  	p->iotype	= UPIO_MEM;
>  	p->serial_in	= dw8250_serial_in;
>  	p->serial_out	= dw8250_serial_out;
> +	p->set_termios	= dw8250_set_termios;
>  
>  	p->membase = devm_ioremap(dev, regs->start,
> resource_size(regs));
>  	if (!p->membase)

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy