linux-kernel - Re: [PATCH V2 5/5] usb: serial: f81534: fix tx error on some baud rate

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Date:   Tue, 9 Jan 2018 12:32:16 +0100
From:   Johan Hovold <johan@...nel.org>
To:     "Ji-Ze Hong (Peter Hong)" <hpeter@...il.com>
Cc:     johan@...nel.org, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        peter_hong@...tek.com.tw,
        "Ji-Ze Hong (Peter Hong)" <hpeter+linux_kernel@...il.com>
Subject: Re: [PATCH V2 5/5] usb: serial: f81534: fix tx error on some baud
 rate

On Thu, Jan 04, 2018 at 10:29:21AM +0800, Ji-Ze Hong (Peter Hong) wrote:
> The F81532/534 had 4 clocksource 1.846/18.46/14.77/24MHz and baud rates
> can be up to 1.5Mbits with 24MHz. But on some baud rate (384~500kps), the
> TX side will send the data frame too close to treat frame error on RX
> side. This patch will force all TX data frame with delay 1bit gap.
> 
> Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_kernel@...il.com>
> ---
> V2:
> 	1: First introduced in this series patches.
> 
>  drivers/usb/serial/f81534.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/usb/serial/f81534.c b/drivers/usb/serial/f81534.c
> index a4666171239a..513805eeae6a 100644
> --- a/drivers/usb/serial/f81534.c
> +++ b/drivers/usb/serial/f81534.c
> @@ -130,6 +130,7 @@
>  #define F81534_CLK_18_46_MHZ		(F81534_UART_EN | BIT(1))
>  #define F81534_CLK_24_MHZ		(F81534_UART_EN | BIT(2))
>  #define F81534_CLK_14_77_MHZ		(F81534_UART_EN | BIT(1) | BIT(2))
> +#define F81534_CLK_TX_DELAY_1BIT	BIT(3)
>  
>  #define F81534_CLK_RS485_MODE		BIT(4)
>  #define F81534_CLK_RS485_INVERT		BIT(5)
> @@ -1438,6 +1439,11 @@ static int f81534_port_probe(struct usb_serial_port *port)
>  		break;
>  	}
>  
> +	/*
> +	 * We'll make tx frame error when baud rate from 384~500kps. So we'll
> +	 * delay all tx data frame with 1bit.
> +	 */
> +	port_priv->shadow_clk |= F81534_CLK_TX_DELAY_1BIT;

You don't wan't to enable this only for the affected rates?

>  	return f81534_set_port_output_pin(port);
>  }

Johan