Re: [PATCH/RFC] serial: Add ioctl to enable auto rs485 mode with some Exar UARTs

[Laurent Pinchart <laurentp@cse-semaphore.com>]

Hi Matthias,

On Friday 19 December 2008 00:48:34 Matthias Fuchs wrote:
> Hi,
>
> please see my patch for enabling the RS485 half-duplex control below.
> Please note that I am using this on a PowerPC platform. So I needed to
> add the ioctl to the PowerPC header. As Wolfgang stated, it is
> already in the x86 header. I am not sure if I have to post the modification
> on the powerpc header to the PowerPC list or if it will be accepted here
> as well.  .... But first I will have to see what you think of this patch
> :-)
>
> Matthias
>
>
> Some Exar UARTs support a auto rs485 mode. In this mode
> the UART's RTS# pin is activated during transmitting and
> can be used to enable a rs485 line driver. This has nothing
> to do with attempts to do this by manually by asserting/
> deasserting handshake lines.

[snip]
> +		serial_outp(up, UART_LCR, 0xbf);
> +		fctr = serial_inp(up, UART_FCTR);
> +		if (rs485ctrl.flags & SER_RS485_ENABLED)
> +			fctr |= 0x08;
> +		else
> +			fctr &= ~0x08;
> +		serial_outp(up, UART_FCTR, fctr);
> +		serial_outp(up, UART_LCR, 0);

You might also want to add a

#define UART_FCTR_RS485	0x08

to include/linux/serial_reg.h instead of using a hardcoded 0x08 constant.

-- 
Laurent Pinchart
CSE Semaphore Belgium

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