linux-kernel - Re: [PATCH V2 2/3] tty: serial: fsl_lpuart: remove RTS/CTS control from set/get

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Date:	Mon, 8 Jun 2015 12:55:45 +0530
From:	Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
CC:	<gregkh@...uxfoundation.org>, <devicetree@...r.kernel.org>,
	<linux-serial@...r.kernel.org>, <moorray3@...pl>,
	<linux-kernel@...r.kernel.org>, <stefan@...er.ch>,
	<bhuvanchandra.dv@...il.com>, <kernel@...gutronix.de>,
	<shawn.guo@...aro.org>, <jslaby@...e.cz>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH V2 2/3] tty: serial: fsl_lpuart: remove RTS/CTS control
 from set/get_mctrl

Hello,

On 06/08/2015 12:11 PM, Uwe Kleine-König wrote:
> Hello,
>
> On Mon, Jun 01, 2015 at 10:51:06AM +0530, Bhuvanchandra DV wrote:
>> The LPUART does not provide manual control of RTS/CTS signals,
>> those can only be controlled by the hardware directly. Therefore
>> manual control of those signals through mctrl can not be provided.
>> The current implementation enables/disables the automatic control,
>> which is not what mctrl should do, hence remove the incorrect
>> implementation.
>>
>> Signed-off-by: Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>
>> ---
>>   drivers/tty/serial/fsl_lpuart.c | 63 +++++------------------------------------
>>   1 file changed, 7 insertions(+), 56 deletions(-)
>>
>> diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
>> index 08ce76f..532cfb7 100644
>> --- a/drivers/tty/serial/fsl_lpuart.c
>> +++ b/drivers/tty/serial/fsl_lpuart.c
>> @@ -822,64 +822,15 @@ static unsigned int lpuart32_tx_empty(struct uart_port *port)
>>
>>   static unsigned int lpuart_get_mctrl(struct uart_port *port)
>>   {
>> -	unsigned int temp = 0;
>> -	unsigned char reg;
>> -
>> -	reg = readb(port->membase + UARTMODEM);
>> -	if (reg & UARTMODEM_TXCTSE)
>> -		temp |= TIOCM_CTS;
>> -
>> -	if (reg & UARTMODEM_RXRTSE)
>> -		temp |= TIOCM_RTS;
>> -
>> -	return temp;
>  From reading the commit log I would expect that you only touch the
> set_mctrl function, but not get_mctrl. Assuming your code change is
> right, can you mention this in the commit log please? The bits
> UARTMODEM_TXCTSE and UARTMODEM_RXRTSE only control the automatic mode?
OK, will use 'get/set_mctrl' instead of 'mctrl' in the commit log.
Yes, those bits are only responsible for enabling/disabling the auto 
hardware flow control, not for controlling the RTS/CTS signals directly.
>
> What is the problem you're fixing here? I'm not sure how such an UART
> should be handled, but I imagine that you want to make use of automatic
> mode in some cases. Greg?
>
Fixing the implementation of hardware flow control wrt LPUART hardware.
> Best regards
> Uwe
>

Best regards,
Bhuvan
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