linux-kernel - Re: [PATCH v3] tty: make pl011 serial port driver support 485 mode

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Message-ID: <BEEC2888CE24964AA5C6EAB9EA9DA122272F78@dggemi529-mbs.china.huawei.com>
Date:   Fri, 15 Jan 2021 02:32:39 +0000
From:   zhangqiumiao <zhangqiumiao1@...wei.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "jirislaby@...nel.org" <jirislaby@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "Chenxiang (EulerOS)" <rose.chen@...wei.com>,
        "Yanan (Euler)" <yanan@...wei.com>
Subject: Re: [PATCH v3] tty: make pl011 serial port driver support 485 mode

On Thu, Jan 14, 2021 at 08:28:30PM +0800, zhangqiumiao1@...wei.com wrote:
> From: Qiumiao Zhang <zhangqiumiao1@...wei.com>
> 
> make pl011 serial port support 485 mode full duplex communication
> 
> Signed-off-by: Qiumiao Zhang <zhangqiumiao1@...wei.com>
> ---
> Changes in v3:
>   -Fix busy loop forever in pl011_tx_empty
>   -Move the definition of cr into uart_amba_port
>   -run checkpatch with no error or warning
> 
> Changes in v2:
>   -Fix two compilation errors
> 
>  drivers/tty/serial/amba-pl011.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/drivers/tty/serial/amba-pl011.c 
> b/drivers/tty/serial/amba-pl011.c index c255476..9da10a4 100644
> --- a/drivers/tty/serial/amba-pl011.c
> +++ b/drivers/tty/serial/amba-pl011.c
> @@ -44,6 +44,7 @@
> 
>  #include "amba-pl011.h"
> 
> +#define ISEMPTY			1
>  #define UART_NR			14
> 
>  #define SERIAL_AMBA_MAJOR	204
> @@ -264,6 +265,7 @@ struct uart_amba_port {
>  	unsigned int		fifosize;	/* vendor-specific */
>  	unsigned int		old_cr;		/* state during shutdown */
>  	unsigned int		fixed_baud;	/* vendor-set fixed baud rate */
> +	unsigned int		cr;
>  	char			type[12];
>  #ifdef CONFIG_DMA_ENGINE
>  	/* DMA stuff */
> @@ -1284,6 +1286,8 @@ static inline bool pl011_dma_rx_running(struct uart_amba_port *uap)
>  #define pl011_dma_flush_buffer	NULL
>  #endif
> 
> +static unsigned int pl011_tx_empty(struct uart_port *port);
> +
>  static void pl011_stop_tx(struct uart_port *port)  {
>  	struct uart_amba_port *uap =
> @@ -1292,6 +1296,17 @@ static void pl011_stop_tx(struct uart_port *port)
>  	uap->im &= ~UART011_TXIM;
>  	pl011_write(uap->im, uap, REG_IMSC);
>  	pl011_dma_tx_stop(uap);
> +	if (port->rs485.flags & SER_RS485_ENABLED) {
> +		while(pl011_tx_empty(port) != ISEMPTY) ;

I intend to change this to:
        while(pl011_tx_empty(port) != ISEMPTY)
			cpu_relax();
Is this ok?

> +
> +		uap->cr = pl011_read(uap, REG_CR);
> +		if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND) {
> +			uap->cr |= UART011_CR_RTS;
> +		} else {
> +			uap->cr &= ~UART011_CR_RTS;
> +		}

Checkpatch doesn't find the problem here. Please tell me what's wrong here?

thanks,

Qiumiao Zhang