linux-kernel - Re: [PATCH v4] tty: make pl011 serial port driver support 485 mode

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Date:   Thu, 4 Feb 2021 16:51:33 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     zhangqiumiao1@...wei.com
Cc:     jirislaby@...nel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH v4] tty: make pl011 serial port driver support 485 mode

On Mon, Feb 01, 2021 at 03:30:43PM +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 v4:
>   -Add a bound to the loop in pl011_stop_tx
>   -Remove extra curly braces in pl011_stop_tx
> 
> 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 | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> index c255476..026add3 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 */
> @@ -1284,14 +1286,33 @@ 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)
>  {
> +	unsigned int count = 1000000;    /* 1s */

1 second of what?

>  	struct uart_amba_port *uap =
>  	    container_of(port, struct uart_amba_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 && count) {
> +			count--;
> +			cpu_relax();
> +			udelay(1);

Why relax and delay?

And always run checkpatch on your change before sending it out next
time.

thanks,

greg k-h