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

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Date:   Fri, 15 Jan 2021 07:29:12 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     zhangqiumiao <zhangqiumiao1@...wei.com>
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 Fri, Jan 15, 2021 at 02:32:39AM +0000, zhangqiumiao wrote:
> 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?

See other comments on this same list (linux-serial) for a patch for a
different driver a few days ago about why doing that would not be a good
idea.  Did you not review that change when it was submitted?

> > +
> > +		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?

No braces should be needed, have you read the coding style rules?

thanks,

greg k-h