Date:   Fri, 3 Apr 2020 13:53:13 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Hyunki Koo <hyunki00.koo@...sung.com>,
        Kukjin Kim <kgene@...nel.org>, Jiri Slaby <jslaby@...e.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] tty: samsung_tty: 32-bit access for TX/RX hold
 registers

On Fri, Apr 03, 2020 at 01:42:37PM +0200, Greg KH wrote:
> On Fri, Apr 03, 2020 at 08:15:10PM +0900, Hyunki Koo wrote:
> > Support 32-bit access for the TX/RX hold registers UTXH and URXH.
> > 
> > This is required for some newer SoCs.
> > 
> > Signed-off-by: Hyunki Koo <hyunki00.koo@...sung.com>
> > ---
> > v2: 
> > line 954 : change rd_regl to rd_reg in for backward compatibility.
> > line 2031: Add init value for ourport->port.iotype  to UPIO_MEM 
> > v3:
> > line 2031: remove redundant init value  for ourport->port.iotype 
> > v4:
> > correct variable types and change misleading function name
> > ---
> >  drivers/tty/serial/samsung_tty.c | 76 +++++++++++++++++++++++++++++++++-------
> >  1 file changed, 64 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
> > index 73f951d65b93..bdf1d4d12cb1 100644
> > --- a/drivers/tty/serial/samsung_tty.c
> > +++ b/drivers/tty/serial/samsung_tty.c
> > @@ -154,12 +154,47 @@ struct s3c24xx_uart_port {
> >  #define portaddrl(port, reg) \
> >  	((unsigned long *)(unsigned long)((port)->membase + (reg)))
> >  
> > -#define rd_regb(port, reg) (readb_relaxed(portaddr(port, reg)))
> > +static u32 rd_reg(struct uart_port *port, u32 reg)
> > +{
> > +	switch (port->iotype) {
> > +	case UPIO_MEM:
> > +		return readb_relaxed(portaddr(port, reg));
> > +	case UPIO_MEM32:
> > +		return readl_relaxed(portaddr(port, reg));
> > +	default:
> > +		return 0;
> > +	}
> > +	return 0;
> > +}
> > +
> >  #define rd_regl(port, reg) (readl_relaxed(portaddr(port, reg)))
> >  
> > -#define wr_regb(port, reg, val) writeb_relaxed(val, portaddr(port, reg))
> > +static void wr_reg(struct uart_port *port, u32 reg, u32 val)
> > +{
> > +	switch (port->iotype) {
> > +	case UPIO_MEM:
> > +		writeb_relaxed(val, portaddr(port, reg));
> > +		break;
> > +	case UPIO_MEM32:
> > +		writel_relaxed(val, portaddr(port, reg));
> > +		break;
> > +	}
> > +}
> > +
> >  #define wr_regl(port, reg, val) writel_relaxed(val, portaddr(port, reg))
> >  
> > +static void wr_reg_barrier(struct uart_port *port, u32 reg, u32 val)
> > +{
> > +	switch (port->iotype) {
> > +	case UPIO_MEM:
> > +		writeb(val, portaddr(port, reg));
> > +		break;
> > +	case UPIO_MEM32:
> > +		writel(val, portaddr(port, reg));
> > +		break;
> > +	}
> > +}
> 
> why do you have a default for the read function, but not the write
> functions?

The default for read will never happen and it returns bogus value just
to satisfy the compiler. That's my understanding. What would you like to
do for writes()? Print error msg? No point, it should not happen because
of check in probe().

> 
> > +
> >  /* Byte-order aware bit setting/clearing functions. */
> >  
> >  static inline void s3c24xx_set_bit(struct uart_port *port, int idx,
> > @@ -714,7 +749,7 @@ static void s3c24xx_serial_rx_drain_fifo(struct s3c24xx_uart_port *ourport)
> >  		fifocnt--;
> >  
> >  		uerstat = rd_regl(port, S3C2410_UERSTAT);
> > -		ch = rd_regb(port, S3C2410_URXH);
> > +		ch = rd_reg(port, S3C2410_URXH);
> >  
> >  		if (port->flags & UPF_CONS_FLOW) {
> >  			int txe = s3c24xx_serial_txempty_nofifo(port);
> > @@ -826,7 +861,7 @@ static irqreturn_t s3c24xx_serial_tx_chars(int irq, void *id)
> >  	}
> >  
> >  	if (port->x_char) {
> > -		wr_regb(port, S3C2410_UTXH, port->x_char);
> > +		wr_reg(port, S3C2410_UTXH, port->x_char);
> >  		port->icount.tx++;
> >  		port->x_char = 0;
> >  		goto out;
> > @@ -852,7 +887,7 @@ static irqreturn_t s3c24xx_serial_tx_chars(int irq, void *id)
> >  		if (rd_regl(port, S3C2410_UFSTAT) & ourport->info->tx_fifofull)
> >  			break;
> >  
> > -		wr_regb(port, S3C2410_UTXH, xmit->buf[xmit->tail]);
> > +		wr_reg(port, S3C2410_UTXH, xmit->buf[xmit->tail]);
> >  		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
> >  		port->icount.tx++;
> >  		count--;
> > @@ -916,7 +951,7 @@ static unsigned int s3c24xx_serial_tx_empty(struct uart_port *port)
> >  /* no modem control lines */
> >  static unsigned int s3c24xx_serial_get_mctrl(struct uart_port *port)
> >  {
> > -	unsigned int umstat = rd_regb(port, S3C2410_UMSTAT);
> > +	unsigned int umstat = rd_reg(port, S3C2410_UMSTAT);
> >  
> >  	if (umstat & S3C2410_UMSTAT_CTS)
> >  		return TIOCM_CAR | TIOCM_DSR | TIOCM_CTS;
> > @@ -1974,7 +2009,7 @@ static int s3c24xx_serial_probe(struct platform_device *pdev)
> >  	struct device_node *np = pdev->dev.of_node;
> >  	struct s3c24xx_uart_port *ourport;
> >  	int index = probe_index;
> > -	int ret;
> > +	int ret, prop = 0;
> >  
> >  	if (np) {
> >  		ret = of_alias_get_id(np, "serial");
> > @@ -2000,10 +2035,27 @@ static int s3c24xx_serial_probe(struct platform_device *pdev)
> >  			dev_get_platdata(&pdev->dev) :
> >  			ourport->drv_data->def_cfg;
> >  
> > -	if (np)
> > +	if (np) {
> >  		of_property_read_u32(np,
> >  			"samsung,uart-fifosize", &ourport->port.fifosize);
> >  
> > +		if (of_property_read_u32(np, "reg-io-width", &prop) == 0) {
> > +			switch (prop) {
> > +			case 1:
> > +				ourport->port.iotype = UPIO_MEM;
> > +				break;
> > +			case 4:
> > +				ourport->port.iotype = UPIO_MEM32;
> > +				break;
> > +			default:
> > +				dev_warn(&pdev->dev, "unsupported reg-io-width (%d)\n",
> > +						prop);
> > +				ret = -EINVAL;
> > +				break;
> > +			}
> > +		}
> > +	}
> 
> If the property is not there, the type will be uninitialized and no
> warning will be spit out, are you sure you want to do that?

The default value from initial ourport will be used, which is UPIO_MEM.
This way it is backward compatible.

Best regards,
Krzysztof

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