Message-ID: <55ACE8D3.5070201@atmel.com>
Date:	Mon, 20 Jul 2015 14:25:55 +0200
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Cyrille Pitchen <cyrille.pitchen@...el.com>,
	<gregkh@...uxfoundation.org>, <wenyou.yang@...el.com>,
	<ludovic.desroches@...el.com>, <leilei.zhao@...el.com>,
	<josh.wu@...el.com>, <alexandre.belloni@...e-electrons.com>,
	<linux-serial@...r.kernel.org>
CC:	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<devicetree@...r.kernel.org>, <galak@...eaurora.org>,
	<ijc+devicetree@...lion.org.uk>, <mark.rutland@....com>,
	<pawel.moll@....com>, <robh+dt@...nel.org>
Subject: Re: [PATCH v4 4/5] tty/serial: at91: add support to FIFOs

Le 02/07/2015 15:18, Cyrille Pitchen a écrit :
> Depending on the hardware, TX and RX FIFOs may be available. The RX
> FIFO can avoid receive overruns, especially when DMA transfers are
> not used to read data from the Receive Holding Register. For heavy
> system load, The CPU is likely not be able to fetch data fast enough
> from the RHR.
> 
> In addition, the RX FIFO can supersede the DMA/PDC to control the RTS
> line when the Hardware Handshaking mode is enabled. Two thresholds
> are to be set for that purpose:
> - When the number of data in the RX FIFO crosses and becomes lower
>   than or equal to the low threshold, the RTS line is set to low
>   level: the remote peer is requested to send data.
> - When the number of data in the RX FIFO crosses and becomes greater
>   than or equal to the high threshold, the RTS line is set to high
>   level: the remote peer should stop sending new data.
> - low threshold <= high threshold
> Once these two thresholds are set properly, this new feature is
> enabled by setting the FIFO RTS Control bit of the FIFO Mode Register.
> 
> FIFOs also introduce a new multiple data mode: the USART works either
> in multiple data mode or in single data (legacy) mode.
> 
> If MODE9 bit is set into the Mode Register or if USMODE is set to
> either LIN_MASTER, LIN_SLAVE or LON_MODE, FIFOs operate in single
> data mode. Otherwise, they operate in multiple data mode.
> 
> In this new multiple data mode, accesses to the Receive Holding
> Register or Transmit Holding Register slightly change.
> 
> Since this driver implements neither the 9bit data feature (MODE9 bit
> set into the Mode Register) nor LIN modes, the USART works in
> multiple data mode whenever FIFOs are available and enabled. We also
> assume that data are 8bit wide.
> 
> In single data mode, 32bit access CAN be used to read a single data
> from RHR or write a single data into THR.
> However in multiple data mode, a 32bit access to RHR now allows us to
> read four consecutive data from RX FIFO. Also a 32bit access to THR
> now allows to write four consecutive data into TX FIFO. So we MUST
> use 8bit access whenever only one data have to be read/written at a
> time.
> 
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@...el.com>

Acked-by: Nicolas Ferre <nicolas.ferre@...el.com>
Thanks!

> ---
>  drivers/tty/serial/atmel_serial.c | 100 +++++++++++++++++++++++++++++++++++---
>  include/linux/atmel_serial.h      |  36 ++++++++++++++
>  2 files changed, 130 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index e7c337de31d1..87de21f0c7a3 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -56,6 +56,15 @@
>  /* Revisit: We should calculate this based on the actual port settings */
>  #define PDC_RX_TIMEOUT		(3 * 10)		/* 3 bytes */
>  
> +/* The minium number of data FIFOs should be able to contain */
> +#define ATMEL_MIN_FIFO_SIZE	8
> +/*
> + * These two offsets are substracted from the RX FIFO size to define the RTS
> + * high and low thresholds
> + */
> +#define ATMEL_RTS_HIGH_OFFSET	16
> +#define ATMEL_RTS_LOW_OFFSET	20
> +
>  #if defined(CONFIG_SERIAL_ATMEL_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
>  #define SUPPORT_SYSRQ
>  #endif
> @@ -141,6 +150,9 @@ struct atmel_uart_port {
>  	struct mctrl_gpios	*gpios;
>  	int			gpio_irq[UART_GPIO_MAX];
>  	unsigned int		tx_done_mask;
> +	u32			fifo_size;
> +	u32			rts_high;
> +	u32			rts_low;
>  	bool			ms_irq_enabled;
>  	bool			is_usart;	/* usart or uart */
>  	struct timer_list	uart_timer;	/* uart timer */
> @@ -191,6 +203,16 @@ static inline void atmel_uart_writel(struct uart_port *port, u32 reg, u32 value)
>  	__raw_writel(value, port->membase + reg);
>  }
>  
> +static inline u8 atmel_uart_readb(struct uart_port *port, u32 reg)
> +{
> +	return __raw_readb(port->membase + reg);
> +}
> +
> +static inline void atmel_uart_writeb(struct uart_port *port, u32 reg, u8 value)
> +{
> +	__raw_writeb(value, port->membase + reg);
> +}
> +
>  #ifdef CONFIG_SERIAL_ATMEL_PDC
>  static bool atmel_use_pdc_rx(struct uart_port *port)
>  {
> @@ -635,7 +657,7 @@ static void atmel_rx_chars(struct uart_port *port)
>  
>  	status = atmel_uart_readl(port, ATMEL_US_CSR);
>  	while (status & ATMEL_US_RXRDY) {
> -		ch = atmel_uart_readl(port, ATMEL_US_RHR);
> +		ch = atmel_uart_readb(port, ATMEL_US_RHR);
>  
>  		/*
>  		 * note that the error handling code is
> @@ -686,7 +708,7 @@ static void atmel_tx_chars(struct uart_port *port)
>  
>  	if (port->x_char &&
>  	    (atmel_uart_readl(port, ATMEL_US_CSR) & atmel_port->tx_done_mask)) {
> -		atmel_uart_writel(port, ATMEL_US_THR, port->x_char);
> +		atmel_uart_writeb(port, ATMEL_US_THR, port->x_char);
>  		port->icount.tx++;
>  		port->x_char = 0;
>  	}
> @@ -695,7 +717,7 @@ static void atmel_tx_chars(struct uart_port *port)
>  
>  	while (atmel_uart_readl(port, ATMEL_US_CSR) &
>  	       atmel_port->tx_done_mask) {
> -		atmel_uart_writel(port, ATMEL_US_THR, xmit->buf[xmit->tail]);
> +		atmel_uart_writeb(port, ATMEL_US_THR, xmit->buf[xmit->tail]);
>  		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
>  		port->icount.tx++;
>  		if (uart_circ_empty(xmit))
> @@ -1796,6 +1818,29 @@ static int atmel_startup(struct uart_port *port)
>  			atmel_set_ops(port);
>  	}
>  
> +	/*
> +	 * Enable FIFO when available
> +	 */
> +	if (atmel_port->fifo_size) {
> +		unsigned int txrdym = ATMEL_US_ONE_DATA;
> +		unsigned int rxrdym = ATMEL_US_ONE_DATA;
> +		unsigned int fmr;
> +
> +		atmel_uart_writel(port, ATMEL_US_CR,
> +				  ATMEL_US_FIFOEN |
> +				  ATMEL_US_RXFCLR |
> +				  ATMEL_US_TXFLCLR);
> +
> +		fmr = ATMEL_US_TXRDYM(txrdym) | ATMEL_US_RXRDYM(rxrdym);
> +		if (atmel_port->rts_high &&
> +		    atmel_port->rts_low)
> +			fmr |=	ATMEL_US_FRTSC |
> +				ATMEL_US_RXFTHRES(atmel_port->rts_high) |
> +				ATMEL_US_RXFTHRES2(atmel_port->rts_low);
> +
> +		atmel_uart_writel(port, ATMEL_US_FMR, fmr);
> +	}
> +
>  	/* Save current CSR for comparison in atmel_tasklet_func() */
>  	atmel_port->irq_status_prev = atmel_get_lines_status(port);
>  	atmel_port->irq_status = atmel_port->irq_status_prev;
> @@ -2213,7 +2258,7 @@ static int atmel_poll_get_char(struct uart_port *port)
>  	while (!(atmel_uart_readl(port, ATMEL_US_CSR) & ATMEL_US_RXRDY))
>  		cpu_relax();
>  
> -	return atmel_uart_readl(port, ATMEL_US_RHR);
> +	return atmel_uart_readb(port, ATMEL_US_RHR);
>  }
>  
>  static void atmel_poll_put_char(struct uart_port *port, unsigned char ch)
> @@ -2221,7 +2266,7 @@ static void atmel_poll_put_char(struct uart_port *port, unsigned char ch)
>  	while (!(atmel_uart_readl(port, ATMEL_US_CSR) & ATMEL_US_TXRDY))
>  		cpu_relax();
>  
> -	atmel_uart_writel(port, ATMEL_US_THR, ch);
> +	atmel_uart_writeb(port, ATMEL_US_THR, ch);
>  }
>  #endif
>  
> @@ -2328,7 +2373,7 @@ static void atmel_console_putchar(struct uart_port *port, int ch)
>  {
>  	while (!(atmel_uart_readl(port, ATMEL_US_CSR) & ATMEL_US_TXRDY))
>  		cpu_relax();
> -	atmel_uart_writel(port, ATMEL_US_THR, ch);
> +	atmel_uart_writeb(port, ATMEL_US_THR, ch);
>  }
>  
>  /*
> @@ -2603,6 +2648,48 @@ static int atmel_init_gpios(struct atmel_uart_port *p, struct device *dev)
>  	return 0;
>  }
>  
> +static void atmel_serial_probe_fifos(struct atmel_uart_port *port,
> +				     struct platform_device *pdev)
> +{
> +	port->fifo_size = 0;
> +	port->rts_low = 0;
> +	port->rts_high = 0;
> +
> +	if (of_property_read_u32(pdev->dev.of_node,
> +				 "atmel,fifo-size",
> +				 &port->fifo_size))
> +		return;
> +
> +	if (!port->fifo_size)
> +		return;
> +
> +	if (port->fifo_size < ATMEL_MIN_FIFO_SIZE) {
> +		port->fifo_size = 0;
> +		dev_err(&pdev->dev, "Invalid FIFO size\n");
> +		return;
> +	}
> +
> +	/*
> +	 * 0 <= rts_low <= rts_high <= fifo_size
> +	 * Once their CTS line asserted by the remote peer, some x86 UARTs tend
> +	 * to flush their internal TX FIFO, commonly up to 16 data, before
> +	 * actually stopping to send new data. So we try to set the RTS High
> +	 * Threshold to a reasonably high value respecting this 16 data
> +	 * empirical rule when possible.
> +	 */
> +	port->rts_high = max_t(int, port->fifo_size >> 1,
> +			       port->fifo_size - ATMEL_RTS_HIGH_OFFSET);
> +	port->rts_low  = max_t(int, port->fifo_size >> 2,
> +			       port->fifo_size - ATMEL_RTS_LOW_OFFSET);
> +
> +	dev_info(&pdev->dev, "Using FIFO (%u data)\n",
> +		 port->fifo_size);
> +	dev_dbg(&pdev->dev, "RTS High Threshold : %2u data\n",
> +		port->rts_high);
> +	dev_dbg(&pdev->dev, "RTS Low Threshold  : %2u data\n",
> +		port->rts_low);
> +}
> +
>  static int atmel_serial_probe(struct platform_device *pdev)
>  {
>  	struct atmel_uart_port *port;
> @@ -2639,6 +2726,7 @@ static int atmel_serial_probe(struct platform_device *pdev)
>  	port = &atmel_ports[ret];
>  	port->backup_imr = 0;
>  	port->uart.line = ret;
> +	atmel_serial_probe_fifos(port, pdev);
>  
>  	spin_lock_init(&port->lock_suspended);
>  
> diff --git a/include/linux/atmel_serial.h b/include/linux/atmel_serial.h
> index c384c21d65f0..ee696d7e8a43 100644
> --- a/include/linux/atmel_serial.h
> +++ b/include/linux/atmel_serial.h
> @@ -35,6 +35,11 @@
>  #define	ATMEL_US_DTRDIS		BIT(17)	/* Data Terminal Ready Disable */
>  #define	ATMEL_US_RTSEN		BIT(18)	/* Request To Send Enable */
>  #define	ATMEL_US_RTSDIS		BIT(19)	/* Request To Send Disable */
> +#define	ATMEL_US_TXFCLR		BIT(24)	/* Transmit FIFO Clear */
> +#define	ATMEL_US_RXFCLR		BIT(25)	/* Receive FIFO Clear */
> +#define	ATMEL_US_TXFLCLR	BIT(26)	/* Transmit FIFO Lock Clear */
> +#define	ATMEL_US_FIFOEN		BIT(30)	/* FIFO enable */
> +#define	ATMEL_US_FIFODIS	BIT(31)	/* FIFO disable */
>  
>  #define ATMEL_US_MR		0x04	/* Mode Register */
>  #define	ATMEL_US_USMODE		GENMASK(3, 0)	/* Mode of the USART */
> @@ -124,6 +129,37 @@
>  #define ATMEL_US_NER		0x44	/* Number of Errors Register */
>  #define ATMEL_US_IF		0x4c	/* IrDA Filter Register */
>  
> +#define ATMEL_US_CMPR		0x90	/* Comparaison Register */
> +#define ATMEL_US_FMR		0xa0	/* FIFO Mode Register */
> +#define	ATMEL_US_TXRDYM(data)	(((data) & 0x3) << 0)	/* TX Ready Mode */
> +#define	ATMEL_US_RXRDYM(data)	(((data) & 0x3) << 4)	/* RX Ready Mode */
> +#define		ATMEL_US_ONE_DATA	0x0
> +#define		ATMEL_US_TWO_DATA	0x1
> +#define		ATMEL_US_FOUR_DATA	0x2
> +#define	ATMEL_US_FRTSC		BIT(7)	/* FIFO RTS pin Control */
> +#define	ATMEL_US_TXFTHRES(thr)	(((thr) & 0x3f) << 8)	/* TX FIFO Threshold */
> +#define	ATMEL_US_RXFTHRES(thr)	(((thr) & 0x3f) << 16)	/* RX FIFO Threshold */
> +#define	ATMEL_US_RXFTHRES2(thr)	(((thr) & 0x3f) << 24)	/* RX FIFO Threshold2 */
> +
> +#define ATMEL_US_FLR		0xa4	/* FIFO Level Register */
> +#define	ATMEL_US_TXFL(reg)	(((reg) >> 0) & 0x3f)	/* TX FIFO Level */
> +#define	ATMEL_US_RXFL(reg)	(((reg) >> 16) & 0x3f)	/* RX FIFO Level */
> +
> +#define ATMEL_US_FIER		0xa8	/* FIFO Interrupt Enable Register */
> +#define ATMEL_US_FIDR		0xac	/* FIFO Interrupt Disable Register */
> +#define ATMEL_US_FIMR		0xb0	/* FIFO Interrupt Mask Register */
> +#define ATMEL_US_FESR		0xb4	/* FIFO Event Status Register */
> +#define	ATMEL_US_TXFEF		BIT(0)	/* Transmit FIFO Empty Flag */
> +#define	ATMEL_US_TXFFF		BIT(1)	/* Transmit FIFO Full Flag */
> +#define	ATMEL_US_TXFTHF		BIT(2)	/* Transmit FIFO Threshold Flag */
> +#define	ATMEL_US_RXFEF		BIT(3)	/* Receive FIFO Empty Flag */
> +#define	ATMEL_US_RXFFF		BIT(4)	/* Receive FIFO Full Flag */
> +#define	ATMEL_US_RXFTHF		BIT(5)	/* Receive FIFO Threshold Flag */
> +#define	ATMEL_US_TXFPTEF	BIT(6)	/* Transmit FIFO Pointer Error Flag */
> +#define	ATMEL_US_RXFPTEF	BIT(7)	/* Receive FIFO Pointer Error Flag */
> +#define	ATMEL_US_TXFLOCK	BIT(8)	/* Transmit FIFO Lock (FESR only) */
> +#define	ATMEL_US_RXFTHF2	BIT(9)	/* Receive FIFO Threshold Flag 2 */
> +
>  #define ATMEL_US_NAME		0xf0	/* Ip Name */
>  #define ATMEL_US_VERSION	0xfc	/* Ip Version */
>  
> 


-- 
Nicolas Ferre
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists