Subject: [PATCH linux-next v2 3/4] tty/serial: at91: add support to FIFOs

From: [email-masked] (Nicolas Ferre)
Date: Mon, 29 Jun 2015 15:11:18 +0200

Le 11/06/2015 18:20, Cyrille Pitchen a ?crit :
> 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 <[email-masked]>
> ---
>  drivers/tty/serial/atmel_serial.c | 79 ++++++++++++++++++++++++++++++++++++++-
>  include/linux/atmel_serial.h      | 36 ++++++++++++++++++
>  2 files changed, 113 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index 112e74b..6767570 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -96,8 +96,8 @@ static void atmel_stop_rx(struct uart_port *port);
>  #define UART_PUT_IDR(port, v)  __raw_writel(v, (port)->membase + ATMEL_US_IDR)
>  #define UART_GET_IMR(port)     __raw_readl((port)->membase + ATMEL_US_IMR)
>  #define UART_GET_CSR(port)     __raw_readl((port)->membase + ATMEL_US_CSR)
> -#define UART_GET_CHAR(port)    __raw_readl((port)->membase + ATMEL_US_RHR)
> -#define UART_PUT_CHAR(port, v) __raw_writel(v, (port)->membase + ATMEL_US_THR)
> +#define UART_GET_CHAR(port)    __raw_readb((port)->membase + ATMEL_US_RHR)
> +#define UART_PUT_CHAR(port, v) __raw_writeb(v, (port)->membase + ATMEL_US_THR)
>  #define UART_GET_BRGR(port)    __raw_readl((port)->membase + ATMEL_US_BRGR)
>  #define UART_PUT_BRGR(port, v) __raw_writel(v, (port)->membase + ATMEL_US_BRGR)
>  #define UART_PUT_RTOR(port, v) __raw_writel(v, (port)->membase + ATMEL_US_RTOR)
> @@ -119,6 +119,16 @@ static void atmel_stop_rx(struct uart_port *port);
>  #define UART_PUT_TCR(port, v)  __raw_writel(v, (port)->membase + ATMEL_PDC_TCR)
>  #define UART_GET_TCR(port)     __raw_readl((port)->membase + ATMEL_PDC_TCR)
>  
> +/* FIFO registers */
> +#define UART_PUT_FMR(port, v)  __raw_writel(v, (port)->membase + ATMEL_US_FMR)
> +#define UART_GET_FMR(port)     __raw_readl((port)->membase + ATMEL_US_FMR)
> +#define UART_GET_FESR(port)    __raw_readl((port)->membase + ATMEL_US_FESR)
> +#define UART_PUT_FIER(port, v) __raw_writel(v, (port)->membase + ATMEL_US_FIER)
> +#define UART_PUT_FIDR(port, v) __raw_writel(v, (port)->membase + ATMEL_US_FIDR)
> +#define UART_GET_FIMR(port)    __raw_readl((port)->membase + ATMEL_US_FIMR)
> +#define UART_GET_FLR(port)     __raw_readl((port)->membase + ATMEL_US_FLR)
> +
> +
>  struct atmel_dma_buffer {
>  	unsigned char	*buf;
>  	dma_addr_t	dma_addr;
> @@ -172,6 +182,9 @@ 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 */
> @@ -1797,6 +1810,29 @@ 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;
> +
> +		UART_PUT_CR(port,
> +			    ATMEL_US_FIFOEN |
> +			    ATMEL_US_RXFCLR |
> +			    ATMEL_US_TXFLCLR);
> +
> +		fmr = ATMEL_US_TXRDYM(txrdym) | ATMEL_US_RXRDYM(rxrdym);

If above is the only place where we use txrdym and rxrdym, why not use
directly the defined constants here?

> +		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);
> +
> +		UART_PUT_FMR(port, 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;
> @@ -2599,6 +2635,44 @@ 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) ||
> +	    !port->fifo_size)

I understand, but here, please split the test in 2: it's far more readable.

> +		return;
> +
> +	if (port->fifo_size < 8 || port->fifo_size > 32) {

Can you define constants for these 2 values and use them here?

> +		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 8 data, before
> +	 * actually stopping to send new data. So we try to set the RTS High
> +	 * Threshold to a raisonable high value respecting this 8 data empirical
> +	 * rule when possible.
> +	 */
> +	port->rts_high = max_t(int, port->fifo_size >> 1, port->fifo_size - 8);
> +	port->rts_low  = max_t(int, port->fifo_size >> 2, port->fifo_size - 16);

Same here: I'd prefer constants with meaningful names.

> +
> +	dev_info(&pdev->dev, "Using FIFO (%u data)\n",
> +		 port->fifo_size);

Okay for this information.

> +	dev_info(&pdev->dev, "RTS High Threshold : %2u data\n",
> +		 port->rts_high);
> +	dev_info(&pdev->dev, "RTS Low Threshold  : %2u data\n",
> +		 port->rts_low);

Aren't these two other dev_info() better suited as dev_dbg()?

> +}
> +
>  static int atmel_serial_probe(struct platform_device *pdev)
>  {
>  	struct atmel_uart_port *port;
> @@ -2635,6 +2709,7 @@ 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 c384c21..ee696d7 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 */

Otherwise it look good.

Thanks, bye,
-- 
Nicolas Ferre