Re: [PATCH linux-next v2 3/4] tty/serial: at91: add support to FIFOs
From: Nicolas Ferre
Date: Mon Jun 29 2015 - 09:12:38 EST
Le 11/06/2015 18:20, 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@xxxxxxxxx>
> ---
> 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
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