From 5816269e4ee3db2bc2ad44afc89f4abe81c7aa26 Mon Sep 17 00:00:00 2001 From: Paul Walmsley Date: Wed, 25 Jan 2012 19:50:36 -0700 Subject: [PATCH] tty: serial: OMAP: use a 1-byte RX FIFO threshold in PIO mode In the (default) PIO mode, use a one-byte RX FIFO threshold. The OMAP UART IP blocks do not appear to be capable of waking the system under an RX timeout condition. Since the previous RX FIFO threshold was 16 bytes, this meant that omap-serial.c did not become aware of any received data until all those bytes arrived or until another UART interrupt occurred. This made the serial console and presumably other serial applications (GPS, serial Bluetooth) unusable or extremely slow. A 1-byte RX FIFO threshold also allows the MPU to enter a low-power consumption state while waiting for the FIFO to fill. This can be verified using the serial console by comparing the behavior when "0123456789abcde" is pasted in from another window, with the behavior when "0123456789abcdef" is pasted in. Since the former string is less than sixteen bytes long, the string is not echoed for some time, while the latter string is echoed immediately. DMA operation is unaffected by this patch. Thanks to Russell King - ARM Linux for some additional information on the standard behavior of the RX timeout event, which was used to improve this commit description. Signed-off-by: Paul Walmsley Cc: Tomi Valkeinen Cc: Govindraj Raja Cc: Alan Cox Cc: Russell King Reviewed-by: Kevin Hilman Tested-by: Kevin Hilman Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/omap-serial.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c index d192dcb..c9c9ba2 100644 --- a/drivers/tty/serial/omap-serial.c +++ b/drivers/tty/serial/omap-serial.c @@ -46,6 +46,13 @@ #define DEFAULT_CLK_SPEED 48000000 /* 48Mhz*/ +/* SCR register bitmasks */ +#define OMAP_UART_SCR_RX_TRIG_GRANU1_MASK (1 << 7) + +/* FCR register bitmasks */ +#define OMAP_UART_FCR_RX_FIFO_TRIG_SHIFT 6 +#define OMAP_UART_FCR_RX_FIFO_TRIG_MASK (0x3 << 6) + static struct uart_omap_port *ui[OMAP_MAX_HSUART_PORTS]; /* Forward declaration of functions */ @@ -811,14 +818,21 @@ serial_omap_set_termios(struct uart_port *port, struct ktermios *termios, up->mcr = serial_in(up, UART_MCR); serial_out(up, UART_MCR, up->mcr | UART_MCR_TCRTLR); /* FIFO ENABLE, DMA MODE */ - serial_out(up, UART_FCR, up->fcr); - serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B); + + up->scr |= OMAP_UART_SCR_RX_TRIG_GRANU1_MASK; if (up->use_dma) { serial_out(up, UART_TI752_TLR, 0); - up->scr |= (UART_FCR_TRIGGER_4 | UART_FCR_TRIGGER_8); + up->scr |= UART_FCR_TRIGGER_4; + } else { + /* Set receive FIFO threshold to 1 byte */ + up->fcr &= ~OMAP_UART_FCR_RX_FIFO_TRIG_MASK; + up->fcr |= (0x1 << OMAP_UART_FCR_RX_FIFO_TRIG_SHIFT); } + serial_out(up, UART_FCR, up->fcr); + serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B); + serial_out(up, UART_OMAP_SCR, up->scr); serial_out(up, UART_EFR, up->efr); -- 2.7.4