From 5f6d851564a978085e23ccc41ee95cfa3a2ee43e Mon Sep 17 00:00:00 2001 From: Nobuhiro Iwamatsu Date: Tue, 17 Mar 2015 01:19:54 +0900 Subject: [PATCH] serial: sh-sci: Update calculation of timeout for DMA The current calculation method in the case of 9600bps, rounding error occurs has become setting that occur timeout faster than the required time. When we use 9600bps, 32byte buffer, 10 bit (CS8) and 100 HZ, it becomes 3 jiffies (30msec). In fact it is necessary 33msec. This updates to the calculation that are not actually less than the value set by the rounding error. Also, this is nothing will be calculated value when there is no load. If there are a lot of case load, overrun error will occur immediately. This is by the buffer size to be calculated twice the DMA buffer, and add the change of setting a sufficient time-out value. Signed-off-by: Nobuhiro Iwamatsu Signed-off-by: Yoshihiro Kaneko Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/sh-sci.c | 40 ++++++++++++++++++++++++++++--------- 1 file changed, 31 insertions(+), 9 deletions(-) diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index 5bf997253a46..e7d6566fafaf 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -1991,18 +1991,40 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios, #ifdef CONFIG_SERIAL_SH_SCI_DMA /* - * Calculate delay for 1.5 DMA buffers: see - * drivers/serial/serial_core.c::uart_update_timeout(). With 10 bits - * (CS8), 250Hz, 115200 baud and 64 bytes FIFO, the above function + * Calculate delay for 2 DMA buffers (4 FIFO). + * See drivers/serial/serial_core.c::uart_update_timeout(). With 10 + * bits (CS8), 250Hz, 115200 baud and 64 bytes FIFO, the above function * calculates 1 jiffie for the data plus 5 jiffies for the "slop(e)." - * Then below we calculate 3 jiffies (12ms) for 1.5 DMA buffers (3 FIFO - * sizes), but it has been found out experimentally, that this is not - * enough: the driver too often needlessly runs on a DMA timeout. 20ms - * as a minimum seem to work perfectly. + * Then below we calculate 5 jiffies (20ms) for 2 DMA buffers (4 FIFO + * sizes), but when performing a faster transfer, value obtained by + * this formula is may not enough. Therefore, if value is smaller than + * 20msec, this sets 20msec as timeout of DMA. */ if (s->chan_rx) { - s->rx_timeout = (port->timeout - HZ / 50) * s->buf_len_rx * 3 / - port->fifosize / 2; + unsigned int bits; + + /* byte size and parity */ + switch (termios->c_cflag & CSIZE) { + case CS5: + bits = 7; + break; + case CS6: + bits = 8; + break; + case CS7: + bits = 9; + break; + default: + bits = 10; + break; + } + + if (termios->c_cflag & CSTOPB) + bits++; + if (termios->c_cflag & PARENB) + bits++; + s->rx_timeout = DIV_ROUND_UP((s->buf_len_rx * 2 * bits * HZ) / + (baud / 10), 10); dev_dbg(port->dev, "DMA Rx t-out %ums, tty t-out %u jiffies\n", s->rx_timeout * 1000 / HZ, port->timeout); if (s->rx_timeout < msecs_to_jiffies(20)) -- 2.39.5