[PATCH] serial: sh-sci: remove obsolete latency workaround

[PATCH] serial: sh-sci: remove obsolete latency workaround

[Ulrich Hecht]

Since the transition to hrtimers there is no more need to set a minimum
RX timeout to work around latency issues.

Signed-off-by: Ulrich Hecht <uli+renesas@fpond.eu>
---
 drivers/tty/serial/sh-sci.c | 13 +------------
 1 file changed, 1 insertion(+), 12 deletions(-)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index e3af97a59856..ef37fdf37612 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -2609,21 +2609,10 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios,
 		udelay(DIV_ROUND_UP(10 * 1000000, baud));
 	}
 
-	/*
-	 * Calculate delay for 2 DMA buffers (4 FIFO).
-	 * See 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 5 jiffies (20ms) for 2 DMA
-	 * buffers (4 FIFO sizes), but when performing a faster transfer, the
-	 * value obtained by this formula is too small. Therefore, if the value
-	 * is smaller than 20ms, use 20ms as the timeout value for DMA.
-	 */
+	/* Calculate delay for 2 DMA buffers (4 FIFO). */
 	s->rx_frame = (10000 * bits) / (baud / 100);
 #ifdef CONFIG_SERIAL_SH_SCI_DMA
 	s->rx_timeout = s->buf_len_rx * 2 * s->rx_frame;
-	if (s->rx_timeout < 20)
-		s->rx_timeout = 20;
 #endif
 
 	if ((termios->c_cflag & CREAD) != 0)
-- 
2.20.1

Re: [PATCH] serial: sh-sci: remove obsolete latency workaround

[Greg KH]

On Tue, Apr 13, 2021 at 10:46:11AM +0200, Ulrich Hecht wrote:
> Since the transition to hrtimers there is no more need to set a minimum
> RX timeout to work around latency issues.
> 
> Signed-off-by: Ulrich Hecht <uli+renesas@fpond.eu>
> ---
>  drivers/tty/serial/sh-sci.c | 13 +------------
>  1 file changed, 1 insertion(+), 12 deletions(-)

$ ./scripts/get_maintainer.pl --file drivers/tty/serial/sh-sci.c
Greg Kroah-Hartman <gregkh@linuxfoundation.org> (maintainer:SERIAL DRIVERS)
Jiri Slaby <jirislaby@kernel.org> (supporter:TTY LAYER)
linux-serial@vger.kernel.org (open list:SERIAL DRIVERS)
linux-kernel@vger.kernel.org (open list)

{sigh}

Care to resend this and cc: the other developers here?

thanks,

greg k-h

Re: [PATCH] serial: sh-sci: remove obsolete latency workaround

[Ulrich Hecht]

> On 04/15/2021 10:12 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> Care to resend this and cc: the other developers here?

Done. Sorry for the inconvenience.

CU
Uli

[PATCH] serial: sh-sci: remove obsolete latency workaround

[Ulrich Hecht]

Since the transition to hrtimers there is no more need to set a minimum
RX timeout to work around latency issues.

Signed-off-by: Ulrich Hecht <uli+renesas@fpond.eu>
---
 drivers/tty/serial/sh-sci.c | 13 +------------
 1 file changed, 1 insertion(+), 12 deletions(-)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index e3af97a59856..ef37fdf37612 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -2609,21 +2609,10 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios,
 		udelay(DIV_ROUND_UP(10 * 1000000, baud));
 	}
 
-	/*
-	 * Calculate delay for 2 DMA buffers (4 FIFO).
-	 * See 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 5 jiffies (20ms) for 2 DMA
-	 * buffers (4 FIFO sizes), but when performing a faster transfer, the
-	 * value obtained by this formula is too small. Therefore, if the value
-	 * is smaller than 20ms, use 20ms as the timeout value for DMA.
-	 */
+	/* Calculate delay for 2 DMA buffers (4 FIFO). */
 	s->rx_frame = (10000 * bits) / (baud / 100);
 #ifdef CONFIG_SERIAL_SH_SCI_DMA
 	s->rx_timeout = s->buf_len_rx * 2 * s->rx_frame;
-	if (s->rx_timeout < 20)
-		s->rx_timeout = 20;
 #endif
 
 	if ((termios->c_cflag & CREAD) != 0)
-- 
2.20.1

RE: [PATCH] serial: sh-sci: remove obsolete latency workaround

[Yoshihiro Shimoda]

Hi Ulrich-san,

> From: Ulrich Hecht, Sent: Thursday, April 15, 2021 6:36 PM
> 
> Since the transition to hrtimers there is no more need to set a minimum
> RX timeout to work around latency issues.
> 
> Signed-off-by: Ulrich Hecht <uli+renesas@fpond.eu>

Thank you for the patch!

Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>

Best regards,
Yoshihiro Shimoda