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

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Date:   Thu, 15 Apr 2021 11:35:47 +0200
From:   Ulrich Hecht <uli+renesas@...nd.eu>
To:     linux-renesas-soc@...r.kernel.org, linux-serial@...r.kernel.org
Cc:     wsa@...nel.org, geert@...ux-m68k.org,
        yoshihiro.shimoda.uh@...esas.com, gregkh@...uxfoundation.org,
        jirislaby@...nel.org, linux-kernel@...r.kernel.org,
        Ulrich Hecht <uli+renesas@...nd.eu>
Subject: [PATCH] serial: sh-sci: remove obsolete latency workaround

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@...nd.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