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From: bigeasy@linutronix.de (Sebastian Andrzej Siewior)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 10/16] tty: serial: 8250_dma: optimize the xmit path due to UART_BUG_DMA_TX
Date: Wed, 10 Sep 2014 21:30:05 +0200
Message-ID: <1410377411-26656-11-git-send-email-bigeasy@linutronix.de> (raw)
In-Reply-To: <1410377411-26656-1-git-send-email-bigeasy@linutronix.de>

Due to UART_BUG_DMA_TX the am335x has to put the first one byte into the
TX FIFO to get things going. If we get to serial8250_tx_dma() via
__dma_tx_complete() then the DMA engine just finished and the FIFO is
full and we can't put the first byte into the TX FIFO as kick start so
we leave with THRI enabled.
The result is that we end up manually filling the FIFO. We could be a
little better at this and try DMA once again. If it works, it works and
if not we do it manually.

v8?v9:
	- fix receiving THRI interrupts after DMA operation completed and
	  the next one would fail (length < 4 bytes).
	- while at it makes sure we fail with an error for zero lenght
	  transfers with the TX bug or runtime PM
	- make sure THRI is always cleared after DMA is fired.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/tty/serial/8250/8250_core.c | 17 +++++++++++++++--
 drivers/tty/serial/8250/8250_dma.c  | 27 +++++++++++++++++++--------
 2 files changed, 34 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 39b1c7318f17..660d19771bbe 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -1599,9 +1599,22 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
 	serial8250_modem_status(up);
 	if ((!up->dma || (up->dma && up->dma->tx_err)) &&
 			(status & UART_LSR_THRE)) {
-		serial8250_tx_chars(up);
-	}
+		if (!up->dma) {
+			serial8250_tx_chars(up);
+		} else {
+			if (uart_tx_stopped(&up->port) ||
+				uart_circ_empty(&up->port.state->xmit)) {
+				up->dma->tx_err = 0;
+				serial8250_tx_chars(up);
 
+			} else  {
+				/* try again due to UART_BUG_DMA_TX+full fifo */
+				dma_err = serial8250_tx_dma(up);
+				if (dma_err)
+					serial8250_tx_chars(up);
+			}
+		}
+	}
 	spin_unlock_irqrestore(&port->lock, flags);
 	return 1;
 }
diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
index 48dc57aad0dd..e836d128e63a 100644
--- a/drivers/tty/serial/8250/8250_dma.c
+++ b/drivers/tty/serial/8250/8250_dma.c
@@ -86,12 +86,23 @@ int serial8250_tx_dma(struct uart_8250_port *p)
 	unsigned int			skip_byte = 0;
 	int ret;
 
-	if (uart_tx_stopped(&p->port) || dma->tx_running ||
-	    uart_circ_empty(xmit))
+	if (dma->tx_running)
 		return 0;
+	if (uart_tx_stopped(&p->port) || uart_circ_empty(xmit)) {
 
-	dma->tx_size = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
+		/*
+		 * Even if no data, we need to return an error for the two cases
+		 * below so serial8250_tx_chars() is invoked and properly clears
+		 * THRI and/or runtime suspend.
+		 */
+		if (dma->tx_err || p->capabilities & UART_CAP_RPM) {
+			ret = -EBUSY;
+			goto err;
+		}
+		return 0;
+	}
 
+	dma->tx_size = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
 	if (p->bugs & UART_BUG_DMA_TX) {
 		u8 tx_lvl;
 
@@ -142,12 +153,12 @@ int serial8250_tx_dma(struct uart_8250_port *p)
 				   UART_XMIT_SIZE, DMA_TO_DEVICE);
 
 	dma_async_issue_pending(dma->txchan);
-	if (dma->tx_err) {
+	if (dma->tx_err)
 		dma->tx_err = 0;
-		if (p->ier & UART_IER_THRI) {
-			p->ier &= ~UART_IER_THRI;
-			serial_out(p, UART_IER, p->ier);
-		}
+
+	if (p->ier & UART_IER_THRI) {
+		p->ier &= ~UART_IER_THRI;
+		serial_out(p, UART_IER, p->ier);
 	}
 	if (skip_byte)
 		serial_out(p, UART_TX, xmit->buf[xmit->tail]);
-- 
2.1.0

  parent reply index

Thread overview: 97+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-10 19:29 [PATCH 00/16 v9] omap 8250 based uart + DMA Sebastian Andrzej Siewior
2014-09-10 19:29 ` [PATCH 01/16] tty: serial: 8250_core: allow to set ->throttle / ->unthrottle callbacks Sebastian Andrzej Siewior
2014-09-10 19:29 ` [PATCH 02/16] tty: serial: 8250_core: add run time pm Sebastian Andrzej Siewior
2014-09-29  9:46   ` Frans Klaver
2014-09-29 13:39     ` Sebastian Andrzej Siewior
2014-09-10 19:29 ` [PATCH 03/16] tty: serial: 8250_core: read only RX if there is something in the FIFO Sebastian Andrzej Siewior
2015-02-09 13:34   ` Nicolas Schichan
2015-02-09 23:34     ` Peter Hurley
2015-02-10  9:32       ` Sebastian Andrzej Siewior
2015-02-10 12:04       ` Nicolas Schichan
2015-02-10 17:46         ` Peter Hurley
2015-02-11 20:01           ` Peter Hurley
2015-02-11 20:03             ` Tony Lindgren
2015-02-11 20:42               ` Peter Hurley
2015-02-12  8:45                 ` Sebastian Andrzej Siewior
2015-02-12  9:40                   ` Russell King - ARM Linux
2015-02-12 16:32                   ` Peter Hurley
2015-02-12 19:23                     ` Sebastian Andrzej Siewior
2015-02-12 19:55                       ` Peter Hurley
2015-02-12 20:34                         ` Sebastian Andrzej Siewior
2015-02-13 18:51                         ` Sebastian Andrzej Siewior
2015-02-13 23:15                           ` Russell King - ARM Linux
2015-02-15 17:32                             ` [PATCH] serial: 8250: Revert "tty: serial: 8250_core: read only RX if there is something in the FIFO" Sebastian Andrzej Siewior
2015-05-12 20:25                               ` Tony Lindgren
2014-09-10 19:29 ` [PATCH 04/16] tty: serial: 8250_core: use the ->line argument as a hint in serial8250_find_match_or_unused() Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 05/16] tty: serial: 8250_core: remove UART_IER_RDI in serial8250_stop_rx() Sebastian Andrzej Siewior
2014-09-11 11:19   ` Heikki Krogerus
2014-09-10 19:30 ` [PATCH 06/16] tty: serial: Add 8250-core based omap driver Sebastian Andrzej Siewior
2014-09-11 11:57   ` Peter Hurley
2014-09-16 17:01     ` Sebastian Andrzej Siewior
2014-09-29  9:38   ` Frans Klaver
2014-09-29 13:27     ` Sebastian Andrzej Siewior
2014-09-29 13:34       ` Frans Klaver
2014-09-10 19:30 ` [PATCH 07/16] tty: serial: 8250_dma: handle error on TX submit Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 08/16] tty: serial: 8250_dma: enqueue RX dma again on completion Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx Sebastian Andrzej Siewior
2014-09-11 11:17   ` Heikki Krogerus
2014-09-11 11:42     ` Sebastian Andrzej Siewior
2014-09-11 12:32       ` Peter Hurley
2014-09-11 12:50         ` Sebastian Andrzej Siewior
2014-09-11 14:35           ` Peter Hurley
2014-09-15 17:01             ` Sebastian Andrzej Siewior
2014-09-16 16:55               ` Sebastian Andrzej Siewior
2014-09-17 12:20                 ` Peter Hurley
2014-09-17 16:25                   ` Sebastian Andrzej Siewior
2014-09-29 16:15                   ` Sebastian Andrzej Siewior
2014-09-11 15:11           ` Frans Klaver
2014-09-11 16:04             ` Sebastian Andrzej Siewior
2014-09-11 17:04               ` Frans Klaver
2014-09-12  7:23                 ` Sebastian Andrzej Siewior
     [not found]                   ` <20140912094010.GE28458@ci00147.xsens-tech.local>
2014-09-12  9:51                     ` Sebastian Andrzej Siewior
2014-09-12 10:28                       ` Frans Klaver
2014-09-15 16:42                         ` Sebastian Andrzej Siewior
2014-09-16  9:05                           ` Frans Klaver
2014-09-16 12:42                             ` Frans Klaver
2014-09-16 14:23                               ` Frans Klaver
2014-09-17 10:28                           ` Frans Klaver
2014-09-21 20:41                             ` Sebastian Andrzej Siewior
2014-09-22  9:28                               ` Frans Klaver
2014-09-24  7:56                                 ` Sebastian Andrzej Siewior
2014-09-25 15:14                                 ` Sebastian Andrzej Siewior
2014-09-25 15:18                                   ` Frans Klaver
2014-09-29  8:50                                   ` Frans Klaver
2014-09-29  9:54                                     ` Sebastian Andrzej Siewior
2014-09-29 10:30                                       ` Frans Klaver
2014-09-30  8:44                                         ` Frans Klaver
2014-10-02 10:27                                           ` Sebastian Andrzej Siewior
2014-10-13 14:55                                             ` Frans Klaver
2014-09-23 17:03                               ` Peter Hurley
2014-09-24  7:53                                 ` Sebastian Andrzej Siewior
2014-09-25 10:42                                   ` Sebastian Andrzej Siewior
2014-09-25 11:31                                     ` Peter Hurley
2014-09-25 13:11                                       ` Sebastian Andrzej Siewior
2014-09-17 16:34       ` Sebastian Andrzej Siewior
2014-09-19 10:22         ` Heikki Krogerus
2014-09-19 10:58           ` Sebastian Andrzej Siewior
2014-09-19 11:25             ` Peter Hurley
2014-09-22  7:46             ` Heikki Krogerus
2014-09-25  9:24               ` Sebastian Andrzej Siewior
2014-09-10 19:30 ` Sebastian Andrzej Siewior [this message]
2014-09-10 19:30 ` [PATCH 11/16] tty: serial: 8250_dma: keep own book keeping about RX transfers Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 12/16] tty: serial: 8250_dma: handle the UART RDI event while DMA remains idle Sebastian Andrzej Siewior
2014-09-29  9:23   ` Frans Klaver
2014-09-10 19:30 ` [PATCH 13/16] tty: serial: 8250_dma: add pm runtime Sebastian Andrzej Siewior
2014-09-29  9:26   ` Frans Klaver
2014-09-29  9:56     ` Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 14/16] arm: dts: am33xx: add DMA properties for UART Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 15/16] arm: dts: dra7: " Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 16/16] tty: serial: 8250: omap: add dma support Sebastian Andrzej Siewior
2014-09-12 22:43 ` [PATCH 00/16 v9] omap 8250 based uart + DMA Tony Lindgren
2014-09-15 11:50   ` Sebastian Andrzej Siewior
2014-09-16 12:57     ` Sebastian Andrzej Siewior
2014-09-16 16:48       ` Tony Lindgren
2014-09-16 21:30         ` Tony Lindgren
2014-09-17  8:38           ` Sebastian Andrzej Siewior
2014-09-17  9:05 ` Sebastian Andrzej Siewior
2014-09-26 16:02   ` Greg KH

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