[PATCH v3 0/*] serial/amba-pl011: Activate TX IRQ passively

[PATCH v3 0/*] serial/amba-pl011: Activate TX IRQ passively

[Dave Martin]

Thanks to Jakub Kici?ski for his bug report and discussion, and for
showing out how we can manage without the softirq (and providing a
patch, though merging my rework with it got difficult, so I don't
include it in the series now).


There are two alternate versions of the series threaded from this cover
letter:

 * [PATCH v3] - patch against v4.0-rc5 that supersedes the previous
        series; this is the less churny option.

 * [PATCH v3, tty-next..] - patches against tty-next that
        modify/partially revert the previous series without needing a
        rebase.

Take your pick.


Changes since v2:

 * Remove the optimisation that assumes TXIS stays asserted across port
   shutdown..startup (thanks to Jakub Kici?ski for spotting this on
   raspberrypi-2).  This turns out to be untrue in certain situations,
   namely when the only process with the port open is killed by a
   signal.  This may indicate a bug in serial_core, but the "correct"
   behaviour for this case is not completely obvious.

   For this repost, I just revert the optimisation so that the pl011
   driver doesn't hang in this situation.  It didn't bring much real
   benefit in any case.

 * Remove the tx softirq and rework the code for more intelligible
   code flow.

 * pl011_start_tx() now simply stuffs the FIFO until it's full (in which
   case the TX IRQ will definitely fire), or until the serial_core
   circular buffer is empty (in which case we don't care about the
   interrupt because there is nothing more to send).


Original cover letter:

The current PL011 driver transmits a dummy character when the UART
is opened, to assert the TX IRQ for the first time
(see pl011_startup()).  The UART is put in loopback mode temporarily,
so the receiver presumably shouldn't see anything.

However...

At least some platforms containing a PL011 send characters down the
wire even when loopback mode is enabled.  This means that a
spurious NUL character may be seen at the receiver when the PL011 is
opened through the TTY layer.

The current code also temporarily sets the baud rate to maximum and
the character width to the minimum, to that the dummy TX completes
as quickly as possible.  If this is seen by the receiver it will
result in a framing error and can knock the receiver out of sync --
turning subsequent output into garbage until synchronisation
is reestablished.  (Particularly problematic during boot with systemd.)

To avoid spurious transmissions, this patch removes assumptions about
whether the TX IRQ will fire until at least one TX IRQ has been seen.

Instead, the UART will unmask the TX IRQ and then slow-start via
polling and timer-based soft IRQs initially.  If the TTY layer writes
enough data to fill the FIFO to the interrupt threshold in one go,
the TX IRQ should assert, at which point the driver changes to
fully interrupt-driven TX.

In this way, the TX IRQ is activated as a side-effect instead of
being done deliberately.

This should also mean that the driver works on the SBSA Generic
UART[1] (a cut-down PL011) without invasive changes.  The Generic
UART lacks some features needed for the dummy TX approach to work
(FIFO disabling and loopback).

[1] Server Base System Architecture (ARM-DEN-0029-v2.3)
    http://infocenter.arm.com/
    (click-thru required :/)

-- 
1.7.10.4

[PATCH v3 0/1] serial/amba-pl011: Activate TX IRQ passively

[Dave Martin]

(Rework based on v4.0-rc5)

The current PL011 driver transmits a dummy character when the UART
is opened, to assert the TX IRQ for the first time
(see pl011_startup()).  The UART is put in loopback mode temporarily,
so the receiver presumably shouldn't see anything.

However...

At least some platforms containing a PL011 send characters down the
wire even when loopback mode is enabled.  This means that a
spurious NUL character may be seen at the receiver when the PL011 is
opened through the TTY layer.

The current code also temporarily sets the baud rate to maximum and
the character width to the minimum, to that the dummy TX completes
as quickly as possible.  If this is seen by the receiver it will
result in a framing error and can knock the receiver out of sync --
turning subsequent output into garbage until synchronisation
is reestablished.  (Particularly problematic during boot with systemd.)

To avoid spurious transmissions, this patch removes assumptions about
whether the TX IRQ will fire until the FIFO has been filled.

This should also mean that the driver works on the SBSA Generic
UART[1] (a cut-down PL011) without invasive changes.  The Generic
UART lacks some features needed for the dummy TX approach to work
(FIFO disabling and loopback).

[1] Server Base System Architecture (ARM-DEN-0029-v2.3)
    http://infocenter.arm.com/
    (click-thru required :/)

Dave Martin (1):
  serial/amba-pl011: Activate TX IRQ passively

 drivers/tty/serial/amba-pl011.c |   88 +++++++++++++++++++--------------------
 1 file changed, 44 insertions(+), 44 deletions(-)

-- 
1.7.10.4

[PATCH v3] serial/amba-pl011: Activate TX IRQ passively

[Dave Martin]

The current PL011 driver transmits a dummy character when the UART
is opened, to assert the TX IRQ for the first time
(see pl011_startup()).  The UART is put in loopback mode temporarily,
so the receiver presumably shouldn't see anything.

However...

At least some platforms containing a PL011 send characters down the
wire even when loopback mode is enabled.  This means that a
spurious NUL character may be seen at the receiver when the PL011 is
opened through the TTY layer.

The current code also temporarily sets the baud rate to maximum and
the character width to the minimum, to that the dummy TX completes
as quickly as possible.  If this is seen by the receiver it will
result in a framing error and can knock the receiver out of sync --
turning subsequent output into garbage until synchronisation
is reestablished.  (Particularly problematic during boot with systemd.)

To avoid spurious transmissions, this patch removes assumptions about
whether the TX IRQ will fire until the FIFO has been filled.

This should also mean that the driver works on the SBSA Generic
UART[1] (a cut-down PL011) without invasive changes.  The Generic
UART lacks some features needed for the dummy TX approach to work
(FIFO disabling and loopback).

[1] Server Base System Architecture (ARM-DEN-0029-v2.3)
    http://infocenter.arm.com/
    (click-thru required :/)

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
---
 drivers/tty/serial/amba-pl011.c |   88 +++++++++++++++++++--------------------
 1 file changed, 44 insertions(+), 44 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 8d94c19..180b1d2 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -440,8 +440,9 @@ static void pl011_dma_remove(struct uart_amba_port *uap)
 		dma_release_channel(uap->dmarx.chan);
 }
 
-/* Forward declare this for the refill routine */
+/* Forward declare these for the refill routine */
 static int pl011_dma_tx_refill(struct uart_amba_port *uap);
+static void pl011_start_tx_pio(struct uart_amba_port *uap);
 
 /*
  * The current DMA TX buffer has been sent.
@@ -479,14 +480,13 @@ static void pl011_dma_tx_callback(void *data)
 		return;
 	}
 
-	if (pl011_dma_tx_refill(uap) <= 0) {
+	if (pl011_dma_tx_refill(uap) <= 0)
 		/*
 		 * We didn't queue a DMA buffer for some reason, but we
 		 * have data pending to be sent.  Re-enable the TX IRQ.
 		 */
-		uap->im |= UART011_TXIM;
-		writew(uap->im, uap->port.membase + UART011_IMSC);
-	}
+		pl011_start_tx_pio(uap);
+
 	spin_unlock_irqrestore(&uap->port.lock, flags);
 }
 
@@ -1208,15 +1208,23 @@ static void pl011_stop_tx(struct uart_port *port)
 	pl011_dma_tx_stop(uap);
 }
 
+static void pl011_tx_chars(struct uart_amba_port *uap, bool from_irq);
+
+/* Start TX with programmed I/O only (no DMA) */
+static void pl011_start_tx_pio(struct uart_amba_port *uap)
+{
+	uap->im |= UART011_TXIM;
+	writew(uap->im, uap->port.membase + UART011_IMSC);
+	pl011_tx_chars(uap, false);
+}
+
 static void pl011_start_tx(struct uart_port *port)
 {
 	struct uart_amba_port *uap =
 	    container_of(port, struct uart_amba_port, port);
 
-	if (!pl011_dma_tx_start(uap)) {
-		uap->im |= UART011_TXIM;
-		writew(uap->im, uap->port.membase + UART011_IMSC);
-	}
+	if (!pl011_dma_tx_start(uap))
+		pl011_start_tx_pio(uap);
 }
 
 static void pl011_stop_rx(struct uart_port *port)
@@ -1274,16 +1282,29 @@ __acquires(&uap->port.lock)
 	spin_lock(&uap->port.lock);
 }
 
-static void pl011_tx_chars(struct uart_amba_port *uap)
+static bool pl011_tx_char(struct uart_amba_port *uap, unsigned char c,
+			  bool from_irq)
+{
+	if (unlikely(!from_irq) &&
+	    readw(uap->port.membase + UART01x_FR) & UART01x_FR_TXFF)
+		return false; /* unable to transmit character */
+
+	writew(c, uap->port.membase + UART01x_DR);
+	uap->port.icount.tx++;
+
+	return true;
+}
+
+static void pl011_tx_chars(struct uart_amba_port *uap, bool from_irq)
 {
 	struct circ_buf *xmit = &uap->port.state->xmit;
-	int count;
+	int count = uap->fifosize >> 1;
 
 	if (uap->port.x_char) {
-		writew(uap->port.x_char, uap->port.membase + UART01x_DR);
-		uap->port.icount.tx++;
+		if (!pl011_tx_char(uap, uap->port.x_char, from_irq))
+			return;
 		uap->port.x_char = 0;
-		return;
+		--count;
 	}
 	if (uart_circ_empty(xmit) || uart_tx_stopped(&uap->port)) {
 		pl011_stop_tx(&uap->port);
@@ -1294,14 +1315,15 @@ static void pl011_tx_chars(struct uart_amba_port *uap)
 	if (pl011_dma_tx_irq(uap))
 		return;
 
-	count = uap->fifosize >> 1;
 	do {
-		writew(xmit->buf[xmit->tail], uap->port.membase + UART01x_DR);
-		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-		uap->port.icount.tx++;
-		if (uart_circ_empty(xmit))
+		if (likely(from_irq) && count-- == 0)
+			break;
+
+		if (!pl011_tx_char(uap, xmit->buf[xmit->tail], from_irq))
 			break;
-	} while (--count > 0);
+
+		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
+	} while (!uart_circ_empty(xmit));
 
 	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
 		uart_write_wakeup(&uap->port);
@@ -1373,7 +1395,7 @@ static irqreturn_t pl011_int(int irq, void *dev_id)
 				      UART011_CTSMIS|UART011_RIMIS))
 				pl011_modem_status(uap);
 			if (status & UART011_TXIS)
-				pl011_tx_chars(uap);
+				pl011_tx_chars(uap, true);
 
 			if (pass_counter-- == 0)
 				break;
@@ -1577,7 +1599,7 @@ static int pl011_startup(struct uart_port *port)
 {
 	struct uart_amba_port *uap =
 	    container_of(port, struct uart_amba_port, port);
-	unsigned int cr, lcr_h, fbrd, ibrd;
+	unsigned int cr;
 	int retval;
 
 	retval = pl011_hwinit(port);
@@ -1595,30 +1617,8 @@ static int pl011_startup(struct uart_port *port)
 
 	writew(uap->vendor->ifls, uap->port.membase + UART011_IFLS);
 
-	/*
-	 * Provoke TX FIFO interrupt into asserting. Taking care to preserve
-	 * baud rate and data format specified by FBRD, IBRD and LCRH as the
-	 * UART may already be in use as a console.
-	 */
 	spin_lock_irq(&uap->port.lock);
 
-	fbrd = readw(uap->port.membase + UART011_FBRD);
-	ibrd = readw(uap->port.membase + UART011_IBRD);
-	lcr_h = readw(uap->port.membase + uap->lcrh_rx);
-
-	cr = UART01x_CR_UARTEN | UART011_CR_TXE | UART011_CR_LBE;
-	writew(cr, uap->port.membase + UART011_CR);
-	writew(0, uap->port.membase + UART011_FBRD);
-	writew(1, uap->port.membase + UART011_IBRD);
-	pl011_write_lcr_h(uap, 0);
-	writew(0, uap->port.membase + UART01x_DR);
-	while (readw(uap->port.membase + UART01x_FR) & UART01x_FR_BUSY)
-		barrier();
-
-	writew(fbrd, uap->port.membase + UART011_FBRD);
-	writew(ibrd, uap->port.membase + UART011_IBRD);
-	pl011_write_lcr_h(uap, lcr_h);
-
 	/* restore RTS and DTR */
 	cr = uap->old_cr & (UART011_CR_RTS | UART011_CR_DTR);
 	cr |= UART01x_CR_UARTEN | UART011_CR_RXE | UART011_CR_TXE;
-- 
1.7.10.4

[PATCH v3, tty-next.. 0/2] serial/amba-pl011: Activate TX IRQ passively

[Dave Martin]

(Based on git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
tty-next (caa445d))

The current PL011 driver transmits a dummy character when the UART
is opened, to assert the TX IRQ for the first time
(see pl011_startup()).  The UART is put in loopback mode temporarily,
so the receiver presumably shouldn't see anything.

However...

At least some platforms containing a PL011 send characters down the
wire even when loopback mode is enabled.  This means that a
spurious NUL character may be seen at the receiver when the PL011 is
opened through the TTY layer.

The current code also temporarily sets the baud rate to maximum and
the character width to the minimum, to that the dummy TX completes
as quickly as possible.  If this is seen by the receiver it will
result in a framing error and can knock the receiver out of sync --
turning subsequent output into garbage until synchronisation
is reestablished.  (Particularly problematic during boot with systemd.)

To avoid spurious transmissions, this patch removes assumptions about
whether the TX IRQ will fire until the FIFO has been filled.

This should also mean that the driver works on the SBSA Generic
UART[1] (a cut-down PL011) without invasive changes.  The Generic
UART lacks some features needed for the dummy TX approach to work
(FIFO disabling and loopback).

[1] Server Base System Architecture (ARM-DEN-0029-v2.3)
    http://infocenter.arm.com/
    (click-thru required :/)

Dave Martin (2):
  Revert "serial/amba-pl011: Leave the TX IRQ alone when the UART is
    not open"
  serial/amba-pl011: Activate TX IRQ passively

 drivers/tty/serial/amba-pl011.c |  118 +++++++++------------------------------
 1 file changed, 27 insertions(+), 91 deletions(-)

-- 
1.7.10.4

[PATCH v3, tty-next.. 1/2] Revert "serial/amba-pl011: Leave the TX IRQ alone when the UART is not open"

[Dave Martin]

This reverts commit f2ee6dfa0e8597eea8b98d240b0033994e20d215.

Jakub Kici?ski observed that this patch can cause the pl011
driver to hang if if the only process with a pl011 port open is
killed by a signal, pl011_shutdown() can get called with an
arbitrary amount of data still in the FIFO.

Calling _shutdown() with the TX FIFO non-empty is questionable
behaviour and my itself be a bug.

Since the affected patch was speculative anyway, and brings limited
benefit, the simplest course is to remove the assumption that TXIS
will always be left asserted after the port is shut down.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
---
 drivers/tty/serial/amba-pl011.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 5a4e9d5..6f5a072 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1639,6 +1639,9 @@ static int pl011_startup(struct uart_port *port)
 
 	writew(uap->vendor->ifls, uap->port.membase + UART011_IFLS);
 
+	/* Assume that TX IRQ doesn't work until we see one: */
+	uap->tx_irq_seen = 0;
+
 	spin_lock_irq(&uap->port.lock);
 
 	/* restore RTS and DTR */
@@ -1702,7 +1705,7 @@ static void pl011_shutdown(struct uart_port *port)
 	spin_lock_irq(&uap->port.lock);
 	uap->im = 0;
 	writew(uap->im, uap->port.membase + UART011_IMSC);
-	writew(0xffff & ~UART011_TXIS, uap->port.membase + UART011_ICR);
+	writew(0xffff, uap->port.membase + UART011_ICR);
 	spin_unlock_irq(&uap->port.lock);
 
 	pl011_dma_shutdown(uap);
-- 
1.7.10.4

[PATCH v3, tty-next.. 2/2] serial/amba-pl011: Activate TX IRQ passively

[Dave Martin]

The current PL011 driver transmits a dummy character when the UART
is opened, to assert the TX IRQ for the first time
(see pl011_startup()).  The UART is put in loopback mode temporarily,
so the receiver presumably shouldn't see anything.

However...

At least some platforms containing a PL011 send characters down the
wire even when loopback mode is enabled.  This means that a
spurious NUL character may be seen at the receiver when the PL011 is
opened through the TTY layer.

The current code also temporarily sets the baud rate to maximum and
the character width to the minimum, to that the dummy TX completes
as quickly as possible.  If this is seen by the receiver it will
result in a framing error and can knock the receiver out of sync --
turning subsequent output into garbage until synchronisation
is reestablished.  (Particularly problematic during boot with systemd.)

To avoid spurious transmissions, this patch removes assumptions about
whether the TX IRQ will fire until the FIFO has been filled.

This should also mean that the driver works on the SBSA Generic
UART[1] (a cut-down PL011) without invasive changes.  The Generic
UART lacks some features needed for the dummy TX approach to work
(FIFO disabling and loopback).

[1] Server Base System Architecture (ARM-DEN-0029-v2.3)
    http://infocenter.arm.com/
    (click-thru required :/)

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
---
 drivers/tty/serial/amba-pl011.c |  119 +++++++++------------------------------
 1 file changed, 26 insertions(+), 93 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 6f5a072..f5bd842 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -58,7 +58,6 @@
 #include <linux/pinctrl/consumer.h>
 #include <linux/sizes.h>
 #include <linux/io.h>
-#include <linux/workqueue.h>
 
 #define UART_NR			14
 
@@ -157,9 +156,7 @@ struct uart_amba_port {
 	unsigned int		lcrh_tx;	/* vendor-specific */
 	unsigned int		lcrh_rx;	/* vendor-specific */
 	unsigned int		old_cr;		/* state during shutdown */
-	struct delayed_work	tx_softirq_work;
 	bool			autorts;
-	unsigned int		tx_irq_seen;	/* 0=none, 1=1, 2=2 or more */
 	char			type[12];
 #ifdef CONFIG_DMA_ENGINE
 	/* DMA stuff */
@@ -1172,15 +1169,14 @@ static void pl011_stop_tx(struct uart_port *port)
 	pl011_dma_tx_stop(uap);
 }
 
-static bool pl011_tx_chars(struct uart_amba_port *uap);
+static void pl011_tx_chars(struct uart_amba_port *uap, bool from_irq);
 
 /* Start TX with programmed I/O only (no DMA) */
 static void pl011_start_tx_pio(struct uart_amba_port *uap)
 {
 	uap->im |= UART011_TXIM;
 	writew(uap->im, uap->port.membase + UART011_IMSC);
-	if (!uap->tx_irq_seen)
-		pl011_tx_chars(uap);
+	pl011_tx_chars(uap, false);
 }
 
 static void pl011_start_tx(struct uart_port *port)
@@ -1247,87 +1243,54 @@ __acquires(&uap->port.lock)
 	spin_lock(&uap->port.lock);
 }
 
-/*
- * Transmit a character
- * There must be at least one free entry in the TX FIFO to accept the char.
- *
- * Returns true if the FIFO might have space in it afterwards;
- * returns false if the FIFO definitely became full.
- */
-static bool pl011_tx_char(struct uart_amba_port *uap, unsigned char c)
+static bool pl011_tx_char(struct uart_amba_port *uap, unsigned char c,
+			  bool from_irq)
 {
+	if (unlikely(!from_irq) &&
+	    readw(uap->port.membase + UART01x_FR) & UART01x_FR_TXFF)
+		return false; /* unable to transmit character */
+
 	writew(c, uap->port.membase + UART01x_DR);
 	uap->port.icount.tx++;
 
-	if (likely(uap->tx_irq_seen > 1))
-		return true;
-
-	return !(readw(uap->port.membase + UART01x_FR) & UART01x_FR_TXFF);
+	return true;
 }
 
-static bool pl011_tx_chars(struct uart_amba_port *uap)
+static void pl011_tx_chars(struct uart_amba_port *uap, bool from_irq)
 {
 	struct circ_buf *xmit = &uap->port.state->xmit;
-	int count;
-
-	if (unlikely(uap->tx_irq_seen < 2))
-		/*
-		 * Initial FIFO fill level unknown: we must check TXFF
-		 * after each write, so just try to fill up the FIFO.
-		 */
-		count = uap->fifosize;
-	else /* tx_irq_seen >= 2 */
-		/*
-		 * FIFO initially at least half-empty, so we can simply
-		 * write half the FIFO without polling TXFF.
-
-		 * Note: the *first* TX IRQ can still race with
-		 * pl011_start_tx_pio(), which can result in the FIFO
-		 * being fuller than expected in that case.
-		 */
-		count = uap->fifosize >> 1;
-
-	/*
-	 * If the FIFO is full we're guaranteed a TX IRQ at some later point,
-	 * and can't transmit immediately in any case:
-	 */
-	if (unlikely(uap->tx_irq_seen < 2 &&
-		     readw(uap->port.membase + UART01x_FR) & UART01x_FR_TXFF))
-		return false;
+	int count = uap->fifosize >> 1;
 
 	if (uap->port.x_char) {
-		pl011_tx_char(uap, uap->port.x_char);
+		if (!pl011_tx_char(uap, uap->port.x_char, from_irq))
+			return;
 		uap->port.x_char = 0;
 		--count;
 	}
 	if (uart_circ_empty(xmit) || uart_tx_stopped(&uap->port)) {
 		pl011_stop_tx(&uap->port);
-		goto done;
+		return;
 	}
 
 	/* If we are using DMA mode, try to send some characters. */
 	if (pl011_dma_tx_irq(uap))
-		goto done;
+		return;
 
-	while (count-- > 0 && pl011_tx_char(uap, xmit->buf[xmit->tail])) {
-		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-		if (uart_circ_empty(xmit))
+	do {
+		if (likely(from_irq) && count-- == 0)
 			break;
-	}
+
+		if (!pl011_tx_char(uap, xmit->buf[xmit->tail], from_irq))
+			break;
+
+		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
+	} while (!uart_circ_empty(xmit));
 
 	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
 		uart_write_wakeup(&uap->port);
 
-	if (uart_circ_empty(xmit)) {
+	if (uart_circ_empty(xmit))
 		pl011_stop_tx(&uap->port);
-		goto done;
-	}
-
-	if (unlikely(!uap->tx_irq_seen))
-		schedule_delayed_work(&uap->tx_softirq_work, uap->port.timeout);
-
-done:
-	return false;
 }
 
 static void pl011_modem_status(struct uart_amba_port *uap)
@@ -1354,28 +1317,6 @@ static void pl011_modem_status(struct uart_amba_port *uap)
 	wake_up_interruptible(&uap->port.state->port.delta_msr_wait);
 }
 
-static void pl011_tx_softirq(struct work_struct *work)
-{
-	struct delayed_work *dwork = to_delayed_work(work);
-	struct uart_amba_port *uap =
-		container_of(dwork, struct uart_amba_port, tx_softirq_work);
-
-	spin_lock(&uap->port.lock);
-	while (pl011_tx_chars(uap)) ;
-	spin_unlock(&uap->port.lock);
-}
-
-static void pl011_tx_irq_seen(struct uart_amba_port *uap)
-{
-	if (likely(uap->tx_irq_seen > 1))
-		return;
-
-	uap->tx_irq_seen++;
-	if (uap->tx_irq_seen < 2)
-		/* first TX IRQ */
-		cancel_delayed_work(&uap->tx_softirq_work);
-}
-
 static irqreturn_t pl011_int(int irq, void *dev_id)
 {
 	struct uart_amba_port *uap = dev_id;
@@ -1414,10 +1355,8 @@ static irqreturn_t pl011_int(int irq, void *dev_id)
 			if (status & (UART011_DSRMIS|UART011_DCDMIS|
 				      UART011_CTSMIS|UART011_RIMIS))
 				pl011_modem_status(uap);
-			if (status & UART011_TXIS) {
-				pl011_tx_irq_seen(uap);
-				pl011_tx_chars(uap);
-			}
+			if (status & UART011_TXIS)
+				pl011_tx_chars(uap, true);
 
 			if (pass_counter-- == 0)
 				break;
@@ -1639,9 +1578,6 @@ static int pl011_startup(struct uart_port *port)
 
 	writew(uap->vendor->ifls, uap->port.membase + UART011_IFLS);
 
-	/* Assume that TX IRQ doesn't work until we see one: */
-	uap->tx_irq_seen = 0;
-
 	spin_lock_irq(&uap->port.lock);
 
 	/* restore RTS and DTR */
@@ -1697,8 +1633,6 @@ static void pl011_shutdown(struct uart_port *port)
 	    container_of(port, struct uart_amba_port, port);
 	unsigned int cr;
 
-	cancel_delayed_work_sync(&uap->tx_softirq_work);
-
 	/*
 	 * disable all interrupts
 	 */
@@ -2245,7 +2179,6 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
 	uap->port.ops = &amba_pl011_pops;
 	uap->port.flags = UPF_BOOT_AUTOCONF;
 	uap->port.line = i;
-	INIT_DELAYED_WORK(&uap->tx_softirq_work, pl011_tx_softirq);
 
 	/* Ensure interrupts from this UART are masked and cleared */
 	writew(0, uap->port.membase + UART011_IMSC);
-- 
1.7.10.4

[PATCH v3 0/*] serial/amba-pl011: Activate TX IRQ passively

[Greg Kroah-Hartman]

On Wed, Mar 25, 2015 at 06:22:26PM +0000, Dave Martin wrote:
> Thanks to Jakub Kici?ski for his bug report and discussion, and for
> showing out how we can manage without the softirq (and providing a
> patch, though merging my rework with it got difficult, so I don't
> include it in the series now).
> 
> 
> There are two alternate versions of the series threaded from this cover
> letter:
> 
>  * [PATCH v3] - patch against v4.0-rc5 that supersedes the previous
>         series; this is the less churny option.
> 
>  * [PATCH v3, tty-next..] - patches against tty-next that
>         modify/partially revert the previous series without needing a
>         rebase.
> 
> Take your pick.

I have no idea what you want me to do here, sorry.

I need to apply patches to tty-next, I can't do anything against a
"clean" 4.0-rc5 as your patches are already in tty-next.

And I can't tell the two series apart here...

Can you just resend what you want me to apply to tty-next and we can go
from there?

confused,

greg k-h

[PATCH v3 0/*] serial/amba-pl011: Activate TX IRQ passively

[Dave Martin]

On Thu, Mar 26, 2015 at 10:30:14PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Mar 25, 2015 at 06:22:26PM +0000, Dave Martin wrote:

[...]

> > Take your pick.
> 
> I have no idea what you want me to do here, sorry.
> 
> I need to apply patches to tty-next, I can't do anything against a
> "clean" 4.0-rc5 as your patches are already in tty-next.
> 
> And I can't tell the two series apart here...
> 
> Can you just resend what you want me to apply to tty-next and we can go
> from there?

Apologies, this was a misguided attempt on my part to be helpful.

I will post a v4 shortly, which changes nothing except for rebasing to
tty-next and clarifying the commit message on the second patch.

Note that I haven't seen any feedback from rmk since v1 (which, for
good reasons, he wasn't keen on).

I believe these patches resolve all issues reported so far by other
testers.

Cheers
---Dave

[PATCH v3 0/*] serial/amba-pl011: Activate TX IRQ passively

[Russell King - ARM Linux]

On Fri, Mar 27, 2015 at 02:51:34PM +0000, Dave Martin wrote:
> Note that I haven't seen any feedback from rmk since v1 (which, for
> good reasons, he wasn't keen on).

Yea, I'm really struggling dealing with email; I can spend an entire day
on email and feel like I've made zero progress without having touched the
kernel source once.  It will be totally random which emails I reply to.
I've long since given up using any Cc or To as an indication whether it's
important, that's too unreliable.

This month, 1/7th of all email received has not even been read... and
some of that's stuff I've thought "I really need to look back at that."

There's just too much irrelevant email coming into my mailbox.

Sorry.

-- 
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.

[PATCH v3 0/*] serial/amba-pl011: Activate TX IRQ passively

[Dave P Martin]

On Fri, Mar 27, 2015 at 08:47:54PM +0000, Russell King - ARM Linux wrote:

[...]
 
> This month, 1/7th of all email received has not even been read... and
> some of that's stuff I've thought "I really need to look back at that."
> 
> There's just too much irrelevant email coming into my mailbox.
> 
> Sorry.

No worries, I just wanted didn't want Greg to infer that you'd given
your opinion already.

Cheers
---Dave