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Date: Mon, 4 Apr 2016 21:07:04 -0700
From: Peter Hurley <peter@...leysoftware.com>
To: John Ogness <john.ogness@...utronix.de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Tony Lindgren <tony@...mide.com>, nsekhar@...com,
linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
linux-omap@...r.kernel.org
Subject: Re: [PATCH] tty: serial: 8250_omap: do not defer termios changes
On 03/31/2016 01:41 AM, John Ogness wrote:
> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
>
> It has been observed that the TX-DMA can stall
Does this happen on any other OMAP part besides am335x?
I looked back over the LKML history of this and didn't see any other
design implicated in this problem.
> if termios changes
> occur while a TX-DMA operation is in progress. Previously this was
> handled by allowing set_termios to return immediately and deferring
> the change until the operation is completed. Now set_termios will
> block until the operation is completed, proceed with the changes,
> then schedule any pending next operation.
I ask because I wonder if this is related to the tx dma trigger
problem (worked around by writing a byte to the tx fifo on am335x)?
If so, then
1) It should use the OMAP_DMA_TX_KICK bug flag
2) It could pause dma, complete set_termios(), then resume dma which would
keep everything nice and linear.
Or even just drop DMA for the am335x and only use the normal 8250_dma
support for newer OMAP designs.
Regards,
Peter Hurley
> Commit message and forward port by John Ogness.
>
> Tested-by: John Ogness <john.ogness@...utronix.de>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
> Patch against next-20160331.
>
> drivers/tty/serial/8250/8250_omap.c | 57 ++++++++++++++++----------
> 1 file changed, 37 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index 6f76051..9459b4d 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -100,9 +100,9 @@ struct omap8250_priv {
> u8 wer;
> u8 xon;
> u8 xoff;
> - u8 delayed_restore;
> u16 quot;
>
> + wait_queue_head_t termios_wait;
> bool is_suspending;
> int wakeirq;
> int wakeups_enabled;
> @@ -257,18 +257,6 @@ static void omap8250_update_mdr1(struct uart_8250_port *up,
> static void omap8250_restore_regs(struct uart_8250_port *up)
> {
> struct omap8250_priv *priv = up->port.private_data;
> - struct uart_8250_dma *dma = up->dma;
> -
> - if (dma && dma->tx_running) {
> - /*
> - * TCSANOW requests the change to occur immediately however if
> - * we have a TX-DMA operation in progress then it has been
> - * observed that it might stall and never complete. Therefore we
> - * delay DMA completes to prevent this hang from happen.
> - */
> - priv->delayed_restore = 1;
> - return;
> - }
>
> serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
> serial_out(up, UART_EFR, UART_EFR_ECB);
> @@ -310,6 +298,7 @@ static void omap8250_restore_regs(struct uart_8250_port *up)
> up->port.ops->set_mctrl(&up->port, up->port.mctrl);
> }
>
> +static void omap_8250_dma_tx_complete(void *param);
> /*
> * OMAP can use "CLK / (16 or 13) / div" for baud rate. And then we have have
> * some differences in how we want to handle flow control.
> @@ -320,6 +309,8 @@ static void omap_8250_set_termios(struct uart_port *port,
> {
> struct uart_8250_port *up = up_to_u8250p(port);
> struct omap8250_priv *priv = up->port.private_data;
> + struct uart_8250_dma *dma = up->dma;
> + unsigned int complete_dma = 0;
> unsigned char cval = 0;
> unsigned int baud;
>
> @@ -430,7 +421,7 @@ static void omap_8250_set_termios(struct uart_port *port,
> priv->scr = OMAP_UART_SCR_RX_TRIG_GRANU1_MASK | OMAP_UART_SCR_TX_EMPTY |
> OMAP_UART_SCR_TX_TRIG_GRANU1_MASK;
>
> - if (up->dma)
> + if (dma)
> priv->scr |= OMAP_UART_SCR_DMAMODE_1 |
> OMAP_UART_SCR_DMAMODE_CTL;
>
> @@ -460,6 +451,24 @@ static void omap_8250_set_termios(struct uart_port *port,
> priv->efr |= OMAP_UART_SW_TX;
> }
> }
> +
> + if (dma && dma->tx_running) {
> + /*
> + * TCSANOW requests the change to occur immediately, however
> + * if we have a TX-DMA operation in progress then it has been
> + * observed that it might stall and never complete. Therefore
> + * we wait until DMA completes to prevent this hang from
> + * happening.
> + */
> +
> + dma->tx_running = 2;
> +
> + spin_unlock_irq(&up->port.lock);
> + wait_event_interruptible(priv->termios_wait,
> + dma->tx_running == 3);
> + spin_lock_irq(&up->port.lock);
> + complete_dma = 1;
> + }
> omap8250_restore_regs(up);
>
> spin_unlock_irq(&up->port.lock);
> @@ -475,6 +484,8 @@ static void omap_8250_set_termios(struct uart_port *port,
> /* Don't rewrite B0 */
> if (tty_termios_baud_rate(termios))
> tty_termios_encode_baud_rate(termios, baud, baud);
> + if (complete_dma)
> + omap_8250_dma_tx_complete(up);
> }
>
> /* same as 8250 except that we may have extra flow bits set in EFR */
> @@ -893,17 +904,18 @@ static void omap_8250_dma_tx_complete(void *param)
>
> spin_lock_irqsave(&p->port.lock, flags);
>
> + if (dma->tx_running == 2) {
> + dma->tx_running = 3;
> + wake_up(&priv->termios_wait);
> + goto out;
> + }
> +
> dma->tx_running = 0;
>
> xmit->tail += dma->tx_size;
> xmit->tail &= UART_XMIT_SIZE - 1;
> p->port.icount.tx += dma->tx_size;
>
> - if (priv->delayed_restore) {
> - priv->delayed_restore = 0;
> - omap8250_restore_regs(p);
> - }
> -
> if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
> uart_write_wakeup(&p->port);
>
> @@ -923,7 +935,7 @@ static void omap_8250_dma_tx_complete(void *param)
> p->ier |= UART_IER_THRI;
> serial_port_out(&p->port, UART_IER, p->ier);
> }
> -
> +out:
> spin_unlock_irqrestore(&p->port.lock, flags);
> }
>
> @@ -1088,6 +1100,10 @@ static inline int omap_8250_rx_dma(struct uart_8250_port *p, unsigned int iir)
> {
> return -EINVAL;
> }
> +
> +static void omap_8250_dma_tx_complete(void *param)
> +{
> +}
> #endif
>
> static int omap8250_no_handle_irq(struct uart_port *port)
> @@ -1241,6 +1257,7 @@ static int omap8250_probe(struct platform_device *pdev)
> priv->omap8250_dma.rx_size = RX_TRIGGER;
> priv->omap8250_dma.rxconf.src_maxburst = RX_TRIGGER;
> priv->omap8250_dma.txconf.dst_maxburst = TX_TRIGGER;
> + init_waitqueue_head(&priv->termios_wait);
>
> if (of_machine_is_compatible("ti,am33xx"))
> priv->habit |= OMAP_DMA_TX_KICK;
>
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