On 08/03/2015 12:54 PM, Sebastian Andrzej Siewior wrote: > On 08/03/2015 06:34 PM, Peter Hurley wrote: >> Hi Sebastian, > > Hi Peter, > >>> struct old_serial_port { >>> diff --git a/drivers/tty/serial/8250/8250_omap.c >>> b/drivers/tty/serial/8250/8250_omap.c >>> index d9a37191a1ae..12249125a218 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; >>> @@ -256,18 +256,6 @@ 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); >>> @@ -309,6 +297,7 @@ 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. >>> @@ -322,6 +311,7 @@ static void omap_8250_set_termios(struct uart_port >>> *port, >>> struct omap8250_priv *priv = up->port.private_data; >>> unsigned char cval = 0; >>> unsigned int baud; >>> + unsigned int complete_dma = 0; >>> >>> switch (termios->c_cflag & CSIZE) { >>> case CS5: >>> @@ -473,6 +463,25 @@ static void omap_8250_set_termios(struct uart_port >>> *port, >>> if (termios->c_iflag & IXANY) >>> up->mcr |= UART_MCR_XONANY; >>> } >>> + >>> + if (up->dma && up->dma->tx_running) { >>> + struct uart_8250_dma *dma = up->dma; >>> + >>> + /* >>> + * 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 happen. >>> + */ >>> + >>> + dma->tx_running = 2; >>> + >>> + spin_unlock_irq(&up->port.lock); >>> + wait_event(priv->termios_wait, >>> + dma->tx_running == 3); >> >> Doesn't the dmaengine api offer a race-free way to wait for pending tx dma >> to complete? > > Not that I know of. You still need to ensure that once that DMA > completed, nobody triggers another TX transfer before you do what you > planned. This is ensures by the tx_running != 0 and the spin lock. > >> Maybe we could wrap that in the 8250 dma api? > > You mean a function in 8250-dma API which does what I did just here > with the wait_event() and the wake_up in the callback? That way I could > move the termios_wait into the dma struct instead of keeping in the > omap specific part. I am also not sure if OMAP is the only one that may > hang here or the other people just didn't notice it yet.
Exactly; and we need to fix DMA wrt x_char anyway. Going back to the dmaengine api, I think something like this might work (as a first approximation): dma_sync_wait(dma->txchan, dma->tx_cookie); dmaengine_pause(dma->txchan); /* remainder of set_termios */ dmaengine_resume(dma->txchan); We could require 8250 core dma to support pause/resume. >>> + spin_lock_irq(&up->port.lock); >>> + complete_dma = 1; >>> + } >>> omap8250_restore_regs(up); >>> >>> spin_unlock_irq(&up->port.lock); >>> @@ -488,6 +497,8 @@ 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 */ >>> @@ -869,17 +880,18 @@ 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); >>> >>> @@ -899,7 +911,7 @@ 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); >>> } >>> >>> @@ -1216,6 +1228,7 @@ 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; >>> > > Sebastian > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/