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From: heikki.krogerus@linux.intel.com (Heikki Krogerus)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx
Date: Thu, 11 Sep 2014 14:17:21 +0300
Message-ID: <20140911111721.GB17476@xps8300> (raw)
In-Reply-To: <1410377411-26656-10-git-send-email-bigeasy@linutronix.de>

On Wed, Sep 10, 2014 at 09:30:04PM +0200, Sebastian Andrzej Siewior wrote:
> At least on AM335x the following problem exists: Even if the TX FIFO is
> empty and a TX transfer is programmed (and started) the UART does not
> trigger the DMA transfer.
> After $TRESHOLD number of bytes have been written to the FIFO manually the
> UART reevaluates the whole situation and decides that now there is enough
> room in the FIFO and so the transfer begins.
> This problem has not been seen on DRA7 or beagle board xm (OMAP3). I am not
> sure if this is UART-IP core specific or DMA engine.
> 
> The workaround is to use a threshold of one byte, program the DMA
> transfer minus one byte and then to put the first byte into the FIFO to
> kick start the transfer.
> 
> v7?v8:
> 	- fix the problem when get invoked and the FIFO is full.
> 
> Reviewed-by: Tony Lindgren <tony@atomide.com>
> Tested-by: Tony Lindgren <tony@atomide.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  drivers/tty/serial/8250/8250.h     |  3 +++
>  drivers/tty/serial/8250/8250_dma.c | 39 +++++++++++++++++++++++++++++++++++---
>  include/uapi/linux/serial_reg.h    |  1 +
>  3 files changed, 40 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
> index fbed1636e9c4..09489b391568 100644
> --- a/drivers/tty/serial/8250/8250.h
> +++ b/drivers/tty/serial/8250/8250.h
> @@ -82,6 +82,9 @@ struct serial8250_config {
>  #define UART_BUG_PARITY	(1 << 4)	/* UART mishandles parity if FIFO enabled */
>  #define UART_BUG_DMA_RX	(1 << 5)	/* UART needs DMA RX req before there is
>  					   data in FIFO */
> +#define UART_BUG_DMA_TX	(1 << 6)	/* UART needs one byte in FIFO for
> +					   kickstart */

I don't think we should go ahead with this patch. I'm pretty sure
this is AM335 specific problem, or at least limited to only few
platforms. And I don't think we should take any more "BUG" flags.

We should add hooks like tx_dma and rx_dma to struct uart_8250_dma so
that the probe drivers can replace serial8250_tx_dma and
seria8250_rx_dma, like I think Alan already suggested.

Let's keep serial8250_tx_dma/rx_dma as the default, and not add any
quirks to them. Only if there is a very common case should it be
handled in those. The case of RX req needing to be sent before data in
FIFO maybe one of those, but I'm no sure.


>  #define PROBE_RSA	(1 << 0)
>  #define PROBE_ANY	(~0)
>  
> diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
> index 3674900a1f14..48dc57aad0dd 100644
> --- a/drivers/tty/serial/8250/8250_dma.c
> +++ b/drivers/tty/serial/8250/8250_dma.c
> @@ -83,6 +83,7 @@ int serial8250_tx_dma(struct uart_8250_port *p)
>  	struct uart_8250_dma		*dma = p->dma;
>  	struct circ_buf			*xmit = &p->port.state->xmit;
>  	struct dma_async_tx_descriptor	*desc;
> +	unsigned int			skip_byte = 0;
>  	int ret;
>  
>  	if (uart_tx_stopped(&p->port) || dma->tx_running ||
> @@ -91,10 +92,40 @@ int serial8250_tx_dma(struct uart_8250_port *p)
>  
>  	dma->tx_size = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
>  
> +	if (p->bugs & UART_BUG_DMA_TX) {
> +		u8 tx_lvl;
> +
> +		/*
> +		 * We need to put the first byte into the FIFO in order to start
> +		 * the DMA transfer. For transfers smaller than four bytes we
> +		 * don't bother doing DMA at all. It seem not matter if there
> +		 * are still bytes in the FIFO from the last transfer (in case
> +		 * we got here directly from __dma_tx_complete()). Bytes leaving
> +		 * the FIFO seem not to trigger the DMA transfer. It is really
> +		 * the byte that we put into the FIFO.
> +		 * If the FIFO is already full then we most likely got here from
> +		 * __dma_tx_complete(). And this means the DMA engine just
> +		 * completed its work. We don't have to wait the complete 86us
> +		 * at 115200,8n1 but around 60us (not to mention lower
> +		 * baudrates). So in that case we take the interrupt and try
> +		 * again with an empty FIFO.
> +		 */
> +		tx_lvl = serial_in(p, UART_OMAP_TX_LVL);
> +		if (tx_lvl == p->tx_loadsz) {
> +			ret = -EBUSY;
> +			goto err;
> +		}
> +		if (dma->tx_size < 4) {
> +			ret = -EINVAL;
> +			goto err;
> +		}
> +		skip_byte = 1;
> +	}
> +
>  	desc = dmaengine_prep_slave_single(dma->txchan,
> -					   dma->tx_addr + xmit->tail,
> -					   dma->tx_size, DMA_MEM_TO_DEV,
> -					   DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
> +			dma->tx_addr + xmit->tail + skip_byte,
> +			dma->tx_size - skip_byte, DMA_MEM_TO_DEV,
> +			DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
>  	if (!desc) {
>  		ret = -EBUSY;
>  		goto err;
> @@ -118,6 +149,8 @@ int serial8250_tx_dma(struct uart_8250_port *p)
>  			serial_out(p, UART_IER, p->ier);
>  		}
>  	}
> +	if (skip_byte)
> +		serial_out(p, UART_TX, xmit->buf[xmit->tail]);
>  	return 0;
>  err:
>  	dma->tx_err = 1;
> diff --git a/include/uapi/linux/serial_reg.h b/include/uapi/linux/serial_reg.h
> index df6c9ab6b0cd..53af3b790129 100644
> --- a/include/uapi/linux/serial_reg.h
> +++ b/include/uapi/linux/serial_reg.h
> @@ -359,6 +359,7 @@
>  #define UART_OMAP_SYSC		0x15	/* System configuration register */
>  #define UART_OMAP_SYSS		0x16	/* System status register */
>  #define UART_OMAP_WER		0x17	/* Wake-up enable register */
> +#define UART_OMAP_TX_LVL	0x1a	/* TX FIFO level register */
>  
>  /*
>   * These are the definitions for the MDR1 register
> -- 
> 2.1.0

Cheers,

-- 
heikki

  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 [this message]
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 ` [PATCH 10/16] tty: serial: 8250_dma: optimize the xmit path due to UART_BUG_DMA_TX Sebastian Andrzej Siewior
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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