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Date: Fri, 7 Aug 2015 12:44:01 +0300
From: Peter Ujfalusi <peter.ujfalusi@...com>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Vinod Koul <vinod.koul@...el.com>
CC: Dan Williams <dan.j.williams@...el.com>,
<dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<nsekhar@...com>, <linux-omap@...r.kernel.org>,
<linux-serial@...r.kernel.org>, <john.ogness@...utronix.de>,
Russell King <rmk+kernel@....linux.org.uk>
Subject: Re: [PATCH] dma: omap-dma: add support for pause of non-cyclic
transfers
On 08/07/2015 11:41 AM, Sebastian Andrzej Siewior wrote:
> This DMA driver is used by 8250-omap on DRA7-evm. There is one
> requirement that is to pause a transfer. This is currently used on the RX
> side. It is possible that the UART HW aborted the RX (UART's RX-timeout)
> but the DMA controller starts the transfer shortly after.
> Before we can manually purge the FIFO we need to pause the transfer,
> check how many bytes it already received and terminate the transfer
> without it making any progress.
>
> From testing on the TX side it seems that it is possible that we invoke
> pause once the transfer has completed which is indicated by the missing
> CCR_ENABLE bit but before the interrupt has been noticed. In that case the
> interrupt will come even after disabling it.
>
> The AM572x manual says that we have to wait for the CCR_RD_ACTIVE &
> CCR_WR_ACTIVE bits to be gone before programming it again here is the
> drain loop. Also it looks like without the drain the TX-transfer makes
> sometimes progress.
>
> One note: The pause + resume combo is broken because after resume the
> the complete transfer will be programmed again. That means the already
> transferred bytes (until the pause event) will be sent again. This is
> currently not important for my UART user because it does only pause +
> terminate.
with a short testing audio did not broke (the only user of pause/resume)
Some comments embedded.
> Cc: <stable@...r.kernel.org>
Why stable? This is not fixing any bugs since the PAUSE was not allowed for
non cyclic transfers.
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
> drivers/dma/omap-dma.c | 54 ++++++++++++++++++++++++++++++++++++++------------
> 1 file changed, 41 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c
> index 249445c8a4c6..6b8497203caf 100644
> --- a/drivers/dma/omap-dma.c
> +++ b/drivers/dma/omap-dma.c
> @@ -299,7 +299,7 @@ static void omap_dma_start(struct omap_chan *c, struct omap_desc *d)
> omap_dma_chan_write(c, CCR, d->ccr | CCR_ENABLE);
> }
>
> -static void omap_dma_stop(struct omap_chan *c)
> +static int omap_dma_stop(struct omap_chan *c)
> {
> struct omap_dmadev *od = to_omap_dma_dev(c->vc.chan.device);
> uint32_t val;
> @@ -342,8 +342,26 @@ static void omap_dma_stop(struct omap_chan *c)
>
> omap_dma_glbl_write(od, OCP_SYSCONFIG, sysconfig);
> } else {
> + int i = 0;
> +
> + if (!(val & CCR_ENABLE))
> + return -EINVAL;
> +
> val &= ~CCR_ENABLE;
> omap_dma_chan_write(c, CCR, val);
> + do {
> + val = omap_dma_chan_read(c, CCR);
> + if (!(val & (CCR_RD_ACTIVE | CCR_WR_ACTIVE)))
> + break;
> + if (i > 100)
if (++i > 100)
break;
to avoid infinite loop?
> + break;
> + udelay(5);
> + } while (1);
> +
> + if (val & (CCR_RD_ACTIVE | CCR_WR_ACTIVE))
if (i > 100) ?
> + dev_err(c->vc.chan.device->dev,
> + "DMA drain did not complete on lch %d\n",
> + c->dma_ch);
> }
>
> mb();
> @@ -358,6 +376,7 @@ static void omap_dma_stop(struct omap_chan *c)
>
> omap_dma_chan_write(c, CLNK_CTRL, val);
> }
> + return 0;
> }
>
> static void omap_dma_start_sg(struct omap_chan *c, struct omap_desc *d,
> @@ -728,6 +747,8 @@ static enum dma_status omap_dma_tx_status(struct dma_chan *chan,
> } else {
> txstate->residue = 0;
> }
> + if (ret == DMA_IN_PROGRESS && c->paused)
> + ret = DMA_PAUSED;
> spin_unlock_irqrestore(&c->vc.lock, flags);
>
> return ret;
> @@ -1053,28 +1074,33 @@ static int omap_dma_terminate_all(struct dma_chan *chan)
> static int omap_dma_pause(struct dma_chan *chan)
> {
> struct omap_chan *c = to_omap_dma_chan(chan);
> + struct omap_dmadev *od = to_omap_dma_dev(chan->device);
> + unsigned long flags;
> + int ret = -EINVAL;
>
> - /* Pause/Resume only allowed with cyclic mode */
> - if (!c->cyclic)
> - return -EINVAL;
> + spin_lock_irqsave(&od->irq_lock, flags);
>
> - if (!c->paused) {
> - omap_dma_stop(c);
> - c->paused = true;
> + if (!c->paused && c->desc) {
> + ret = omap_dma_stop(c);
> + if (!ret)
> + c->paused = true;
> }
>
> - return 0;
> + spin_unlock_irqrestore(&od->irq_lock, flags);
> +
> + return ret;
> }
>
> static int omap_dma_resume(struct dma_chan *chan)
> {
> struct omap_chan *c = to_omap_dma_chan(chan);
> + struct omap_dmadev *od = to_omap_dma_dev(chan->device);
> + unsigned long flags;
> + int ret = -EINVAL;
>
> - /* Pause/Resume only allowed with cyclic mode */
> - if (!c->cyclic)
> - return -EINVAL;
> + spin_lock_irqsave(&od->irq_lock, flags);
>
> - if (c->paused) {
> + if (c->paused && c->desc) {
> mb();
>
> /* Restore channel link register */
> @@ -1082,9 +1108,11 @@ static int omap_dma_resume(struct dma_chan *chan)
>
> omap_dma_start(c, c->desc);
> c->paused = false;
> + ret = 0;
> }
> + spin_unlock_irqrestore(&od->irq_lock, flags);
>
> - return 0;
> + return ret;
> }
>
> static int omap_dma_chan_init(struct omap_dmadev *od)
>
--
Péter
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