On 08/07/2015 11:00 PM, Sebastian Andrzej Siewior wrote:
> -static void omap_dma_stop(struct omap_chan *c)
> +static void omap_dma_drain_chan(struct omap_chan *c)
> +{
> + int i;
> + uint32_t val;
> +
> + /* Wait for sDMA FIFO to drain */
> + for (i = 0; ; i++) {
> + val = omap_dma_chan_read(c, CCR);
> + if (!(val & (CCR_RD_ACTIVE | CCR_WR_ACTIVE)))
> + break;
> +
> + if (i > 100)
> + break;
> +
> + udelay(5);
> + }
> +
> + if (val & (CCR_RD_ACTIVE | CCR_WR_ACTIVE))
> + dev_err(c->vc.chan.device->dev,
> + "DMA drain did not complete on lch %d\n",
> + c->dma_ch);
> +}
> +
> +static int omap_dma_stop(struct omap_chan *c)
> {
> struct omap_dmadev *od = to_omap_dma_dev(c->vc.chan.device);
> uint32_t val;
> @@ -312,7 +335,6 @@ static void omap_dma_stop(struct omap_chan *c)
> val = omap_dma_chan_read(c, CCR);
> if (od->plat->errata & DMA_ERRATA_i541 && val & CCR_TRIGGER_SRC) {
> uint32_t sysconfig;
> - unsigned i;
>
> sysconfig = omap_dma_glbl_read(od, OCP_SYSCONFIG);
> val = sysconfig & ~DMA_SYSCONFIG_MIDLEMODE_MASK;
> @@ -323,27 +345,18 @@ static void omap_dma_stop(struct omap_chan *c)
> val &= ~CCR_ENABLE;
> omap_dma_chan_write(c, CCR, val);
>
> - /* Wait for sDMA FIFO to drain */
> - for (i = 0; ; i++) {
> - val = omap_dma_chan_read(c, CCR);
> - if (!(val & (CCR_RD_ACTIVE | CCR_WR_ACTIVE)))
> - break;
> -
> - if (i > 100)
> - break;
> -
> - udelay(5);
> - }
> -
> - if (val & (CCR_RD_ACTIVE | CCR_WR_ACTIVE))
> - dev_err(c->vc.chan.device->dev,
> - "DMA drain did not complete on lch %d\n",
> - c->dma_ch);
> + omap_dma_drain_chan(c);
>
> omap_dma_glbl_write(od, OCP_SYSCONFIG, sysconfig);
> } else {
> +
> + if (!(val & CCR_ENABLE))
> + return -EINVAL;
> +
> val &= ~CCR_ENABLE;
> omap_dma_chan_write(c, CCR, val);
> +
> + omap_dma_drain_chan(c);
Note that the FIFO drain only applies to source synchronized transfers... When
the BUFFERING is _not_ disabled - in most of the cases this is true.
> + /*
> + * We do not allow DMA_MEM_TO_DEV transfers to be paused.
> + * From the AM572x TRM, 16.1.4.18 Disabling a Channel During Transfer:
> + * "When a channel is disabled during a transfer, the channel undergoes
> + * an abort, unless it is hardware-source-synchronized …".
> + * A source-synchronised channel is one where the fetching of data is
> + * under control of the device. In other words, a device-to-memory
> + * transfer. So, a destination-synchronised channel (which would be a
> + * memory-to-device transfer) undergoes an abort if the the CCR_ENABLE
> + * bit is cleared.
> + * From 16.1.4.20.4.6.2 Abort: "If an abort trigger occurs, the channel
> + * aborts immediately after completion of current read/write
> + * transactions and then the FIFO is cleaned up." The term "cleaned up"
> + * is not defined. TI recommends to check that RD_ACTIVE and WR_ACTIVE
> + * are both clear _before_ disabling the channel, otherwise data loss
> + * will occur.
> + * The problem is that if the channel is active, then device activity
> + * can result in DMA activity starting between reading those as both
> + * clear and the write to DMA_CCR to clear the enable bit hitting the
> + * hardware. If the DMA hardware can't drain the data in its FIFO to the
> + * destination, then data loss "might" occur (say if we write to an UART
> + * and the UART is not accepting any further data).
I don't know if you have checked it, but probably the TX DMA could be also
used when the PRZEFETCH is disabled for the channel? Just a guess
> + */
> + else if (c->desc->dir == DMA_DEV_TO_MEM)
> + can_pause = true;
> +
> + if (can_pause && !c->paused) {
> + ret = omap_dma_stop(c);
> + if (!ret)
> + c->paused = true;
> }
> +out:
> + spin_unlock_irqrestore(&od->irq_lock, flags);
>
> - return 0;
> + 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 +1134,11 @@ 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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