On 10/10/16 15:07, Vignesh R wrote: > From: Sebastian Andrzej Siewior <[email protected]> > > 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.
Acked-by: Peter Ujfalusi <[email protected]> > v2…v3: > - rephrase the comment based on Russell's information / feedback. > > v1…v2: > - move the drain loop into omap_dma_drain_chan() instead of having it > twice. > - allow pause only for DMA_DEV_TO_MEM transfers if non-cyclic. Add a > comment why DMA_MEM_TO_DEV not allowed. > - clear pause on terminate_all. Otherwise pause() + terminate_all() > will keep the pause bit set and we can't pause the following > transfer. > > Signed-off-by: Sebastian Andrzej Siewior <[email protected]> > [[email protected]: drain channel only when buffering is on, rebase to v4.8] > Signed-off-by: Vignesh R <[email protected]> > --- > > Link to v3: https://patchwork.kernel.org/patch/6972961/ > > drivers/dma/omap-dma.c | 124 > +++++++++++++++++++++++++++++++++++-------------- > 1 file changed, 89 insertions(+), 35 deletions(-) > > diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c > index 1b7f5f32bf74..93a01c4eb479 100644 > --- a/drivers/dma/omap-dma.c > +++ b/drivers/dma/omap-dma.c > @@ -422,7 +422,30 @@ static void omap_dma_start(struct omap_chan *c, struct > omap_desc *d) > c->running = true; > } > > -static void omap_dma_stop(struct omap_chan *c) > +static void omap_dma_drain_chan(struct omap_chan *c) > +{ > + int i; > + u32 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; > @@ -435,7 +458,6 @@ 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; > @@ -446,27 +468,19 @@ 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); > + if (!(c->ccr & CCR_BUFFERING_DISABLE)) > + 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); > + > + if (!(c->ccr & CCR_BUFFERING_DISABLE)) > + omap_dma_drain_chan(c); > } > > mb(); > @@ -481,8 +495,8 @@ static void omap_dma_stop(struct omap_chan *c) > > omap_dma_chan_write(c, CLNK_CTRL, val); > } > - > c->running = false; > + return 0; > } > > static void omap_dma_start_sg(struct omap_chan *c, struct omap_desc *d) > @@ -836,6 +850,8 @@ 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; > @@ -1244,10 +1260,8 @@ static int omap_dma_terminate_all(struct dma_chan > *chan) > omap_dma_stop(c); > } > > - if (c->cyclic) { > - c->cyclic = false; > - c->paused = false; > - } > + c->cyclic = false; > + c->paused = false; > > vchan_get_all_descriptors(&c->vc, &head); > spin_unlock_irqrestore(&c->vc.lock, flags); > @@ -1266,28 +1280,66 @@ static void omap_dma_synchronize(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; > + bool can_pause; > > - /* 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->desc) > + goto out; > + > + if (c->cyclic) > + can_pause = 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). > + */ > + 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 */ > @@ -1295,9 +1347,11 @@ 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
