On Fri, Feb 26, 2016 at 12:23:27PM +0200, Peter Ujfalusi wrote: > On 2016-02-26 03:06, Russell King - ARM Linux wrote: > > On Thu, Feb 25, 2016 at 10:28:59AM +0200, Peter Ujfalusi wrote: > >> When based on the CCR_ENABLE bit the channel is stopped we should not call > >> omap_dma_callback(), only change the return value to DMA_COMPLETE. Client > >> drivers will do the right thing to clean up the channel after the transfer > >> has been completed. > >> Check the CCR_ENABLE only if the channel is not paused since pause in sDMA > >> means that the channel is stopped. > >> This will fix one hard to reproduce race condition when the channel is > >> terminated during transfer (affecting cyclic operation). > >> > >> Fixes: 1a7cf7b26f25 ("dmaengine: omap-dma: Handle cases when the channel is polled for completion") > >> > >> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@xxxxxx> > >> --- > >> drivers/dma/omap-dma.c | 16 ++++++++++------ > >> 1 file changed, 10 insertions(+), 6 deletions(-) > >> > >> diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c > >> index f6bef0d93998..a6b189fdbbe6 100644 > >> --- a/drivers/dma/omap-dma.c > >> +++ b/drivers/dma/omap-dma.c > >> @@ -671,18 +671,22 @@ static enum dma_status omap_dma_tx_status(struct dma_chan *chan, > >> struct omap_chan *c = to_omap_dma_chan(chan); > >> struct virt_dma_desc *vd; > >> enum dma_status ret; > >> - uint32_t ccr; > >> unsigned long flags; > >> > >> - ccr = omap_dma_chan_read(c, CCR); > >> - /* The channel is no longer active, handle the completion right away */ > >> - if (!(ccr & CCR_ENABLE)) > >> - omap_dma_callback(c->dma_ch, 0, c); > >> - > >> ret = dma_cookie_status(chan, cookie, txstate); > >> if (ret == DMA_COMPLETE || !txstate) > >> return ret; > >> > >> + if (!c->paused) { > >> + uint32_t ccr = omap_dma_chan_read(c, CCR); > >> + /* > >> + * The channel is no longer active, set the return value > >> + * accordingly > >> + */ > >> + if (!(ccr & CCR_ENABLE)) > >> + ret = DMA_COMPLETE; > >> + } > >> + > > > > This looks very much like a hack, and surely opens a race condition > > up: what happens when a request submitted and pending but not yet > > started? If the channel is idle, requesting status will report > > that the request has completed. > > > > It's also wrong for another reason. If txstate is NULL... > > True, I have fixed these up. > > > Your original commit adding the original hack that you're now removing > > above says that this is to support polled operation: I'm not aware of > > DMA engine supporting such a mode. DMA_PREP_INTERRUPT is a mechanism > > where requests can be queued without an interrupt to allow batching. > > Also it is used to suppress DMA interrupts during audio playback for example. > In this case we will run w/o interrupts and the position is polled. > > > See the raid5/async_tx code, which queues a set of operations without > > DMA_PREP_INTERRUPT, with the final operation with DMA_PREP_INTERRUPT > > set. > > We only allow the interrupts to be disabled in cyclic or memcpy mode. With > slave_sg we have interrupts as it is needed to move to the next SG. > > > As the driver is reliant on interrupts to move to the next transfer, > > the patch which causes DMA_PREP_INTERRUPT to influence whether > > interrupts are sent is actually buggy, and will prevent several > > queued DMA operations to fail. > > Yes, the omap-dma only allows the interrupts to be actually disabled when it > is save to do so. slave_sg can not work w/o interrupts so there we don't > disable them. I get the impression that you haven't taken in what I've said, because each fragment of your reply is just repeating what the previous fragment said. Let me state that I don't believe you need any hacks here, and this patch is not necessary: the final operation in a set of chained memcpy()s should have DMA_PREP_INTERRUPT set. For the periodic stuff for audio, it's irrelevant anyway: periodic transfers never complete - you can start them, and they continue running until terminated. There's no completion. -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html