On 7 November 2011 16:18, Javi Merino <javi.merino@xxxxxxx> wrote: > On 05/11/11 19:05, Thomas Abraham wrote: >> Hi Javi, >> >> On 6 October 2011 05:10, Javi Merino <javi.merino@xxxxxxx> wrote: >>> If two requests have been submitted and one of them is running, if you >>> call pl330_chan_ctrl(ch_id, PL330_OP_START), there's a window of time >>> between the spin_lock_irqsave() and the _state() check in which the >>> running transaction may finish. In that case, we don't receive the >>> interrupt (because they are disabled), but _start() sees that the DMA >>> is stopped, so it starts it. The problem is that it sends the >>> transaction that has just finished again, because pl330_update() >>> hasn't mark it as done yet. >>> >>> This patch fixes this race condition by not calling _start() if the >>> DMA is already executing transactions. When interrupts are reenabled, >>> pl330_update() will call _start(). >>> >>> Signed-off-by: Javi Merino <javi.merino@xxxxxxx> >>> Acked-by: Jassi Brar <jassi.brar@xxxxxxxxxxx> >>> --- >>> arch/arm/common/pl330.c | 2 +- >>> 1 files changed, 1 insertions(+), 1 deletions(-) >>> >>> diff --git a/arch/arm/common/pl330.c b/arch/arm/common/pl330.c >>> index 97912fa..7129cfb 100644 >>> --- a/arch/arm/common/pl330.c >>> +++ b/arch/arm/common/pl330.c >>> @@ -1546,7 +1546,7 @@ int pl330_chan_ctrl(void *ch_id, enum pl330_chan_op op) >>> >>> /* Start the next */ >>> case PL330_OP_START: >>> - if (!_start(thrd)) >>> + if (!_thrd_active(thrd) && !_start(thrd)) >>> ret = -EIO; >>> break; >> >> On Samsung's Exynos4 platform, while testing audio playback with i2s >> interface, the above change causes the playback to freeze. The >> _thrd_active(thrd) call always returns '1' and hence _start(thrd) is >> not getting called. > > If _thrd_active(thrd) returns '1', that means there is an active > transfer still running or, if it has finished, you haven't called > pl330_update() to acknowledge that. pl330_update() calls _start() as > soon as it can. > > drivers/dma/pl330.c registers the irq handler in pl330_probe(), so when > the transaction finishes, pl330_update() should clear it and call > _start(). If there is any outstanding transaction, it should start > straight away. If there isn't, it would mark the channel as free, so > _thrd_active() should return '0'. If _thrd_active() is still '1', then > something has gone wrong in the way. > > Does this shed some light? Thanks for the detailed explanation. I will check again on the lines you have mentioned above. Also, the i2s audio playback on exynos had been working prior to this change. So that might imply that pl330_update was working as you have mentioned. Anyway, I will check again. Thanks, Thomas. > > Cheers, > Javi > > -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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