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? 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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