From: javi.merino@arm•com (Javi Merino)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v2] ARM: pl330: Fix a race condition
Date: Mon, 07 Nov 2011 10:48:58 +0000 [thread overview]
Message-ID: <4EB7B79A.2020004@arm.com> (raw)
In-Reply-To: <CAJuYYwTXf-XU0fdGT0+sggN-MEY3v7UHkfjNkM4+QUW464J9Ew@mail.gmail.com>
On 05/11/11 19:05, Thomas Abraham wrote:
> Hi Javi,
>
> On 6 October 2011 05:10, Javi Merino <javi.merino@arm•com> 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@arm•com>
>> Acked-by: Jassi Brar <jassi.brar@samsung•com>
>> ---
>> 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
next prev parent reply other threads:[~2011-11-07 10:48 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-19 17:11 [PATCH] ARM: pl330: Fix a race condition Javi Merino
2011-09-19 18:07 ` Jassi Brar
2011-09-20 13:36 ` Javi Merino
2011-10-05 12:57 ` Javi Merino
2011-10-06 9:10 ` [PATCH v2] " Javi Merino
2011-11-05 19:05 ` Thomas Abraham
2011-11-07 10:48 ` Javi Merino [this message]
2011-11-07 11:03 ` Thomas Abraham
2011-11-28 8:23 ` Boojin Kim
2011-11-28 16:36 ` Javi Merino
2011-11-29 3:41 ` Boojin Kim
2011-11-29 9:53 ` Javi Merino
2011-11-29 10:37 ` Jassi Brar
2011-12-07 7:52 ` Kukjin Kim
2011-12-07 10:01 ` Javi Merino
2011-12-07 20:54 ` Javi Merino
2011-12-09 11:58 ` Javi Merino
2011-12-09 13:04 ` Jassi Brar
2011-12-09 13:41 ` Javi Merino
2011-12-09 14:15 ` Jassi Brar
2011-12-09 14:52 ` Javi Merino
2011-12-09 16:50 ` Jassi Brar
2011-12-09 19:50 ` Javi Merino
2011-12-11 10:51 ` Jassi Brar
2011-12-11 15:09 ` Javi Merino
2011-12-11 17:10 ` Jassi Brar
2011-12-11 17:42 ` Javi Merino
2011-12-11 19:27 ` [PATCH] ARM: PL330: Fix driver freeze Javi Merino
2011-12-15 17:48 ` Javi Merino
2011-12-16 9:01 ` Tushar Behera
2011-12-16 6:27 ` Jassi Brar
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