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From: Scott Branden <sbranden@broadcom.com>
To: Vinod Koul <vinod.koul@intel.com>, Jassi Brar <jassisinghbrar@gmail.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	ismail <ismail@broadcom.com>, Anatol Pomazao <anatol@google.com>,
	Dmitry Torokhov <dtor@google.com>,
	<bcm-kernel-feedback-list@broadcom.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] dmaengine: pl330: fix the race condition in pl330 driver.
Date: Mon, 30 Mar 2015 20:40:43 -0700	[thread overview]
Message-ID: <551A173B.4010704@broadcom.com> (raw)
In-Reply-To: <20150330172546.GI7192@intel.com>

Hi Vinod, Jassi,

Some details on the problem encountered.

On 15-03-30 10:25 AM, Vinod Koul wrote:
> On Mon, Mar 30, 2015 at 10:17:17PM +0530, Jassi Brar wrote:
>> On Fri, Mar 27, 2015 at 5:25 AM, Scott Branden <sbranden@broadcom.com> wrote:
>>> From: ismail <ismail@broadcom.com>
>>>
>>> Update the thread running index before issuing the
>>> GO command to the DMAC.
>>>
>>> Tested-by: Mohamed Ismail Abdul Packir Mohamed <ismail@broadcom.com>
>>> Reviewed-by: Ray Jui <rjui@broadcom.com>
>>> Reviewed-by: Arun Parameswaran <aparames@broadcom.com>
>>> Reviewed-by: Scott Branden <sbranden@broadcom.com>
>>> Signed-off-by: Scott Branden <sbranden@broadcom.com>
>>> Signed-off-by: Mohamed Ismail Abdul Packir Mohamed <ismail@broadcom.com>
>>> ---
>>>   drivers/dma/pl330.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
>>> index 0e1f567..631642d 100644
>>> --- a/drivers/dma/pl330.c
>>> +++ b/drivers/dma/pl330.c
>>> @@ -1072,11 +1072,11 @@ static bool _trigger(struct pl330_thread *thrd)
>>>          /* Set to generate interrupts for SEV */
>>>          writel(readl(regs + INTEN) | (1 << thrd->ev), regs + INTEN);
>>>
>>> +       thrd->req_running = idx;
>>> +
>>>          /* Only manager can execute GO */
>>>          _execute_DBGINSN(thrd, insn, true);
>>>
>>> -       thrd->req_running = idx;
>>> -
>> It would help to know what the behavior looks like before and after
>> the patch. If anything we should look at locking rather the
>> reordering.
> Yes that ia fair request, looking at changelog it is hard to understand the
> issue seen?
>
We encountered this problem as we modified the driver to make SMC calls 
to a TZ handler.  This slowed down the driver to the point where DMA 
transactions easily failed.  I believe the same could be accomplished by 
adding a delay between the GOCMD and update of the req_running and 
running the built in dmatest.

The DMA transaction is broken if the interrupt occurs before the 
thrd->req_running is updated.

The pl330 issues a GOCMD (in _trigger function) to start a new transfer.

The issue of GOCMD generates an interrupt and the IRQ handler will call 
the pl330_update function to process the interrupt.

The pl330_update function will verify the thread running index and break 
the transaction, if the thread running index is not set.

Regards,
  Scott



  reply	other threads:[~2015-03-31  3:40 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-26 23:55 Scott Branden
2015-03-29 21:55 ` Scott Branden
2015-03-30 16:47 ` Jassi Brar
2015-03-30 17:25   ` Vinod Koul
2015-03-31  3:40     ` Scott Branden [this message]
2015-03-31  5:20       ` Jassi Brar
2015-03-31 22:04         ` Scott Branden

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