From: joelf@ti•com (Joel Fernandes)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 7/9] ARM: edma: Don't clear EMR of channel in edma_stop
Date: Wed, 31 Jul 2013 00:05:15 -0500 [thread overview]
Message-ID: <51F89B0B.4080803@ti.com> (raw)
In-Reply-To: <51F77982.7030601@ti.com>
On 07/30/2013 03:29 AM, Sekhar Nori wrote:
> On Monday 29 July 2013 06:59 PM, Joel Fernandes wrote:
>> We certainly don't want error conditions to be cleared anywhere
>
> 'anywhere' is a really loaded term.
>
>> as this will make us 'forget' about missed events. We depend on
>> knowing which events were missed in order to be able to reissue them.
>
>> This fixes a race condition where the EMR was being cleared
>> by the transfer completion interrupt handler.
>>
>> Basically, what was happening was:
>>
>> Missed event
>> |
>> |
>> V
>> SG1-SG2-SG3-Null
>> \
>> \__TC Interrupt (Almost same time as ARM is executing
>> TC interrupt handler, an event got missed and also forgotten
>> by clearing the EMR).
>
> Sorry, but I dont see how edma_stop() is coming into picture in the race
> you describe?
In edma_callback function, for the case of DMA_COMPLETE (Transfer
completion interrupt), edma_stop() is called when all sets have been
processed. This had the effect of clearing the EMR.
This has 2 problems:
1.
If error interrupt is also pending and TC interrupt clears the EMR.
Due to this the ARM will execute the error interrupt even though the EMR
is clear. As a result, the following if condition in dma_ccerr_handler
will be true and IRQ_NONE is returned.
if ((edma_read_array(ctlr, EDMA_EMR, 0) == 0) &&
(edma_read_array(ctlr, EDMA_EMR, 1) == 0) &&
(edma_read(ctlr, EDMA_QEMR) == 0) &&
(edma_read(ctlr, EDMA_CCERR) == 0))
return IRQ_NONE;
If this happens enough number of times, IRQ subsystem disables the
interrupt thinking its spurious which creates serious problems.
2.
If the above if statement condition is removed, then EMR is 0 so the
callback function will not be called in dma_ccerr_handler thus the event
is forgotten, never triggered manually or never sets missed flag of the
channel.
So about the race: TC interrupt handler executing before the error
interrupt handler can result in clearing the EMR and creates these problems.
>> The EMR is ultimately being cleared by the Error interrupt
>> handler once it is handled so we don't have to do it in edma_stop.
>
> This, I agree with. edma_clean_channel() also there to re-initialize the
> channel so doing it in edma_stop() certainly seems superfluous.
Sure.
Thanks,
-Joel
next prev parent reply other threads:[~2013-07-31 5:05 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-29 13:29 [PATCH 0/9] dma: edma: Support scatter-lists of any length Joel Fernandes
2013-07-29 13:29 ` [PATCH 1/9] dma: edma: Setup parameters to DMA MAX_NR_SG at a time Joel Fernandes
2013-07-29 13:29 ` [PATCH 2/9] dma: edma: Write out and handle MAX_NR_SG at a given time Joel Fernandes
2013-07-29 13:29 ` [PATCH 3/9] ARM: edma: Add function to manually trigger an EDMA channel Joel Fernandes
2013-07-30 5:18 ` Sekhar Nori
2013-07-31 4:30 ` Joel Fernandes
2013-07-31 5:23 ` Sekhar Nori
2013-07-31 5:34 ` Fernandes, Joel
2013-07-29 13:29 ` [PATCH 4/9] dma: edma: Find missed events and issue them Joel Fernandes
2013-07-30 7:05 ` Sekhar Nori
2013-07-31 4:49 ` Joel Fernandes
2013-07-31 9:18 ` Sekhar Nori
2013-08-01 2:27 ` Joel Fernandes
2013-08-01 3:43 ` Joel Fernandes
2013-08-01 4:39 ` Joel Fernandes
2013-08-01 6:13 ` Sekhar Nori
2013-08-01 20:28 ` Joel Fernandes
2013-08-01 20:48 ` Joel Fernandes
2013-08-02 13:26 ` Sekhar Nori
2013-08-02 18:15 ` Joel Fernandes
2013-08-02 23:00 ` Joel Fernandes
2013-07-29 13:29 ` [PATCH 5/9] dma: edma: Leave linked to Null slot instead of DUMMY slot Joel Fernandes
2013-07-29 13:29 ` [PATCH 6/9] dma: edma: Detect null slot errors and handle them correctly Joel Fernandes
2013-07-29 13:29 ` [PATCH 7/9] ARM: edma: Don't clear EMR of channel in edma_stop Joel Fernandes
2013-07-30 8:29 ` Sekhar Nori
2013-07-31 5:05 ` Joel Fernandes [this message]
2013-07-31 9:35 ` Sekhar Nori
2013-08-01 1:59 ` Joel Fernandes
2013-07-29 13:29 ` [PATCH 8/9] dma: edma: Link to dummy slot only for last SG list split Joel Fernandes
2013-07-29 13:29 ` [PATCH 9/9] dma: edma: remove limits on number of slots Joel Fernandes
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