linux-kernel - RE: [PATCH 1/2] omap3: ISP: Fix the failure of CCDC capture during suspend/resume

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Date:	Wed, 7 Sep 2011 15:40:23 +0530
From:	"Koyamangalath, Abhilash" <abhilash.kv@...com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	"Ravi, Deepthy" <deepthy.ravi@...com>
CC:	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mchehab@...radead.org" <mchehab@...radead.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: RE: [PATCH 1/2] omap3: ISP: Fix the failure of CCDC capture during
 suspend/resume



On Tue, Aug 30, 2011  Laurent Pinchart wrote:
> Hi,
>
> On Wednesday 10 August 2011 16:03:12 Deepthy Ravi wrote:
>> From: Abhilash K V <abhilash.kv@...com>
>>
>> While resuming from the "suspended to memory" state,
>> occasionally CCDC fails to get enabled and thus fails
>> to capture frames any more till the next suspend/resume
>> is issued.
>> This is a race condition which happens only when a CCDC
>> frame-completion ISR is pending even as ISP device's
>> isp_pm_prepare() is getting called and only one buffer
>> is left on the DMA queue.
>> The DMA queue buffers are thus depleted which results in
>> its underrun.So when ISP resumes there are no buffers on
>> the queue (as the application which can issue buffers is
>> yet to resume) to start video capture.
>> This fix addresses this issue by dequeuing and enqueing
>> the last buffer in isp_pm_prepare() after its DMA gets
>> completed. Thus,when ISP resumes it always finds atleast
>> one buffer on the DMA queue - this is true if application
>> uses only 3 buffers.
>
> How is that problem specific to the CCDC ? Can't it be reproduce at the
> preview engine or resizer output as well ?
[Abhilash K V]Yes,  I believe this issue would crop with preview and resizer too though I have
not been able to try these out.
>
> --
> Regards,
>
> Laurent Pinchart
>

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