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

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Message-Id: <201109071236.34883.laurent.pinchart@ideasonboard.com>
Date:	Wed, 7 Sep 2011 12:36:34 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	"Koyamangalath, Abhilash" <abhilash.kv@...com>
Cc:	"Ravi, Deepthy" <deepthy.ravi@...com>,
	"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

Hi,

On Wednesday 07 September 2011 12:10:23 Koyamangalath, Abhilash wrote:
> On Tue, Aug 30, 2011  Laurent Pinchart wrote:
> > 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 ?
> 
> Yes, I believe this issue would crop with preview and resizer too though I
> have not been able to try these out.

That's my belief as well. In that case the fix should be generic, not CCDC-
specific.

-- 
Regards,

Laurent Pinchart
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