linux-kernel - Re: 2.6.30-rc2-git2: Reported regressions from 2.6.29

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Date:	Sat, 18 Apr 2009 11:50:51 +0800
From:	leiming <tom.leiming@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Adrian Bunk <bunk@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Natalie Protasevich <protasnb@...il.com>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	Linux PM List <linux-pm@...ts.linux-foundation.org>,
	Linux SCSI List <linux-scsi@...r.kernel.org>,
	video4linux-list@...hat.com, laurent.pinchart@...net.be,
	mchehab@...radead.org
Subject: Re: 2.6.30-rc2-git2: Reported regressions from 2.6.29

On Fri, 17 Apr 2009 19:55:29 -0700 (PDT)
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> @@ -742,7 +742,7 @@ static int uvc_alloc_urb_buffers(struct
> > uvc_video_device *video, 
> >  	/* Buffers are already allocated, bail out. */
> >  	if (video->urb_size)
> > -		return 0;
> > +		return DIV_ROUND_UP(video->urb_size, psize);
> 
> I don't think this is right. It should round _down_.
> 
> It's supposed to return 'npackets', but if you pass it a different
> packet size than it was passed originally, it can now return a

Now uvc only uses the previous allocated buffer in suspend/resume
path, so the packet size doen't change in this path.

> potentially bigger number than the already allocated buffer, no?

If this case does exist, the URBs need to be updated and the patch is 
not enough. 

> 
> So I think it should round down (ie use a regular divide). No?

Because the following fact:

	uvc_alloc_urb_buffers()
	{
		...
		video->urb_size = psize * npackets; 
		...
	}

so DIV_ROUND_UP still can work correctly.

Thanks!

-- 
Lei Ming
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