linux-kernel - Re: [PATCH 1/1] videobuf: Initialize lists in videobuf

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Message-ID: <79f17a04986247b4ac5806e708f3d2d5.squirrel@webmail.xs4all.nl>
Date:	Wed, 17 Nov 2010 13:44:57 +0100
From:	"Hans Verkuil" <hverkuil@...all.nl>
To:	"Laurent Pinchart" <laurent.pinchart@...asonboard.com>
Cc:	"Andrew Chew" <achew@...dia.com>,
	"'Figo.zhang'" <zhangtianfei@...dcoretech.com>,
	"pawel@...iak.com" <pawel@...iak.com>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] videobuf: Initialize lists in videobuf_buffer.


> Hi Hans,
>
> On Wednesday 17 November 2010 08:11:06 Hans Verkuil wrote:
>> On Wednesday, November 17, 2010 02:38:09 Andrew Chew wrote:
>> > > > diff --git a/drivers/media/video/videobuf-dma-contig.c
>> > >
>> > > b/drivers/media/video/videobuf-dma-contig.c
>> > >
>> > > > index c969111..f7e0f86 100644
>> > > > --- a/drivers/media/video/videobuf-dma-contig.c
>> > > > +++ b/drivers/media/video/videobuf-dma-contig.c
>> > > > @@ -193,6 +193,8 @@ static struct videobuf_buffer
>> > >
>> > > *__videobuf_alloc_vb(size_t size)
>> > >
>> > > >   	if (vb) {
>> > > >
>> > > >   		mem = vb->priv = ((char *)vb) + size;
>> > > >   		mem->magic = MAGIC_DC_MEM;
>> > > >
>> > > > +		INIT_LIST_HEAD(&vb->stream);
>> > > > +		INIT_LIST_HEAD(&vb->queue);
>> > >
>> > > i think it no need to be init, it just a list-entry.
>> >
>> > Okay, if that's really the case, then sh_mobile_ceu_camera.c,
>> > pxa_camera.c, mx1_camera.c, mx2_camera.c, and omap1_camera.c needs to
>> be
>> > fixed to remove that WARN_ON(!list_empty(&vb->queue)); in their
>> > videobuf_prepare() methods, because those WARN_ON's are assuming that
>> > vb->queue is properly initialized as a list head.
>> >
>> > Which will it be?
>>
>> These list entries need to be inited. It is bad form to have
>> uninitialized
>> list entries. It is not as if this is a big deal to initialize them
>> properly.
>
> I disagree with that. List heads must be initialized, but there's no point
> in
> initializing list entries.

You are right. I got confused due to some problems I had in the past in
another driver, but it turned out to be a list header that caused the
problems, not a list entry. So removing the bogus WARN_ONs is sufficient.

Regards,

       Hans

-- 
Hans Verkuil - video4linux developer - sponsored by Cisco

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