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Date: Mon, 25 Apr 2016 10:56:24 +0200
From: Hans Verkuil <hverkuil@...all.nl>
To: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
Pawel Osciak <pawel@...iak.com>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Kyungmin Park <kyungmin.park@...sung.com>,
Mauro Carvalho Chehab <mchehab@....samsung.com>,
linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Junghak Sung <jh1009.sung@...sung.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2] media: vb2: Fix regression on poll() for RW mode
On 04/25/2016 10:39 AM, Hans Verkuil wrote:
> On 04/25/2016 09:59 AM, Ricardo Ribalda Delgado wrote:
>> When using a device is read/write mode, vb2 does not handle properly the
>> first select/poll operation.
>>
>> The reason for this, is that when this code has been refactored, some of
>> the operations have changed their order, and now fileio emulator is not
>> started.
>>
>> The reintroduced check to the core is enabled by a quirk flag, that
>> avoids this check by other subsystems like DVB.
>>
>> Reported-by: Dimitrios Katsaros <patcherwork@...il.com>
>> Cc: Junghak Sung <jh1009.sung@...sung.com>
>> Fixes: 49d8ab9feaf2 ("media] media: videobuf2: Separate vb2_poll()")
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
>> ---
>>
>> v2: By Hans Verkuil <hverkuil@...all.nl> and
>> Mauro Carvalho Chehab <mchehab@....samsung.com>:
>>
>> Add a quirk bit to enable this behaviour on the core.
>> drivers/media/v4l2-core/videobuf2-core.c | 9 +++++++++
>> drivers/media/v4l2-core/videobuf2-v4l2.c | 9 +--------
>> include/media/videobuf2-core.h | 4 ++++
>> 3 files changed, 14 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
>> index 5d016f496e0e..58eb9be13510 100644
>> --- a/drivers/media/v4l2-core/videobuf2-core.c
>> +++ b/drivers/media/v4l2-core/videobuf2-core.c
>> @@ -2298,6 +2298,15 @@ unsigned int vb2_core_poll(struct vb2_queue *q, struct file *file,
>> return POLLERR;
>>
>> /*
>> + * For compatibility with vb1: if QBUF hasn't been called yet, then
>> + * return POLLERR as well. This only affects capture queues, output
>> + * queues will always initialize waiting_for_buffers to false.
>> + */
>
> This comment should be moved to where the quirk is set in v4l2. This comment shouldn't
> refer to vb2 at all. How about:
I'm sorry, I realize I was quite confusing here. I should have said:
"This comment should be copied to where the quirk is set in v4l2. This comment here
in core.c shouldn't refer to vb1 at all. How about:"
So in both places (here and in v4l2.c) there should be a comment.
Can you make a v4? Ask on irc if something is still unclear.
Hans
>
> "If this quirk is set and if QBUF hasn't been called..."
>
> and perhaps at the end of the comment:
>
> "This quirk is set by V4L2 for backwards compatibility reasons."
>
> although I am not completely certain we need that at all here.
>
>> + if (q->quirk_poll_must_check_waiting_for_buffers &&
>> + q->waiting_for_buffers && (req_events & (POLLIN | POLLRDNORM)))
>> + return POLLERR;
>> +
>> + /*
>> * For output streams you can call write() as long as there are fewer
>> * buffers queued than there are buffers available.
>> */
>> diff --git a/drivers/media/v4l2-core/videobuf2-v4l2.c b/drivers/media/v4l2-core/videobuf2-v4l2.c
>> index 91f552124050..3e649adf85ef 100644
>> --- a/drivers/media/v4l2-core/videobuf2-v4l2.c
>> +++ b/drivers/media/v4l2-core/videobuf2-v4l2.c
>> @@ -765,6 +765,7 @@ int vb2_queue_init(struct vb2_queue *q)
>> q->is_output = V4L2_TYPE_IS_OUTPUT(q->type);
>> q->copy_timestamp = (q->timestamp_flags & V4L2_BUF_FLAG_TIMESTAMP_MASK)
>> == V4L2_BUF_FLAG_TIMESTAMP_COPY;
>> + q->quirk_poll_must_check_waiting_for_buffers = true;
>>
>> return vb2_core_queue_init(q);
>> }
>> @@ -818,14 +819,6 @@ unsigned int vb2_poll(struct vb2_queue *q, struct file *file, poll_table *wait)
>> poll_wait(file, &fh->wait, wait);
>> }
>>
>> - /*
>> - * For compatibility with vb1: if QBUF hasn't been called yet, then
>> - * return POLLERR as well. This only affects capture queues, output
>> - * queues will always initialize waiting_for_buffers to false.
>> - */
>> - if (q->waiting_for_buffers && (req_events & (POLLIN | POLLRDNORM)))
>> - return POLLERR;
>> -
>> return res | vb2_core_poll(q, file, wait);
>> }
>> EXPORT_SYMBOL_GPL(vb2_poll);
>> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
>> index 8a0f55b6c2ba..3a1620946068 100644
>> --- a/include/media/videobuf2-core.h
>> +++ b/include/media/videobuf2-core.h
>> @@ -400,6 +400,9 @@ struct vb2_buf_ops {
>> * @fileio_read_once: report EOF after reading the first buffer
>> * @fileio_write_immediately: queue buffer after each write() call
>> * @allow_zero_bytesused: allow bytesused == 0 to be passed to the driver
>> + * @quirk_poll_must_check_waiting_for_buffers: Return POLLERR at poll when QBUF
>> + * has not been called. This is a vb1 idiom that has been adopted
>> + * also by vb2.
>> * @lock: pointer to a mutex that protects the vb2_queue struct. The
>> * driver can set this to a mutex to let the v4l2 core serialize
>> * the queuing ioctls. If the driver wants to handle locking
>> @@ -463,6 +466,7 @@ struct vb2_queue {
>> unsigned fileio_read_once:1;
>> unsigned fileio_write_immediately:1;
>> unsigned allow_zero_bytesused:1;
>> + unsigned quirk_poll_must_check_waiting_for_buffers:1;
>>
>> struct mutex *lock;
>> void *owner;
>>
>
> Regards,
>
> Hans
> --
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