From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from lb3-smtp-cloud3.xs4all.net ([194.109.24.30]:35228 "EHLO lb3-smtp-cloud3.xs4all.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754102AbcDVObe (ORCPT ); Fri, 22 Apr 2016 10:31:34 -0400 Subject: Re: [PATCH] media: vb2: Fix regression on poll() for RW mode To: Mauro Carvalho Chehab References: <1461230116-6909-1-git-send-email-ricardo.ribalda@gmail.com> <5719EC8D.2000500@xs4all.nl> <20160422093141.7f9191bc@recife.lan> <571A1AF3.3040507@xs4all.nl> <20160422112136.06afe7c3@recife.lan> Cc: Ricardo Ribalda Delgado , Pawel Osciak , Marek Szyprowski , Kyungmin Park , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, Junghak Sung , stable@vger.kernel.org From: Hans Verkuil Message-ID: <571A35C0.8020900@xs4all.nl> Date: Fri, 22 Apr 2016 16:31:28 +0200 MIME-Version: 1.0 In-Reply-To: <20160422112136.06afe7c3@recife.lan> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: On 04/22/2016 04:21 PM, Mauro Carvalho Chehab wrote: > Em Fri, 22 Apr 2016 14:37:07 +0200 > Hans Verkuil escreveu: > >> On 04/22/2016 02:31 PM, Mauro Carvalho Chehab wrote: >>> Em Fri, 22 Apr 2016 11:19:09 +0200 >>> Hans Verkuil escreveu: >>> >>>> Hi Ricardo, >>>> >>>> On 04/21/2016 11:15 AM, Ricardo Ribalda Delgado wrote: >>>>> When using a device is read/write mode, vb2 does not handle properly the >>>>> first select/poll operation. It allways return POLLERR. >>>>> >>>>> 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 by poll, due to a previous check. >>>>> >>>>> Reported-by: Dimitrios Katsaros >>>>> Cc: Junghak Sung >>>>> Cc: stable@vger.kernel.org >>>>> Fixes: 49d8ab9feaf2 ("media] media: videobuf2: Separate vb2_poll()") >>>>> Signed-off-by: Ricardo Ribalda Delgado >>>>> --- >>>>> drivers/media/v4l2-core/videobuf2-core.c | 8 ++++++++ >>>>> drivers/media/v4l2-core/videobuf2-v4l2.c | 8 -------- >>>>> 2 files changed, 8 insertions(+), 8 deletions(-) >>>>> >>>>> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c >>>>> index 5d016f496e0e..199c65dbe330 100644 >>>>> --- a/drivers/media/v4l2-core/videobuf2-core.c >>>>> +++ b/drivers/media/v4l2-core/videobuf2-core.c >>>>> @@ -2298,6 +2298,14 @@ 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. >>>>> + */ >>>>> + if (q->waiting_for_buffers && (req_events & (POLLIN | POLLRDNORM))) >>>>> + return POLLERR; >>>> >>>> The problem I have with this is that this should be specific to V4L2. The only >>>> reason we do this is that we had to stay backwards compatible with vb1. >>>> >>>> This is the reason this code was placed in videobuf2-v4l2.c. But you are correct >>>> that this causes a regression, and I see no other choice but to put it in core.c. >>>> >>>> That said, I would still only honor this when called from v4l2, so I suggest that >>>> a new flag 'check_waiting_for_buffers' is added that is only set in vb2_queue_init >>>> in videobuf2-v4l2.c. >>>> >>>> So the test above becomes: >>>> >>>> if (q->check_waiting_for_buffers && q->waiting_for_buffers && >>>> (req_events & (POLLIN | POLLRDNORM))) >>>> >>>> It's not ideal, but at least this keeps this v4l2 specific. >>> >>> I don't like the above approach, for two reasons: >>> >>> 1) it is not obvious that this is V4L2 specific from the code; >> >> s/check_waiting_for_buffers/v4l2_needs_to_wait_for_buffers/ > > Better, but still hell of a hack. Maybe we could add a quirks > flag and add a flag like: > VB2_FLAG_ENABLE_POLLERR_IF_WAITING_BUFFERS_AND_NO_QBUF > (or some better naming, I'm not inspired today...) > > Of course, such quirk should be properly documented. How about 'quirk_poll_must_check_waiting_for_buffers'? Something with 'quirk' in the name is a good idea. > >>> >>> 2) we should not mess the core due to some V4L2 mess. >> >> Well, the only other alternative I see is to split vb2_core_poll() into two >> since the check has to happen in the middle. The v4l2 code would call core_poll1(), >> then do the check and afterwards call core_poll2(). And that would really be ugly. > > Actually, the first callback would be better called as > vb2_core_poll_check() - or something with similar name. > > IMHO, this is the cleaner solution, although it adds an extra cost. I really don't like this. This has a much larger impact on vb2 core then adding a simple quirk flag. Regards, Hans