[ANN] Call for topics for the media mini-summit on Friday Oct 27 in Prague

[ANN] Call for topics for the media mini-summit on Friday Oct 27 in Prague

[Hans Verkuil]

Hi all,

We are organizing a media mini-summit on Friday October 27 in Prague, co-located
with the ELCE conference:

http://events.linuxfoundation.org/events/embedded-linux-conference-europe

This is a call for topics to discuss during that mini-summit.

Also, if you plan to attend, please let me know. It is open for all, but it is
nice if we know beforehand who we can expect.

So if you have a topic that you want to discuss there, then just reply to this
post. If possible, please add a rough idea of how much time you think you will
need.

I plan to make the agenda based on the received topics around mid-October.

Let me kick this off:

Topic: Media development process: what works, what doesn't.
Purpose: In the past 6 months or so we tried to improve the media development
	 process. This is an overview of what we did and why we did it, what
	 works and what doesn't. Feedback is very much appreciated. It is even
	 more appreciated if people/companies would be willing to assign
	 new developers to help improve the media subsystem!
Duration: 30-60 minutes

Topic: status of the HDMI CEC kernel support.
Purpose: give a quick overview of the status: what has been merged, what is still
	 pending, what is under development.
Duration: 10-15 minutes

Regards,

	Hans

Re: [ANN] Call for topics for the media mini-summit on Friday Oct 27 in Prague

[Ricardo Ribalda Delgado]

Hi Hans

On Fri, Sep 1, 2017 at 11:46 AM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>
>
> Also, if you plan to attend, please let me know. It is open for all, but it is
> nice if we know beforehand who we can expect.
>

I plan to attend. I do not have any specific topic right now, but as
the date gets closer I might add something.

See you in Prague.
Thanks

Re: [ANN] Call for topics for the media mini-summit on Friday Oct 27 in Prague

[Honza Petrouš]

>
> Also, if you plan to attend, please let me know. It is open for all, but it is
> nice if we know beforehand who we can expect.
>
> So if you have a topic that you want to discuss there, then just reply to this
> post. If possible, please add a rough idea of how much time you think you will
> need.
>

Hi Hans,

I'm going to attend LCE, but I still don't know if I will be able to
stay till Friday.
When I know more I drop message.

/Honza

Re: [ANN] Call for topics for the media mini-summit on Friday Oct 27 in Prague

[Alexandre Courbot]

Hi!

On Fri, Sep 1, 2017 at 6:46 PM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
> Hi all,
>
> We are organizing a media mini-summit on Friday October 27 in Prague, co-located
> with the ELCE conference:
>
> http://events.linuxfoundation.org/events/embedded-linux-conference-europe
>
> This is a call for topics to discuss during that mini-summit.
>
> Also, if you plan to attend, please let me know. It is open for all, but it is
> nice if we know beforehand who we can expect.
>
> So if you have a topic that you want to discuss there, then just reply to this
> post. If possible, please add a rough idea of how much time you think you will
> need.

I will be here to discuss the request API:

Topic: request/jobs API
Purpose: overview of the work based on the request API (proposed new
name: jobs API), to hopefully converge to something that can be merged
soon.

I plan to have a concrete, reasonable proposal by then.

Pawel may also attend, but not 100% sure yet.

Looking forward to seeing you all there!

Alex.

Re: [ANN] Call for topics for the media mini-summit on Friday Oct 27 in Prague

[Gustavo Padovan]

Hi Hans,



On Fri, Sep 1, 2017 at 6:46 AM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
> Hi all,
>
> We are organizing a media mini-summit on Friday October 27 in Prague, co-located
> with the ELCE conference:
>
> http://events.linuxfoundation.org/events/embedded-linux-conference-europe
>
> This is a call for topics to discuss during that mini-summit.
>
> Also, if you plan to attend, please let me know. It is open for all, but it is
> nice if we know beforehand who we can expect.
>
> So if you have a topic that you want to discuss there, then just reply to this
> post. If possible, please add a rough idea of how much time you think you will
> need.
>
> I plan to make the agenda based on the received topics around mid-October.
>

I"m attending and I want to propose a discussion:

Topic: V4L2 Explicit Syncronization
Purpose: quick overview and discuss of the API/direction we are going
with fences
Duration: 20-30min

Regards,

Gustavo

Re: [ANN] Call for topics for the media mini-summit on Friday Oct 27 in Prague

[Mauro Carvalho Chehab]

Em Fri, 1 Sep 2017 11:46:59 +0200
Hans Verkuil <hverkuil@xs4all.nl> escreveu:

> Hi all,
> 
> We are organizing a media mini-summit on Friday October 27 in Prague, co-located
> with the ELCE conference:
> 
> http://events.linuxfoundation.org/events/embedded-linux-conference-europe
> 
> This is a call for topics to discuss during that mini-summit.
> 
> Also, if you plan to attend, please let me know. It is open for all, but it is
> nice if we know beforehand who we can expect.
> 
> So if you have a topic that you want to discuss there, then just reply to this
> post. If possible, please add a rough idea of how much time you think you will
> need.
> 
> I plan to make the agenda based on the received topics around mid-October.
> 
> Let me kick this off:
> 
> Topic: Media development process: what works, what doesn't.
> Purpose: In the past 6 months or so we tried to improve the media development
> 	 process. This is an overview of what we did and why we did it, what
> 	 works and what doesn't. Feedback is very much appreciated. It is even
> 	 more appreciated if people/companies would be willing to assign
> 	 new developers to help improve the media subsystem!
> Duration: 30-60 minutes
> 
> Topic: status of the HDMI CEC kernel support.
> Purpose: give a quick overview of the status: what has been merged, what is still
> 	 pending, what is under development.
> Duration: 10-15 minutes


Topic: Media kAPI and uAPI documentation
Purpose: to give the current status of media API and identify possible
	 gaps and how to improve it.

Duration: 45-60 minutes.


Thanks,
Mauro

Re: [ANN] Call for topics for the media mini-summit on Friday Oct 27 in Prague

[Shuah Khan]

Hi Hans/Gustavo.

On Wed, Oct 4, 2017 at 1:34 PM, Gustavo Padovan <gustavo@padovan.org> wrote:
> Hi Hans,
>
>
>
> On Fri, Sep 1, 2017 at 6:46 AM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>> Hi all,
>>
>> We are organizing a media mini-summit on Friday October 27 in Prague, co-located
>> with the ELCE conference:
>>
>> http://events.linuxfoundation.org/events/embedded-linux-conference-europe
>>
>> This is a call for topics to discuss during that mini-summit.
>>
>> Also, if you plan to attend, please let me know. It is open for all, but it is
>> nice if we know beforehand who we can expect.
>>
>> So if you have a topic that you want to discuss there, then just reply to this
>> post. If possible, please add a rough idea of how much time you think you will
>> need.
>>
>> I plan to make the agenda based on the received topics around mid-October.
>>
>
> I"m attending and I want to propose a discussion:
>
> Topic: V4L2 Explicit Syncronization
> Purpose: quick overview and discuss of the API/direction we are going
> with fences
> Duration: 20-30min

I would have loved to attend the Media mini-summit. Unfortunately I
already made plans to leave Friday. In addition participating in the
V4L2 Explicit Syncronization discussion, it would have been good to
discuss:

the my pending Media/Audio resource sharing patch series that is
dependent on Sakari's lifetime managemnet patch series.

I have been unable to get any discussion going on this topic on the
mailing list.

thanks,
-- Shuah

Re: [ANN] Call for topics for the media mini-summit on Friday Oct 27 in Prague

[Hans Verkuil]

Hi Shuah,

On 10/05/2017 03:53 PM, Shuah Khan wrote:
> Hi Hans/Gustavo.
> 
> On Wed, Oct 4, 2017 at 1:34 PM, Gustavo Padovan <gustavo@padovan.org> wrote:
>> Hi Hans,
>>
>>
>>
>> On Fri, Sep 1, 2017 at 6:46 AM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>>> Hi all,
>>>
>>> We are organizing a media mini-summit on Friday October 27 in Prague, co-located
>>> with the ELCE conference:
>>>
>>> http://events.linuxfoundation.org/events/embedded-linux-conference-europe
>>>
>>> This is a call for topics to discuss during that mini-summit.
>>>
>>> Also, if you plan to attend, please let me know. It is open for all, but it is
>>> nice if we know beforehand who we can expect.
>>>
>>> So if you have a topic that you want to discuss there, then just reply to this
>>> post. If possible, please add a rough idea of how much time you think you will
>>> need.
>>>
>>> I plan to make the agenda based on the received topics around mid-October.
>>>
>>
>> I"m attending and I want to propose a discussion:
>>
>> Topic: V4L2 Explicit Syncronization
>> Purpose: quick overview and discuss of the API/direction we are going
>> with fences
>> Duration: 20-30min
> 
> I would have loved to attend the Media mini-summit. Unfortunately I
> already made plans to leave Friday. In addition participating in the
> V4L2 Explicit Syncronization discussion, it would have been good to
> discuss:
> 
> the my pending Media/Audio resource sharing patch series that is
> dependent on Sakari's lifetime managemnet patch series.

I heard you were trying to extend your stay to include the Friday. Let me
know if you'll be able to attend this summit and I can add this topic to
the list. If you can't join us on Friday, then we can discuss this on the
Thursday: we should have enough time for that.

> I have been unable to get any discussion going on this topic on the
> mailing list.

I suspect that as long as the core life-time issues aren't solved nothing
much will happen with this. It's like building a house on quicksand.

It wasn't obvious that the foundation was quicksand when you started, but
the realization slowly dawned on us that there were more problems than we
thought. Or at least, this is my understanding.

Regards,

	Hans

Re: [ANN] Call for topics for the media mini-summit on Friday Oct 27 in Prague

[Shuah Khan]

Hi Hans,

On 10/13/2017 01:36 AM, Hans Verkuil wrote:
> Hi Shuah,
> 
> On 10/05/2017 03:53 PM, Shuah Khan wrote:
>> Hi Hans/Gustavo.
>>
>> On Wed, Oct 4, 2017 at 1:34 PM, Gustavo Padovan <gustavo@padovan.org> wrote:
>>> Hi Hans,
>>>
>>>
>>>
>>> On Fri, Sep 1, 2017 at 6:46 AM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>>>> Hi all,
>>>>
>>>> We are organizing a media mini-summit on Friday October 27 in Prague, co-located
>>>> with the ELCE conference:
>>>>
>>>> http://events.linuxfoundation.org/events/embedded-linux-conference-europe
>>>>
>>>> This is a call for topics to discuss during that mini-summit.
>>>>
>>>> Also, if you plan to attend, please let me know. It is open for all, but it is
>>>> nice if we know beforehand who we can expect.
>>>>
>>>> So if you have a topic that you want to discuss there, then just reply to this
>>>> post. If possible, please add a rough idea of how much time you think you will
>>>> need.
>>>>
>>>> I plan to make the agenda based on the received topics around mid-October.
>>>>
>>>
>>> I"m attending and I want to propose a discussion:
>>>
>>> Topic: V4L2 Explicit Syncronization
>>> Purpose: quick overview and discuss of the API/direction we are going
>>> with fences
>>> Duration: 20-30min
>>
>> I would have loved to attend the Media mini-summit. Unfortunately I
>> already made plans to leave Friday. In addition participating in the
>> V4L2 Explicit Syncronization discussion, it would have been good to
>> discuss:
>>
>> the my pending Media/Audio resource sharing patch series that is
>> dependent on Sakari's lifetime managemnet patch series.
> 
> I heard you were trying to extend your stay to include the Friday. Let me
> know if you'll be able to attend this summit and I can add this topic to
> the list. If you can't join us on Friday, then we can discuss this on the
> Thursday: we should have enough time for that.

It is turning out to be tough and way too expensive to change travel dates.
Thanks for putting this topic on the agenda for Thursday.

> 
>> I have been unable to get any discussion going on this topic on the
>> mailing list.
> 
> I suspect that as long as the core life-time issues aren't solved nothing
> much will happen with this. It's like building a house on quicksand.

Yes. We have to decide on going forward path to address these life-time
issues.

> 
> It wasn't obvious that the foundation was quicksand when you started, but
> the realization slowly dawned on us that there were more problems than we
> thought. Or at least, this is my understanding.

Right. Not a surprise as we poke around more it became clear that the framework
is fragile.

If I could add one more item for discussion for Thursday if time permits.

Proposing lock contention in mmap and v4l2 ioctl paths

I also have one more item for discussion. I am debugging a deadlock problem
while running gstreamer pipeline involving s5p_mfc and exynos-gsc drivers with
CONFIG_DEBUG_ATOMIC_SLEEP and CONFIG_PROVE_LOCKING are enabled.

Lock contention (race condition) between v4l2_ioctl and drivers fops:mmap interface.

v4l2_ioctl -> video_ioctl2 -> video_usercopy
vm_mmap_pgoff -> v4l2_mmap -> s5p_mfc_mmap

driver mmap routine tries to hold the video device lock it already holds
and in the debug path mm->mmap_sem gets held

I think this might be an issue with m2m drivers that hold the video device
lock from the mmap routines. This could be a manifestation of remove
V4L2_FL_LOCK_ALL_FOPS work at least in the case of s5p_mfc.

It isn't consistent in the way drivers call v4l2_m2m_mmap(). Some drivers
hold a lock and others don't.

I am working on a couple of patches to fix this contention and we could
either discuss this on the mailing list and/or on Thursday.

thanks,
-- Shuah

Re: [ANN] Call for topics for the media mini-summit on Friday Oct 27 in Prague

[Hans Verkuil]

On 10/13/17 16:43, Shuah Khan wrote:
> Hi Hans,
> 
> On 10/13/2017 01:36 AM, Hans Verkuil wrote:
>> Hi Shuah,
>>
>> On 10/05/2017 03:53 PM, Shuah Khan wrote:
>>> Hi Hans/Gustavo.
>>>
>>> On Wed, Oct 4, 2017 at 1:34 PM, Gustavo Padovan <gustavo@padovan.org> wrote:
>>>> Hi Hans,
>>>>
>>>>
>>>>
>>>> On Fri, Sep 1, 2017 at 6:46 AM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>>>>> Hi all,
>>>>>
>>>>> We are organizing a media mini-summit on Friday October 27 in Prague, co-located
>>>>> with the ELCE conference:
>>>>>
>>>>> http://events.linuxfoundation.org/events/embedded-linux-conference-europe
>>>>>
>>>>> This is a call for topics to discuss during that mini-summit.
>>>>>
>>>>> Also, if you plan to attend, please let me know. It is open for all, but it is
>>>>> nice if we know beforehand who we can expect.
>>>>>
>>>>> So if you have a topic that you want to discuss there, then just reply to this
>>>>> post. If possible, please add a rough idea of how much time you think you will
>>>>> need.
>>>>>
>>>>> I plan to make the agenda based on the received topics around mid-October.
>>>>>
>>>>
>>>> I"m attending and I want to propose a discussion:
>>>>
>>>> Topic: V4L2 Explicit Syncronization
>>>> Purpose: quick overview and discuss of the API/direction we are going
>>>> with fences
>>>> Duration: 20-30min
>>>
>>> I would have loved to attend the Media mini-summit. Unfortunately I
>>> already made plans to leave Friday. In addition participating in the
>>> V4L2 Explicit Syncronization discussion, it would have been good to
>>> discuss:
>>>
>>> the my pending Media/Audio resource sharing patch series that is
>>> dependent on Sakari's lifetime managemnet patch series.
>>
>> I heard you were trying to extend your stay to include the Friday. Let me
>> know if you'll be able to attend this summit and I can add this topic to
>> the list. If you can't join us on Friday, then we can discuss this on the
>> Thursday: we should have enough time for that.
> 
> It is turning out to be tough and way too expensive to change travel dates.
> Thanks for putting this topic on the agenda for Thursday.

No problem. I'll post an updated agenda for the Thursday meeting next week.

> 
>>
>>> I have been unable to get any discussion going on this topic on the
>>> mailing list.
>>
>> I suspect that as long as the core life-time issues aren't solved nothing
>> much will happen with this. It's like building a house on quicksand.
> 
> Yes. We have to decide on going forward path to address these life-time
> issues.
> 
>>
>> It wasn't obvious that the foundation was quicksand when you started, but
>> the realization slowly dawned on us that there were more problems than we
>> thought. Or at least, this is my understanding.
> 
> Right. Not a surprise as we poke around more it became clear that the framework
> is fragile.
> 
> If I could add one more item for discussion for Thursday if time permits.
> 
> Proposing lock contention in mmap and v4l2 ioctl paths
> 
> I also have one more item for discussion. I am debugging a deadlock problem
> while running gstreamer pipeline involving s5p_mfc and exynos-gsc drivers with
> CONFIG_DEBUG_ATOMIC_SLEEP and CONFIG_PROVE_LOCKING are enabled.
> 
> Lock contention (race condition) between v4l2_ioctl and drivers fops:mmap interface.
> 
> v4l2_ioctl -> video_ioctl2 -> video_usercopy
> vm_mmap_pgoff -> v4l2_mmap -> s5p_mfc_mmap
> 
> driver mmap routine tries to hold the video device lock it already holds
> and in the debug path mm->mmap_sem gets held
> 
> I think this might be an issue with m2m drivers that hold the video device
> lock from the mmap routines. This could be a manifestation of remove
> V4L2_FL_LOCK_ALL_FOPS work at least in the case of s5p_mfc.
> 
> It isn't consistent in the way drivers call v4l2_m2m_mmap(). Some drivers
> hold a lock and others don't.
> 
> I am working on a couple of patches to fix this contention and we could
> either discuss this on the mailing list and/or on Thursday.

The mmap driver function shouldn't take a lock. The vb2_mmap function has its
own lock that it uses to protect the critical section.

I wasn't aware that there were still vb2-using drivers that took a lock in
their mmap function.

This used to be a major problem in the past, but since the mmap_lock was added
to vb2_queue this hasn't been an issue.

I think this is just old code (the s5p drivers are old!) that was never updated.
I'm not sure this is something we need to discuss, IMHO it is just a bug.

See also the (long!) commit log for f035eb4e976ef5a059e30bc91cfd310ff030a7d3
where this lock was added for all the gory details.

Regards,

	Hans

Re: [ANN] Call for topics for the media mini-summit on Friday Oct 27 in Prague

[Shuah Khan]

On 10/13/2017 09:05 AM, Hans Verkuil wrote:
> On 10/13/17 16:43, Shuah Khan wrote:
>> Hi Hans,
>>
>> On 10/13/2017 01:36 AM, Hans Verkuil wrote:
>>> Hi Shuah,
>>>
>>> On 10/05/2017 03:53 PM, Shuah Khan wrote:
>>>> Hi Hans/Gustavo.
>>>>
>>>> On Wed, Oct 4, 2017 at 1:34 PM, Gustavo Padovan <gustavo@padovan.org> wrote:
>>>>> Hi Hans,
>>>>>
>>>>>
>>>>>
>>>>> On Fri, Sep 1, 2017 at 6:46 AM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>>>>>> Hi all,
>>>>>>
>>>>>> We are organizing a media mini-summit on Friday October 27 in Prague, co-located
>>>>>> with the ELCE conference:
>>>>>>
>>>>>> http://events.linuxfoundation.org/events/embedded-linux-conference-europe
>>>>>>
>>>>>> This is a call for topics to discuss during that mini-summit.
>>>>>>
>>>>>> Also, if you plan to attend, please let me know. It is open for all, but it is
>>>>>> nice if we know beforehand who we can expect.
>>>>>>
>>>>>> So if you have a topic that you want to discuss there, then just reply to this
>>>>>> post. If possible, please add a rough idea of how much time you think you will
>>>>>> need.
>>>>>>
>>>>>> I plan to make the agenda based on the received topics around mid-October.
>>>>>>
>>>>>
>>>>> I"m attending and I want to propose a discussion:
>>>>>
>>>>> Topic: V4L2 Explicit Syncronization
>>>>> Purpose: quick overview and discuss of the API/direction we are going
>>>>> with fences
>>>>> Duration: 20-30min
>>>>
>>>> I would have loved to attend the Media mini-summit. Unfortunately I
>>>> already made plans to leave Friday. In addition participating in the
>>>> V4L2 Explicit Syncronization discussion, it would have been good to
>>>> discuss:
>>>>
>>>> the my pending Media/Audio resource sharing patch series that is
>>>> dependent on Sakari's lifetime managemnet patch series.
>>>
>>> I heard you were trying to extend your stay to include the Friday. Let me
>>> know if you'll be able to attend this summit and I can add this topic to
>>> the list. If you can't join us on Friday, then we can discuss this on the
>>> Thursday: we should have enough time for that.
>>
>> It is turning out to be tough and way too expensive to change travel dates.
>> Thanks for putting this topic on the agenda for Thursday.
> 
> No problem. I'll post an updated agenda for the Thursday meeting next week.
> 
>>
>>>
>>>> I have been unable to get any discussion going on this topic on the
>>>> mailing list.
>>>
>>> I suspect that as long as the core life-time issues aren't solved nothing
>>> much will happen with this. It's like building a house on quicksand.
>>
>> Yes. We have to decide on going forward path to address these life-time
>> issues.
>>
>>>
>>> It wasn't obvious that the foundation was quicksand when you started, but
>>> the realization slowly dawned on us that there were more problems than we
>>> thought. Or at least, this is my understanding.
>>
>> Right. Not a surprise as we poke around more it became clear that the framework
>> is fragile.
>>
>> If I could add one more item for discussion for Thursday if time permits.
>>
>> Proposing lock contention in mmap and v4l2 ioctl paths
>>
>> I also have one more item for discussion. I am debugging a deadlock problem
>> while running gstreamer pipeline involving s5p_mfc and exynos-gsc drivers with
>> CONFIG_DEBUG_ATOMIC_SLEEP and CONFIG_PROVE_LOCKING are enabled.
>>
>> Lock contention (race condition) between v4l2_ioctl and drivers fops:mmap interface.
>>
>> v4l2_ioctl -> video_ioctl2 -> video_usercopy
>> vm_mmap_pgoff -> v4l2_mmap -> s5p_mfc_mmap
>>
>> driver mmap routine tries to hold the video device lock it already holds
>> and in the debug path mm->mmap_sem gets held
>>
>> I think this might be an issue with m2m drivers that hold the video device
>> lock from the mmap routines. This could be a manifestation of remove
>> V4L2_FL_LOCK_ALL_FOPS work at least in the case of s5p_mfc.
>>
>> It isn't consistent in the way drivers call v4l2_m2m_mmap(). Some drivers
>> hold a lock and others don't.
>>
>> I am working on a couple of patches to fix this contention and we could
>> either discuss this on the mailing list and/or on Thursday.
> 
> The mmap driver function shouldn't take a lock. The vb2_mmap function has its
> own lock that it uses to protect the critical section.

Right. I noticed that is the case. My patch for exynos-gsc does exactly that.
Thanks for confirming.

> 
> I wasn't aware that there were still vb2-using drivers that took a lock in
> their mmap function.
> 
> This used to be a major problem in the past, but since the mmap_lock was added
> to vb2_queue this hasn't been an issue.
> 
> I think this is just old code (the s5p drivers are old!) that was never updated.
> I'm not sure this is something we need to discuss, IMHO it is just a bug.

Great. I will send the patches I am testing now.

> 
> See also the (long!) commit log for f035eb4e976ef5a059e30bc91cfd310ff030a7d3
> where this lock was added for all the gory details.
> 

Thanks for the pointer.

-- Shuah