On 11/04/2013 12:29 PM, Sylwester Nawrocki wrote:
> Sorry, I missed to reply to this e-mail.
>
> On 04/11/13 11:57, Hans Verkuil wrote:
>> Hi John,
>>
>> On 10/18/2013 02:03 AM, John Sheu wrote:
>>> On Thu, Oct 17, 2013 at 3:54 PM, Sylwester Nawrocki
>>> <sylvester.nawro...@gmail.com> wrote:
>>>> On 10/18/2013 12:25 AM, John Sheu wrote:
>>>>> On Thu, Oct 17, 2013 at 2:46 PM, John Sheu<s...@google.com> wrote:
>>>>>>> Sweet. Thanks for spelling things out explicitly like this. The fact
>>>>>>> that the CAPTURE and OUTPUT queues "invert" their sense of "crop-ness"
>>>>>>> when used in a m2m device is definitely all sorts of confusing.
>>>>>
>>>>> Just to double-check: this means that we have another bug.
>>>>>
>>>>> In drivers/media/v4l2-core/v4l2-ioctl.c, in v4l_s_crop and v4l_g_crop,
>>>>> we "simulate" a G_CROP or S_CROP, if the entry point is not defined
>>>>> for that device, by doing the appropriate S_SELECTION or G_SELECTION.
>>>>> Unfortunately then, for M2M this is incorrect then.
>>>>>
>>>>> Am I reading this right?
>>>>
>>>> You are right, John. Firstly a clear specification needs to be written,
>>>> something along the lines of Tomasz's explanation in this thread, once
>>>> all agree to that the ioctl code should be corrected if needed.
>>
>> I don't understand the problem here. The specification has always been clear:
>> s_crop for output devices equals s_selection(V4L2_SEL_TGT_COMPOSE_ACTIVE).
>>
>> Drivers should only implement the selection API and the v4l2 core will do the
>> correct translation of s_crop.
>>
>> Yes, I know it's weird, but that's the way the crop API was defined way back
>> and that's what should be used.
>>
>> My advise: forget about s_crop and just implement s_selection.
>>
>>>>
>>>> It seems this [1] RFC is an answer exactly to your question.
>>>>
>>>> Exact meaning of the selection ioctl is only part of the problem, also
>>>> interaction with VIDIOC_S_FMT is not currently defined in the V4L2 spec.
>>>>
>>>> [1] http://www.spinics.net/lists/linux-media/msg56078.html
>>>
>>> I think the "inversion" behavior is confusing and we should remove it
>>> if at all possible.
>>>
>>> I took a look through all the drivers in linux-media which implement
>>> S_CROP. Most of them are either OUTPUT or CAPTURE/OVERLAY-only. Of
>>> those that aren't:
>>>
>>> * drivers/media/pci/zoran/zoran_driver.c : this driver explicitly accepts
>>> both
>>> OUTPUT and CAPTURE queues in S_CROP, but they both configure the same
>>> state.
>>> No functional difference.
>>
>> Yeah, I guess that's a driver bug. This is a very old driver that originally
>> used a custom API for these things, and since no selection API existed at the
>> time it was just mapped to the crop API. Eventually it should use the
>> selection
>> API as well and do it correctly. But to be honest, nobody cares about this
>> driver :-)
>>
>> It is however on my TODO list of drivers that need to be converted to the
>> latest
>> frameworks, so I might fix this eventually.
>>
>>> * drivers/media/platform/davinci/vpfe_capture.c : this driver doesn't
>>> specify
>>> the queue, but is a CAPTURE-only device. Probably an (unrelated) bug.
>>
>> Yes, that's a driver bug. It should check the buffer type.
>>
>>> * drivers/media/platform/exynos4-is/fimc-m2m.c : this driver is a m2m driver
>>> with both OUTPUT and CAPTURE queues. It has uninverted behavior:
>>> S_CROP(CAPTURE) -> source
>>> S_CROP(OUTPUT) -> destination
>
> No, that's not true. It seems you got it wrong, cropping in case of this m2m
> driver works like this:
>
> S_CROP(OUTPUT) -> source (from HW POV)
> S_CROP(CAPTURE) -> destination
>
> I.e. exactly same way as for s5p-g2d, for which it somehow was a reference
> implementation.
>
>> This is the wrong behavior.
>>
>>> * drivers/media/platform/s5p-g2d/g2d.c : this driver is a m2m driver with
>>> both
>>> OUTPUT and CAPTURE queues. It has inverted behavior:
>>> S_CROP(CAPTURE) -> destination
>>> S_CROP(OUTPUT) -> source
>>
>> This is the correct behavior.
>>
>>>
>>> The last two points above are the most relevant. So we already have
>>> at least one broken driver, regardless of whether we allow inversion
>>> or not; I'd think this grants us a certain freedom to redefine the
>>> specification to be more logical. Can we do this please?
>>
>> No. The fimc-m2m.c driver needs to be fixed. That's the broken one.
>
> It's not broken, it's easy to figure out if you actually look at the
> code, e.g. fimc_m2m_try_crop() function.
I did look at the code, but it is quite possible I got confused.
Let me be precise as to what should happen, and you can check whether that's
what is actually done in the fimc and g2d drivers.
For V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE:
Say that the mem2mem hardware creates a 640x480 picture. If VIDIOC_S_CROP was
called for V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE with a rectangle of
320x240@160x120,
then the DMA engine will only transfer the center 320x240 rectangle to memory.
This means that S_FMT needs to provide a buffer size large enough to accomodate
a 320x240 image.
So: VIDIOC_S_CROP(CAPTURE) == S_SELECTION(CAPTURE, V4L2_SEL_TGT_CROP).
For V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE:
Say that the image in memory is a 640x480 picture. If VIDIOC_S_CROP was called
for V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE with a rectangle of 320x240@160x120 then
this would mean that the full 640x480 image is DMAed to the hardware, is scaled
down to 320x240 and composed at position (160x120) in a canvas of at least
480x360.
In other words, S_CROP behaves as composition for output devices:
VIDIOC_S_CROP(OUTPUT) == S_SELECTION(OUTPUT, V4L2_SEL_TGT_COMPOSE).
The last operation in particular is almost certainly not what you want for
m2m devices. Instead, you want to select (crop) part of the image in memory and
DMA that to the device. This is S_SELECTION(OUTPUT, V4L2_SEL_TGT_CROP) and
cannot
be translated to an S_CROP ioctl.
What's more: in order to implement S_SELECTION(OUTPUT, V4L2_SEL_TGT_COMPOSE) you
would need some way of setting the 'canvas' size of the m2m device, and there is
no API today to do this (this was discussed during the v4l/dvb mini-summit).
Regarding the capture side of an m2m device: it is not clear to me what these
drivers implement: S_SELECTION(CAPTURE, V4L2_SEL_TGT_CROP) or
S_SELECTION(CAPTURE, V4L2_SEL_TGT_COMPOSE).
If it is the latter, then again S_CROP cannot be used and you have to use
S_SELECTION.
Regards,
Hans
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