On 10/21/19 11:48 AM, Tomasz Figa wrote:
> On Mon, Oct 21, 2019 at 6:38 PM Hans Verkuil <hverk...@xs4all.nl> wrote:
>> On 10/21/19 11:26 AM, Tomasz Figa wrote:
>>> On Mon, Oct 21, 2019 at 5:41 PM Hans Verkuil <hverk...@xs4all.nl> wrote:
>>>> On 10/8/19 11:11 AM, Boris Brezillon wrote:
>>>>> This is part of the multiplanar and singleplanar unification process.
>>>>> v4l2_ext_pix_format is supposed to work for both cases.
>>>>> We also add the concept of modifiers already employed in DRM to expose
>>>>> HW-specific formats (like tiled or compressed formats) and allow
>>>>> exchanging this information with the DRM subsystem in a consistent way.
>>>>> Note that V4L2_BUF_TYPE_VIDEO[_OUTPUT]_OVERLAY and
>>>>> V4L2_BUF_TYPE_VIDEO_{CAPTURE,OUTPUT}_MPLANE types are no longer accepted
>>>>> in v4l2_ext_format and will be rejected if you use the {G,S,TRY}EXT_FMT
>>>>> ioctls. V4L2_BUF_TYPE_VIDEO_{CAPTURE,OUTPUT}_MPLANE is dropped as part
>>>>> of the multiplanar/singleplanar unification.
>>>>> V4L2_BUF_TYPE_VIDEO[_OUTPUT]_OVERLAY seems to be used mostly on old
>>>>> drivers and supporting it would require some extra rework.
>>>>> New hooks have been added to v4l2_ioctl_ops to support those new ioctls
>>>>> in drivers, but, in the meantime, the core takes care of converting
>>>>> {S,G,TRY}_EXT_FMT requests into {S,G,TRY}_FMT so that old drivers can
>>>>> still work if the userspace app/lib uses the new ioctls.
>>>>> The conversion is also done the other around to allow userspace
>>>>> apps/libs using {S,G,TRY}_FMT to work with drivers implementing the
>>>>> _ext_ hooks.
>>>>> Signed-off-by: Boris Brezillon <boris.brezil...@collabora.com>
>>>>> ---
>>>> <snip>
>>>>> +#define VIDIOC_G_EXT_FMT     _IOWR('V', 104, struct v4l2_ext_format)
>>>>> +#define VIDIOC_S_EXT_FMT     _IOWR('V', 105, struct v4l2_ext_format)
>>>>> +#define VIDIOC_TRY_EXT_FMT   _IOWR('V', 106, struct v4l2_ext_format)
>>>>>  /* Reminder: when adding new ioctls please add support for them to
>>>>>     drivers/media/v4l2-core/v4l2-compat-ioctl32.c as well! */
>>>> Since we're extending g/s/try_fmt, we should also provide a replacement for
>>>> enum_fmt, esp. given this thread:
>>>> https://www.mail-archive.com/linux-media@vger.kernel.org/msg150871.html
>>> While that's a completely valid problem that should be addressed, I'm
>>> not sure if putting all the things in one bag would have a positive
>>> effect on solving all the problems in a reasonable timeline.
>> I'm not sure what you mean with this. We can't ignore this either, and if
>> we're going to add these new ioctls, then let's try to fix as much as we can.
> My point is that this series solves a completely orthogonal problem
> without a need to touch ENUM_FMT at all. Is there any reason why
> solving this particular problem separately would make solving the
> ENUM_FMT problem more difficult in the future?

I do not agree with you that this is an orthogonal problem. If we are creating
new FMT ioctls to solve various problems, then it makes sense to look at ALL the
problems, including this. We might decide to postpone creating a EXT_ENUM_FMT
ioctl, but during the discussion we should look at this issue as well.

To take one suggestion you made: use of the active/try slots for existing non-MC
drivers. If we decide to go into that direction (and I think it is a very 
idea), then that requires that ENUM_FMT is taken into account anyway. And 
other ioctls such as the selection API as well.

I think we need to think big here, and try to at least explore the possibility
of creating an API that tries to limit the differences between video and subdev

>>>> So here is a preliminary suggestion:
>>>> struct v4l2_ext_fmtdesc {
>>>>         __u32               index;             /* Format number      */
>>>>         __u32               type;              /* enum v4l2_buf_type */
>>>>         __u32               which;             /* enum 
>>>> v4l2_subdev_format_whence, ignored if mbus_code == 0 */
>>>>         __u32               mbus_code;         /* Mediabus Code (set to 0 
>>>> if n/a) */
>>>>         __u32               flags;
>>>>         __u8                description[32];   /* Description string */
>>>>         __u32               pixelformat;       /* Format fourcc      */
>>>> };
>>>> This would solve (I think) the issue raised in the thread since you can 
>>>> now get
>>>> just for formats that are valid for the given mediabus code and the which 
>>>> field.
>>> Hmm, why only mbus_code? We have the same problem with mem2mem
>>> devices, where the format set on one queue affects the formats
>>> supported on another queue. Perhaps it should be defined to return
>>> formats valid with the current state of the driver? If we want to
>>> extend it to return formats for arbitrary states, perhaps we should
>>> use a mechanism similar to the TRY_FMT slot in subdevices, where we
>>> can set the configuration we want to test against and then ENUM_FMT
>>> would return the formats valid for that configuration?
>> Good point.
> We might want to keep the control'ification of the API in mind, which
> should simplify dealing with state inter-dependencies, because all the
> state would be represented in a uniform way.

I still don't know what Laurent wants to do with that.

>>>> Other improvements that could be made is to return more information about 
>>>> the
>>>> format (similar to struct v4l2_format_info). In particular 
>>>> v4l2_pixel_encoding
>>>> and mem/comp_planes would be useful for userspace to know.
>>> An alternative would be to go away from mixing mem_planes and
>>> pixelformats and just having the "planarity" queryable and
>>> configurable separately. The existing duplicated FourCCs would have to
>>> remain for compatibility reasons, though.
>> Interesting idea, but I don't know if this would make the API more or less 
>> confusing.
> Yeah, this definitely needs more thought. My experience with working
> with many people trying to use V4L2 in the userspace tells me that the
> existing model is confusing, though. DRM and most userspace libraries
> use FourCCs only to define the pixelformats themselves and planarity
> is a separate aspect.
> The target model that I'd see happening would be to have the
> multiple-memory plane semantics used everywhere, so all color planes
> are described as separate entities, up to having different DMA-buf
> FDs. Then the single memory plane case would be just one of the
> specific cases, where all the DMA-buf FDs point to the same buffer and
> color plane offsets are laid out contiguously, which could be enforced
> by generic code when queuing the buffer if that's a hardware
> requirement.

Do you think you can come up with a rough proposal before the ELCE session?



>>>> Finally, we can also add a new ioctl that combines 
>>>> and returns an array of all valid formats/sizes/intervals, requiring just 
>>>> a single ioctl
>>>> to obtain all this information.
>>> While it definitely sounds like a useful thing to have, it would be an
>>> interesting problem to solve given the inter-dependencies between
>>> pads, queues and other state, as in the mbus example above.
>> This is definitely a separate issue for further in the future.
> Agreed.
> Best regards,
> Tomasz

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