On Mon, 2017-06-19 at 12:10 +0200, Hans Verkuil wrote: > On 06/19/2017 12:03 PM, Minghsiu Tsai wrote: > > Hi, Hans, > > > > On Fri, 2017-06-16 at 12:42 +0200, Hans Verkuil wrote: > >> On 05/12/17 04:42, Minghsiu Tsai wrote: > >>> From: Daniel Kurtz <djkurtz@xxxxxxxxxxxx> > >>> > >>> Experiments show that the: > >>> (1) mtk-mdp uses the _MPLANE form of CAPTURE/OUTPUT > >> > >> Please drop this, since this no longer applies to this patch. > >> > > > > I will remove it next version > > > > > >>> (2) CAPTURE types use CROP targets, and OUTPUT types use COMPOSE targets > >> > >> Are you really certain about this? > >> > >> For m2m devices the output (i.e. memory to hardware) typically crops from memory > >> and the capture side (hardware to memory) composes into memory. > >> > >> I.e.: for the output side you crop the part of the memory buffer that you want > >> to process and on the capture side you compose the result into a memory buffer: > >> i.e. the memory buffer might be 1920x1080, but you compose the decoder output > >> into a rectangle of 640x480 at offset 128x128 within that buffer (just an example). > >> > >> CAPTURE using crop would be if, before the data is DMAed, the hardware decoder > >> output is cropped. E.g. if the stream fed to the decoder is 1920x1080, but you > >> want to only DMA a subselection of that, then that would be cropping, and it > >> would go to a memory buffer of the size of the crop selection. > >> > >> OUTPUT using compose is highly unlikely: that means that the frame you give > >> is composed in a larger internal buffer with generated border data around it. > >> Very rare and really only something that a compositor of some sort would do. > >> > > > > That's strange. In v4l2-ioctl.c, v4l_g_crop() > > OUTPUT is using COMPOSE > > CAPTURE is using CROP > > The old crop API can't be used with most (all?) codec drivers. Codec drivers do > exactly the opposite of what the old crop API did. > > It is the reason the selection API was created. > > The old crop API was written for SDTV receivers where the hardware would crop > the received video. For output (rarely used) the hardware would compose the > image into a larger (PAL or NTSC sizes) frame. > > Applications have to use the selection API to work with codec drivers. Just > ignore the old crop ioctls, they are not suitable for such hardware. > Hi, Hans, Thanks for your review and comment. Conclusion is application uses wrong ioctls, g/s_crop. > > > > static int v4l_g_crop(const struct v4l2_ioctl_ops *ops, > > struct file *file, void *fh, void *arg) > > ... > > /* crop means compose for output devices */ > > if (V4L2_TYPE_IS_OUTPUT(p->type)) > > s.target = V4L2_SEL_TGT_COMPOSE_ACTIVE; > > else > > s.target = V4L2_SEL_TGT_CROP_ACTIVE; > > > > ret = ops->vidioc_g_selection(file, fh, &s); > > > > > >> What exactly does the hardware do? Both for the encoder and for the decoder > >> case. Perhaps if I knew exactly what that is, then I can advise. > >> > > > > NV12M/YUV420M/MT21 -> MDP -> NV12M/YUV420M > > > > The usage would be like this: > > For decoder: > > decoder -> MT21 -> MDP -> NV12M/YUV420M > > > > For encoder: > > NV12M/YUV420M -> MDP -> NV12M/YUV420M -> encoder > > That doesn't help. Where in these two chains does the cropping (encoder) or > composing (decoder) take place? I assume it is the DMA engine that read from > a rectangle in the source buffer (encoder) or writes to a rectangle in the > destination buffer (decoder). > Yes. they are only buffer transfer between decoder, mdp and encoder. > And in that case the current driver is correct. Next step, we will try to refine framework in userspace code. > I wonder if the g/s_crop description in the V4L2 Specification should get a > big fat warning that it doesn't apply to codec drivers and that the selection > API should be used instead. A patch for that is welcome! > > Regards, > > Hans
