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SubjectRe: [PATCH v2] [media] mtk-mdp: Fix g_/s_selection capture/compose logic
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 <>
> >
> > 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()

static int v4l_g_crop(const struct v4l2_ioctl_ops *ops,
struct file *file, void *fh, void *arg)
/* crop means compose for output devices */

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

> Regards,
> Hans

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