[RFC PATCH] drm: Add new DIRTY fb flags to pass interlaced alternate fields

[Daniel Vetter]

On Mon, Sep 10, 2018 at 03:02:16PM +0300, Ville Syrjälä wrote:
> On Fri, Sep 07, 2018 at 02:46:21PM -0700, Satish Kumar Nagireddy wrote:
> > The requirement is to render interlaced alternate buffers. In case of
> > alternate, top field and bottom field are in two different buffers.
> > 
> > The question is, can we pass existing flags DRM_MODE_PRESENT_TOP_FIELD
> > and DRM_MODE_PRESENT_TOP_FIELD to DRM_IOCTL_MODE_SETPLANE ioctl?
> 
> The original idea with those flags was bob deinterlacing type of stuff.
> 
> For fbs with non-interleaved fields I think we'd have to extend addfb
> somewhat to allow passing a separate buffer for each field. The problem
> with that is that we only have 4 buffers in addfb, so we'd run out for
> three plane formats. So we'd have to increase the number of buffers in
> addfb, or add some kind of implicit assumption on how the fields are
> stored in the single bo (which I presume might not even be possible on
> some crazy hardware).

Yeah given that an fb is supposed to stick around potentially forever, I
think we need to have both fields in one logical framebuffer object. But I
have no idea how exactly we'd best go about for this, at least for true
interlaced. Doubling up the drm_mode_fb_cmd2 structure (including fourcc
and modifiers, or not?) is probably simplest.
-Daniel

> > But in case if urrent frame out of display range, application
> > will invoke DRM_IOCTL_MODE_PAGE_FLIP ioctl. So, it is not guaranteed
> > that application will always call setplane(), it may also call page_flip().
> > Then we will have to introduce two more flags to pass with page_flip()
> > ioctl, which is complicating things.
> > 
> > Background of DRM_IOCTL_MODE_DIRTYFB ioctl: This ioctl is defined, so
> > that userspace can notify the driver that an area of framebuffer has
> > changed and should be flushed to display hardware.
> > 
> > The proposed solution is to introduce new dirty fb flags, so that userspace
> > can pass them with every alternate field buffer and the same is reached
> > display hardware. This patch adds new dirty framebuffer flags, so that
> > application can pass interlaced alternate field information to driver.
> > 
> > Signed-off-by: Satish Kumar Nagireddy <satish.nagireddy.nagireddy at xilinx.com>
> > ---
> >  include/uapi/drm/drm_mode.h | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> > index ce7efe2..40fef85 100644
> > --- a/include/uapi/drm/drm_mode.h
> > +++ b/include/uapi/drm/drm_mode.h
> > @@ -428,7 +428,9 @@ struct drm_mode_fb_cmd2 {
> >  
> >  #define DRM_MODE_FB_DIRTY_ANNOTATE_COPY 0x01
> >  #define DRM_MODE_FB_DIRTY_ANNOTATE_FILL 0x02
> > -#define DRM_MODE_FB_DIRTY_FLAGS         0x03
> > +#define DRM_MODE_FB_DIRTY_TOP_FIELD     0x03
> > +#define DRM_MODE_FB_DIRTY_BOTTOM_FIELD  0x04
> > +#define DRM_MODE_FB_DIRTY_FLAGS         0x07
> >  
> >  #define DRM_MODE_FB_DIRTY_MAX_CLIPS     256
> >  
> > -- 
> > 2.7.4
> > 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> -- 
> Ville Syrjälä
> Intel
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> dri-devel at lists.freedesktop.org
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch