Re: [PATCH v4 6/6] drm/i915: Add skl_check_nv12_surface for NV12

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Apr 19, 2018 at 02:36:42AM +0000, Srinivas, Vidya wrote:
> 
> 
> 
> 
> > -----Original Message-----
> 
> > From: Ville Syrjälä [mailto:ville.syrjala@linux.intel.com]
> 
> > Sent: Thursday, April 19, 2018 12:06 AM
> 
> > To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> 
> > Cc: Srinivas, Vidya <vidya.srinivas@intel.com>; intel-
> 
> > gfx@lists.freedesktop.org
> 
> > Subject: Re: [Intel-gfx] [PATCH v4 6/6] drm/i915: Add
> 
> > skl_check_nv12_surface for NV12
> 
> >
> 
> > On Wed, Apr 18, 2018 at 08:06:57PM +0200, Maarten Lankhorst wrote:
> 
> > > Op 18-04-18 om 17:32 schreef Ville Syrjälä:
> 
> > > > On Wed, Apr 18, 2018 at 09:38:13AM +0530, Vidya Srinivas wrote:
> 
> > > >> From: Maarten Lankhorst <maarten.lankhorst@linux.intel.com<mailto:maarten.lankhorst@linux.intel.com>>
> 
> > > >>
> 
> > > >> We skip src trunction/adjustments for
> 
> > > >> NV12 case and handle the sizes directly.
> 
> > > >> Without this, pipe fifo underruns are seen on APL/KBL.
> 
> > > >>
> 
> > > >> v2: For NV12, making the src coordinates multiplier of 4
> 
> > > >>
> 
> > > >> v3: Moving all the src coords handling code for NV12 to
> 
> > > >> skl_check_nv12_surface
> 
> > > >>
> 
> > > >> Signed-off-by: Maarten Lankhorst
> 
> > > >> <maarten.lankhorst@linux.intel.com<mailto:maarten.lankhorst@linux.intel.com>>
> 
> > > >> Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com<mailto:vidya.srinivas@intel.com>>
> 
> > > >> ---
> 
> > > >>  drivers/gpu/drm/i915/intel_display.c | 39
> 
> > > >> ++++++++++++++++++++++++++++++++++++
> 
> > > >>  drivers/gpu/drm/i915/intel_sprite.c  | 15 ++++++++++----
> 
> > > >>  2 files changed, 50 insertions(+), 4 deletions(-)
> 
> > > >>
> 
> > > >> diff --git a/drivers/gpu/drm/i915/intel_display.c
> 
> > > >> b/drivers/gpu/drm/i915/intel_display.c
> 
> > > >> index 925402e..b8dbaca 100644
> 
> > > >> --- a/drivers/gpu/drm/i915/intel_display.c
> 
> > > >> +++ b/drivers/gpu/drm/i915/intel_display.c
> 
> > > >> @@ -3118,6 +3118,42 @@ static int skl_check_main_surface(const
> 
> > struct intel_crtc_state *crtc_state,
> 
> > > >>  return 0;
> 
> > > >>  }
> 
> > > >>
> 
> > > >> +static int
> 
> > > >> +skl_check_nv12_surface(const struct intel_crtc_state *crtc_state,
> 
> > > >> +                                       struct intel_plane_state *plane_state) {
> 
> > > >> +                int crtc_x2 = plane_state->base.crtc_x + plane_state->base.crtc_w;
> 
> > > >> +                int crtc_y2 = plane_state->base.crtc_y +
> 
> > > >> +plane_state->base.crtc_h;
> 
> > > >> +
> 
> > > >> +                if (((plane_state->base.src_x >> 16) % 4) != 0 ||
> 
> > > >> +                    ((plane_state->base.src_y >> 16) % 4) != 0 ||
> 
> > > >> +                    ((plane_state->base.src_w >> 16) % 4) != 0 ||
> 
> > > >> +                    ((plane_state->base.src_h >> 16) % 4) != 0) {
> 
> > > >> +                                DRM_DEBUG_KMS("src coords must be multiple of 4 for
> 
> > NV12\n");
> 
> > > >> +                                return -EINVAL;
> 
> > > >> +                }
> 
> > > > I don't really see why we should check these. The clipped
> 
> > > > coordinates are what matters.
> 
> > >
> 
> > > To propagate our limits to the userspace. I think we should do it for
> 
> > > all formats, but NV12 is the first YUV format we have tests for. If we
> 
> > > could we should do something similar for the other YUV formats, but they
> 
> > have different requirements.
> 
> > >
> 
> > > In case of NV12 we don't have existing userspace, there will be
> 
> > > nothing that breaks if we enforce limits from the start.
> 
> >
> 
> > But what about sub-pixel coordinates? You're totally ignoring them here.
> 
> > We need to come up with some proper rules for this stuff.
> 
> >
> 
> > >
> 
> > > >> +
> 
> > > >> +                /* Clipping would cause a 1-3 pixel gap at the edge of the screen? */
> 
> > > >> +                if ((crtc_x2 > crtc_state->pipe_src_w && crtc_state->pipe_src_w %
> 
> > 4) ||
> 
> > > >> +                    (crtc_y2 > crtc_state->pipe_src_h && crtc_state->pipe_src_h % 4))
> 
> > {
> 
> > > >> +                                DRM_DEBUG_KMS("It's not possible to clip %u,%u to
> 
> > %u,%u\n",
> 
> > > >> +                                                      crtc_x2, crtc_y2,
> 
> > > >> +                                                      crtc_state->pipe_src_w, crtc_state->pipe_src_h);
> 
> > > >> +                                return -EINVAL;
> 
> > > >> +                }
> 
> > > > Why should we care? The current code already plays it fast and loose
> 
> > > > and allows the dst rectangle to shrink to accomodate the hw limits.
> 
> > > > If we want to change that we should change it universally.
> 
> > >
> 
> > > Unfortunately for the other formats we already have an existing
> 
> > > userspace
> 
> > > (X.org) that doesn't perform any validation. We can't change it for
> 
> > > that, but we can prevent future mistakes.
> 
> >
> 
> > We should do it uniformly. Not per-format. That will make the code
> 
> > unmaintainable real quick.
> 
> >
> 
> > >
> 
> > > >> +
> 
> > > >> +                plane_state->base.src.x1 =
> 
> > > >> +                                DIV_ROUND_CLOSEST(plane_state->base.src.x1, 1 << 18) <<
> 
> > 18;
> 
> > > >> +                plane_state->base.src.x2 =
> 
> > > >> +                                DIV_ROUND_CLOSEST(plane_state->base.src.x2, 1 << 18) <<
> 
> > 18;
> 
> > > >> +                plane_state->base.src.y1 =
> 
> > > >> +                                DIV_ROUND_CLOSEST(plane_state->base.src.y1, 1 << 18) <<
> 
> > 18;
> 
> > > >> +                plane_state->base.src.y2 =
> 
> > > >> +                                DIV_ROUND_CLOSEST(plane_state->base.src.y2, 1 << 18) <<
> 
> > 18;
> 
> > > > Since this can now increase the size of the source rectangle our
> 
> > > > scaling factor checks are no longer 100% valid. We might end up with
> 
> > > > a scaling factor that is too high.
> 
> > > >
> 
> > > > I don't really like any of these "let's make NV12 behave special"
> 
> > > > tricks. We should make the code behave the same way for all pixel
> 
> > > > formats instead of adding format specific hacks.
> 
> > >
> 
> > > This is not nivalid because we restrict the original src coordinates
> 
> > > to be a multiple of 4, you can only clip to something smaller, not to
> 
> > > something bigger. :)
> 
> >
> 
> > The clipped coordinates can be whatever thanks to scaling/etc.
> 
> >
> 
> > Also why are we trying to make everything a multiple of four? I don't
> 
> > remember any hw restrictions like that.
> 
> 
> 
> Hi
> 
> 
> As per WA1106, Display corruption/color shift observed when using NV12 with 270 rotation or 90 rotation + horizontal flip.
> 
> WA: NV12 with 270 rotation or 90 rotation + horizontal flip requires the programmed plane height to be a multiple of 4.

Does plane height here mean src height or dst height?

Either way I don't see why we aren't just checking for the right thing
instead of trying to mandate a four pixel alignment everywhere.

> 
> 
> 
> As per experiments on APL and KBL, when we don't keep them multiple of 4, we see fifo underruns.
> 
> 
> 
> Regards
> 
> Vidya
> 
> 
> 
> >
> 
> > --
> 
> > Ville Syrjälä
> 
> > Intel

-- 
Ville Syrjälä
Intel
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