Re: [PATCH 08/12] drm/i915: Add NV12 support to intel_framebuffer_init

From: Daniel Vetter <daniel@ffwll.ch>
To: "Konduru, Chandra" <chandra.konduru@intel.com>
Cc: "Vetter, Daniel" <daniel.vetter@intel.com>,
	"intel-gfx@lists.freedesktop.org"
	<intel-gfx@lists.freedesktop.org>,
	arthur.j.runyan@intel.com, "Syrjala,
	Ville" <ville.syrjala@intel.com>
Subject: Re: [PATCH 08/12] drm/i915: Add NV12 support to intel_framebuffer_init
Date: Thu, 21 May 2015 11:33:42 +0200	[thread overview]
Message-ID: <20150521093342.GQ15256@phenom.ffwll.local> (raw)
In-Reply-To: <76A9B330A4D78C4D99CB292C4CC06C0E36FE8564@fmsmsx101.amr.corp.intel.com>

On Thu, May 21, 2015 at 12:31:49AM +0000, Konduru, Chandra wrote:
> 
> 
> > -----Original Message-----
> > From: Daniel Vetter [mailto:daniel.vetter@ffwll.ch] On Behalf Of Daniel Vetter
> > Sent: Wednesday, May 20, 2015 12:37 AM
> > To: Konduru, Chandra
> > Cc: Daniel Vetter; intel-gfx@lists.freedesktop.org; Vetter, Daniel; Syrjala, Ville
> > Subject: Re: [Intel-gfx] [PATCH 08/12] drm/i915: Add NV12 support to
> > intel_framebuffer_init
> > 
> > On Tue, May 19, 2015 at 04:31:54PM +0000, Konduru, Chandra wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Daniel Vetter [mailto:daniel.vetter@ffwll.ch] On Behalf Of Daniel
> > Vetter
> > > > Sent: Tuesday, May 19, 2015 1:24 AM
> > > > To: Konduru, Chandra
> > > > Cc: intel-gfx@lists.freedesktop.org; Vetter, Daniel; Syrjala, Ville
> > > > Subject: Re: [Intel-gfx] [PATCH 08/12] drm/i915: Add NV12 support to
> > > > intel_framebuffer_init
> > > >
> > > > On Sun, May 17, 2015 at 10:11:01PM -0700, Chandra Konduru wrote:
> > > > > This patch adds NV12 as supported format to
> > > > > intel_framebuffer_init and performs various checks.
> > > > >
> > > > > Signed-off-by: Chandra Konduru <chandra.konduru@intel.com>
> > > > > Testcase: igt/kms_nv12
> > > > > ---
> > > > >  drivers/gpu/drm/i915/intel_display.c |   27
> > +++++++++++++++++++++++++++
> > > > >  1 file changed, 27 insertions(+)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/i915/intel_display.c
> > > > b/drivers/gpu/drm/i915/intel_display.c
> > > > > index 42924a6..41cd26f 100644
> > > > > --- a/drivers/gpu/drm/i915/intel_display.c
> > > > > +++ b/drivers/gpu/drm/i915/intel_display.c
> > > > > @@ -14043,6 +14043,33 @@ static int intel_framebuffer_init(struct
> > > > drm_device *dev,
> > > > >  			return -EINVAL;
> > > > >  		}
> > > > >  		break;
> > > > > +	case DRM_FORMAT_NV12:
> > > > > +		if (INTEL_INFO(dev)->gen < 9) {
> > > > > +			DRM_DEBUG("unsupported pixel format: %s\n",
> > > > > +				  drm_get_format_name(mode_cmd-
> > > > >pixel_format));
> > > > > +			return -EINVAL;
> > > > > +		}
> > > > > +		if (!mode_cmd->offsets[1]) {
> > > > > +			DRM_DEBUG("uv start offset not set\n");
> > > > > +			return -EINVAL;
> > > > > +		}
> > > >
> > > > Nope. It's perfectly ok to have NV12 with a 0 offset for the uv plane, if
> > > > it's e.g. in a separate buffer object. Which is the part this series seems
> > > > to be completely missing - there's no code at all to look up (and store in
> > > > intel_framebuffer the 2nd i915_bo pointer) the 2nd buffer handle afaics.
> > > >
> > > > You should also change your igts to use 2 separate buffers, just for test
> > > > coverage.
> > > > -Daniel
> > >
> > > Hi Daniel,
> > > Agree, in general that is very well ok. But as skl hw requires uv to be after
> > > y in gtt. This can be guaranteed by having a single bo and y and uv offsets
> > > into it. Above sanity checks in i915 specific fb init call are for that reason.
> > > There are definitely ways to guarantee uv to be after y even with two
> > > separate bos (by uv remapping), but I see that is unnecessary
> > > complication and not sure value by allowing that. Or am I missing
> > > something here?
> > 
> > For a start you don't reject multiplane stuff where this isn't the case.
> > And if we indeed have the hw requirement that the gtt address for y must
> > be before the gtt address for uv (sounds strange to me, definitely need a
> > bspec reference for that) then we need to check that throughroughly:
> > Currently you could place Y after UV even in a single BO.
> 
> Hi Daniel,
> NV12 programming is documented in bspec under display planes 
> "Plane Planar YUV programming". There it talks about aux_dist
> which is the distance between y and uv planes expecting uv to be
> after y.

Bspec talks about wrap-around, which at least indicates that this might be
possible and the hw doesn't have a real restriction here. Art, can you
please double-check whether we could wrape-around PLANE_AUX_DIST with a
2s complement to avoid placement restrictions on the aux buffers?

Bspec doesn't say anything about this being required to be positive ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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