[RFC] drm: Introduce max width and height properties for planes
Daniel Vetter
daniel at ffwll.ch
Wed May 25 13:12:45 UTC 2016
On Wed, May 25, 2016 at 04:28:36PM +0530, Archit Taneja wrote:
> On 05/25/2016 12:40 PM, Daniel Vetter wrote:
> >- Is the size/width really independent of e.g. rotation/pixel format/...
> > Should it be the maximum that's possible under best circumstance (things
> > could still fail), or the minimum that's guaranteed to work everwhere.
> > This is the kind of stuff we need the userspace part for, too.
>
> Yeah, it isn't independent of these parameters. I'm not entirely sure
> about this either.
>
> Does it make sense to impose a rule that the user first sets the
> rotation/format plane properties, and only then read the maximum
> width? I'm assuming user space hates such kind of stuff.
>
> If we use the 'best circumstance' max_width, we can first start
> with a minimum number of planes that need to be grouped to achieve
> the target mode. If that fails the atomic test, then we can try to
> add one plane at a time, and reduce the width for each plane.
>
> If we use the minimum/'guaranteed to work' max_width, we'll get
> a higher number of planes than needed for this mode. This would pass
> the atomic test. We could then reduce a plane at a time and see when
> we fail the atomic test.
>
> I guess we need to chose the one that's more probable to get right
> the first time. Considering only pixel formats for now, the
> minimum/'guaranteed to work' would map to the RGB formats. The best
> circumstance ones would probably be the planar video formats. Since
> we use RGB more often, the minimum one might make more sense.
>
> We could, of course, give the property a range of max widths to
> confuse user space even more.
An entirely different idea for cases where a simple hint property doesn't
work (other ideas floating around are can_scale, to give a hint whether a
plan can at least in theory up/downscale, or not at all), is that the
kernel gives more specific hints about what it would like to change.
So if userspace asks for a plane, but for the given pixel format it's too
wide, the kernel could return a new proposed value for width. That would
be super-flexible and could cover all kinds of use-case like rotation
needing a specific tiling (fb_modifier) or specific pixel format, or
specific stride.
For the case at hand there's even more worms: What about stride
requirements? Afaik on some hw you just need to split the buffers into 2
planes, but can keep the wide stride (since the limit is the size of the
linebuffers in the hw). On others you need to split the buffer itself into
2, because the plane hw can't cope with huge strides. Again might depend
upon the pixel format.
So in a way height/width is both too much information and not precise
enough. Entirely different approches:
- We just add a might_need_split_plane prop to crtcs where this might be
needed. Userspace then gets to retry with split buffers if it doesn't
work with a huge one.
- When I discussed this with qualcom folks for msm we concluded that the
simplest approach would be to hide this in the kernel. So if you have a
too wide plane, and need 2 hw planes to scan it out, then do that
transparently in the kernel. Of course this means that there will be 1
(or 3 if you need a 2x2 split) fewer planes available, but userspace
needs to iteratively build up the plane config using ATOMIC_TEST anyway.
If possible for your hw I'm heavily leaning towards this last approach. If
fits entirely into the current atomic design, and all the complexity is
restricted to your driver (you need to have some allocation map between
drm planes and real hw planes, but that's it).
Thoughts?
-Daniel
>
> Archit
>
> >
> >Cheers, Daniel
> >
> >>Signed-off-by: Archit Taneja <architt at codeaurora.org>
> >>---
> >> drivers/gpu/drm/drm_atomic.c | 9 +++++++++
> >> drivers/gpu/drm/drm_crtc.c | 38 ++++++++++++++++++++++++++++++++++++++
> >> include/drm/drm_crtc.h | 6 ++++++
> >> 3 files changed, 53 insertions(+)
> >>
> >>diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> >>index 8ee1db8..fded22a 100644
> >>--- a/drivers/gpu/drm/drm_atomic.c
> >>+++ b/drivers/gpu/drm/drm_atomic.c
> >>@@ -839,6 +839,15 @@ static int drm_atomic_plane_check(struct drm_plane *plane,
> >> return -ERANGE;
> >> }
> >>
> >>+ if (plane->max_width && (state->src_w >> 16) > plane->max_width ||
> >>+ plane->max_height && (state->src_h >> 16) > plane->max_height) {
> >>+ DRM_DEBUG_ATOMIC("Invalid source width/height "
> >>+ "%u.%06ux%u.%06u\n",
> >>+ state->src_w >> 16, ((state->src_w & 0xffff) * 15625) >> 10,
> >>+ state->src_h >> 16, ((state->src_h & 0xffff) * 15625) >> 10);
> >>+ return -ERANGE;
> >>+ }
> >>+
> >> fb_width = state->fb->width << 16;
> >> fb_height = state->fb->height << 16;
> >>
> >>diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> >>index e08f962..f2d3b92 100644
> >>--- a/drivers/gpu/drm/drm_crtc.c
> >>+++ b/drivers/gpu/drm/drm_crtc.c
> >>@@ -1267,6 +1267,9 @@ int drm_universal_plane_init(struct drm_device *dev, struct drm_plane *plane,
> >> plane->possible_crtcs = possible_crtcs;
> >> plane->type = type;
> >>
> >>+ plane->max_width = 0;
> >>+ plane->max_height = 0;
> >>+
> >> list_add_tail(&plane->head, &config->plane_list);
> >> config->num_total_plane++;
> >> if (plane->type == DRM_PLANE_TYPE_OVERLAY)
> >>@@ -4957,6 +4960,41 @@ int drm_mode_plane_set_obj_prop(struct drm_plane *plane,
> >> }
> >> EXPORT_SYMBOL(drm_mode_plane_set_obj_prop);
> >>
> >>+int drm_plane_create_max_width_prop(struct drm_plane *plane, uint32_t max_width)
> >>+{
> >>+ struct drm_property *prop;
> >>+
> >>+ prop = drm_property_create_range(plane->dev, DRM_MODE_PROP_IMMUTABLE,
> >>+ "MAX_W", max_width, max_width);
> >>+ if (!prop)
> >>+ return -ENOMEM;
> >>+
> >>+ drm_object_attach_property(&plane->base, prop, max_width);
> >>+
> >>+ plane->max_width = max_width;
> >>+
> >>+ return 0;
> >>+}
> >>+EXPORT_SYMBOL(drm_plane_create_max_width_prop);
> >>+
> >>+int drm_plane_create_max_height_prop(struct drm_plane *plane,
> >>+ uint32_t max_height)
> >>+{
> >>+ struct drm_property *prop;
> >>+
> >>+ prop = drm_property_create_range(plane->dev, DRM_MODE_PROP_IMMUTABLE,
> >>+ "MAX_H", max_height, max_height);
> >>+ if (!prop)
> >>+ return -ENOMEM;
> >>+
> >>+ drm_object_attach_property(&plane->base, prop, max_height);
> >>+
> >>+ plane->max_height = max_height;
> >>+
> >>+ return 0;
> >>+}
> >>+EXPORT_SYMBOL(drm_plane_create_max_height_prop);
> >>+
> >> /**
> >> * drm_mode_obj_get_properties_ioctl - get the current value of a object's property
> >> * @dev: DRM device
> >>diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> >>index e0170bf..6104527 100644
> >>--- a/include/drm/drm_crtc.h
> >>+++ b/include/drm/drm_crtc.h
> >>@@ -1531,6 +1531,8 @@ struct drm_plane {
> >> uint32_t *format_types;
> >> unsigned int format_count;
> >> bool format_default;
> >>+ uint32_t max_width;
> >>+ uint32_t max_height;
> >>
> >> struct drm_crtc *crtc;
> >> struct drm_framebuffer *fb;
> >>@@ -2550,6 +2552,10 @@ extern struct drm_property *drm_mode_create_rotation_property(struct drm_device
> >> unsigned int supported_rotations);
> >> extern unsigned int drm_rotation_simplify(unsigned int rotation,
> >> unsigned int supported_rotations);
> >>+extern int drm_plane_create_max_width_prop(struct drm_plane *plane,
> >>+ uint32_t max_width);
> >>+extern int drm_plane_create_max_height_prop(struct drm_plane *plane,
> >>+ uint32_t max_height);
> >>
> >> /* Helpers */
> >>
> >>--
> >>The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> >>hosted by The Linux Foundation
> >>
> >
>
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> hosted by The Linux Foundation
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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