drm/i915: Plumb 'dsb' all way to the plane hooks

We need to be able to do both MMIO and DSB based pipe/plane
programming. To that end plumb the 'dsb' all way from the top
into the plane commit hooks.

The compiler appears smart enough to combine the branches from
all the back-to-back register writes into a single branch.
So the generated asm ends up looking more or less like this:
plane_hook()
{
	if (dsb) {
		intel_dsb_reg_write();
		intel_dsb_reg_write();
		...
	} else {
		intel_de_write_fw();
		intel_de_write_fw();
		...
	}
}
which seems like a reasonably efficient way to do this.

An alternative I was also considering is some kind of closure
(register write function + display vs. dsb pointer passed to it).
That does result is smaller code as there are no branches anymore,
but having each register access go via function pointer sounds
less efficient.

Not that I actually measured the overhead of either approach yet.
Also the reg_rw tracepoint seems to be making a huge mess of the
generated code for the mmio path. And additionally there's some
kind of IS_GSI_REG() hack in __raw_uncore_read() which ends up
generating a pointless branch for every mmio register access.
So looks like there might be quite a bit of room for improvement
in the mmio path still.

Reviewed-by: Animesh Manna <animesh.manna@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240930170415.23841-12-ville.syrjala@linux.intel.com

1 files changed, 13 insertions, 6 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_atomic_plane.h b/drivers/gpu/drm/i915/display/intel_atomic_plane.h
index 6c4fe3596465..0f982f452ff3 100644
--- a/drivers/gpu/drm/i915/display/intel_atomic_plane.h
+++ b/drivers/gpu/drm/i915/display/intel_atomic_plane.h
@@ -14,6 +14,7 @@ struct drm_rect;
 struct intel_atomic_state;
 struct intel_crtc;
 struct intel_crtc_state;
+struct intel_dsb;
 struct intel_plane;
 struct intel_plane_state;
 enum plane_id;
@@ -32,26 +33,32 @@ void intel_plane_copy_uapi_to_hw_state(struct intel_plane_state *plane_state,
 				       struct intel_crtc *crtc);
 void intel_plane_copy_hw_state(struct intel_plane_state *plane_state,
 			       const struct intel_plane_state *from_plane_state);
-void intel_plane_async_flip(struct intel_plane *plane,
+void intel_plane_async_flip(struct intel_dsb *dsb,
+			    struct intel_plane *plane,
 			    const struct intel_crtc_state *crtc_state,
 			    const struct intel_plane_state *plane_state,
 			    bool async_flip);
-void intel_plane_update_noarm(struct intel_plane *plane,
+void intel_plane_update_noarm(struct intel_dsb *dsb,
+			      struct intel_plane *plane,
 			      const struct intel_crtc_state *crtc_state,
 			      const struct intel_plane_state *plane_state);
-void intel_plane_update_arm(struct intel_plane *plane,
+void intel_plane_update_arm(struct intel_dsb *dsb,
+			    struct intel_plane *plane,
 			    const struct intel_crtc_state *crtc_state,
 			    const struct intel_plane_state *plane_state);
-void intel_plane_disable_arm(struct intel_plane *plane,
+void intel_plane_disable_arm(struct intel_dsb *dsb,
+			     struct intel_plane *plane,
 			     const struct intel_crtc_state *crtc_state);
 struct intel_plane *intel_plane_alloc(void);
 void intel_plane_free(struct intel_plane *plane);
 struct drm_plane_state *intel_plane_duplicate_state(struct drm_plane *plane);
 void intel_plane_destroy_state(struct drm_plane *plane,
 			       struct drm_plane_state *state);
-void intel_crtc_planes_update_noarm(struct intel_atomic_state *state,
+void intel_crtc_planes_update_noarm(struct intel_dsb *dsb,
+				    struct intel_atomic_state *state,
 				    struct intel_crtc *crtc);
-void intel_crtc_planes_update_arm(struct intel_atomic_state *state,
+void intel_crtc_planes_update_arm(struct intel_dsb *dsbx,
+				  struct intel_atomic_state *state,
 				  struct intel_crtc *crtc);
 int intel_plane_atomic_check_with_state(const struct intel_crtc_state *old_crtc_state,
 					struct intel_crtc_state *crtc_state,