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, 14 insertions, 8 deletions

diff --git a/drivers/gpu/drm/i915/display/i9xx_plane.c b/drivers/gpu/drm/i915/display/i9xx_plane.c
index 9447f7229b60..17a1e3801a85 100644
--- a/drivers/gpu/drm/i915/display/i9xx_plane.c
+++ b/drivers/gpu/drm/i915/display/i9xx_plane.c
@@ -416,7 +416,8 @@ static int i9xx_plane_min_cdclk(const struct intel_crtc_state *crtc_state,
 	return DIV_ROUND_UP(pixel_rate * num, den);
 }
 
-static void i9xx_plane_update_noarm(struct intel_plane *plane,
+static void i9xx_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)
 {
@@ -444,7 +445,8 @@ static void i9xx_plane_update_noarm(struct intel_plane *plane,
 	}
 }
 
-static void i9xx_plane_update_arm(struct intel_plane *plane,
+static void i9xx_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)
 {
@@ -507,7 +509,8 @@ static void i9xx_plane_update_arm(struct intel_plane *plane,
 				  intel_plane_ggtt_offset(plane_state) + dspaddr_offset);
 }
 
-static void i830_plane_update_arm(struct intel_plane *plane,
+static void i830_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)
 {
@@ -517,11 +520,12 @@ static void i830_plane_update_arm(struct intel_plane *plane,
 	 * Additional breakage on i830 causes register reads to return
 	 * the last latched value instead of the last written value [ALM026].
 	 */
-	i9xx_plane_update_noarm(plane, crtc_state, plane_state);
-	i9xx_plane_update_arm(plane, crtc_state, plane_state);
+	i9xx_plane_update_noarm(dsb, plane, crtc_state, plane_state);
+	i9xx_plane_update_arm(dsb, plane, crtc_state, plane_state);
 }
 
-static void i9xx_plane_disable_arm(struct intel_plane *plane,
+static void i9xx_plane_disable_arm(struct intel_dsb *dsb,
+				   struct intel_plane *plane,
 				   const struct intel_crtc_state *crtc_state)
 {
 	struct drm_i915_private *dev_priv = to_i915(plane->base.dev);
@@ -549,7 +553,8 @@ static void i9xx_plane_disable_arm(struct intel_plane *plane,
 }
 
 static void
-g4x_primary_async_flip(struct intel_plane *plane,
+g4x_primary_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)
@@ -569,7 +574,8 @@ g4x_primary_async_flip(struct intel_plane *plane,
 }
 
 static void
-vlv_primary_async_flip(struct intel_plane *plane,
+vlv_primary_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)