linux-kernel - [PATCH v2 4/6] drm/v3d: Drop the wait for L2T flush to complete.

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Message-Id: <20181203222438.25417-4-eric@anholt.net>
Date:   Mon,  3 Dec 2018 14:24:36 -0800
From:   Eric Anholt <eric@...olt.net>
To:     dri-devel@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org,
        Dave Emett <david.emett@...adcom.com>,
        Thomas Spurden <thomas.spurden@...adcom.com>,
        Eric Anholt <eric@...olt.net>
Subject: [PATCH v2 4/6] drm/v3d: Drop the wait for L2T flush to complete.

According to Dave, once you've started an L2T flush, all L2T accesses
will be blocked until the flush completes.  This fixes a consistent
3-4ms stall between the ioctl and running the job, and 3DMMES Taiji
goes from 27fps to 110fps.

v2: Leave a note about why we don't need to wait for completion.

Signed-off-by: Eric Anholt <eric@...olt.net>
Fixes: 57692c94dcbe ("drm/v3d: Introduce a new DRM driver for Broadcom V3D V3.x+")
Reviewed-by: Dave Emett <david.emett@...adcom.com> (v1, comment requested)
---
 drivers/gpu/drm/v3d/v3d_gem.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c
index 01e879c71cad..c268c7c79566 100644
--- a/drivers/gpu/drm/v3d/v3d_gem.c
+++ b/drivers/gpu/drm/v3d/v3d_gem.c
@@ -143,13 +143,13 @@ v3d_invalidate_l2(struct v3d_dev *v3d, int core)
 static void
 v3d_flush_l2t(struct v3d_dev *v3d, int core)
 {
+	/* While there is a busy bit (V3D_L2TCACTL_L2TFLS), we don't
+	 * need to wait for completion before dispatching the job --
+	 * L2T accesses will be stalled until the flush has completed.
+	 */
 	V3D_CORE_WRITE(core, V3D_CTL_L2TCACTL,
 		       V3D_L2TCACTL_L2TFLS |
 		       V3D_SET_FIELD(V3D_L2TCACTL_FLM_FLUSH, V3D_L2TCACTL_FLM));
-	if (wait_for(!(V3D_CORE_READ(core, V3D_CTL_L2TCACTL) &
-		       V3D_L2TCACTL_L2TFLS), 100)) {
-		DRM_ERROR("Timeout waiting for L2T flush\n");
-	}
 }
 
 /* Invalidates the slice caches.  These are read-only caches. */
-- 
2.20.0.rc1