linux-kernel - [PATCH v3 1/2] drm/rockchip: vop: clear DMA stop bit upon vblank on RK3066

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Date: Mon, 27 May 2024 20:11:49 -0300
From: Val Packett <val@...kett.cool>
To: Heiko Stübner <heiko@...ech.de>
Cc: Val Packett <val@...kett.cool>,
	stable@...r.kernel.org,
	Sandy Huang <hjc@...k-chips.com>,
	Andy Yan <andy.yan@...k-chips.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	dri-devel@...ts.freedesktop.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3 1/2] drm/rockchip: vop: clear DMA stop bit upon vblank on RK3066

The RK3066 VOP sets a dma_stop bit when it's done scanning out a frame
and needs the driver to acknowledge that by clearing the bit.

So unless we clear it "between" frames, the RGB output only shows noise
instead of the picture. vblank seems to be the most appropriate place to
do it, since it indicates exactly that: that the hardware is done
with the frame.

This seems to be a redundant synchronization mechanism that was removed
in later iterations of the VOP hardware block.

Fixes: f4a6de8 ("drm: rockchip: vop: add rk3066 vop definitions")
Cc: stable@...r.kernel.org
Signed-off-by: Val Packett <val@...kett.cool>
---
 drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 6 ++++++
 drivers/gpu/drm/rockchip/rockchip_drm_vop.h | 1 +
 drivers/gpu/drm/rockchip/rockchip_vop_reg.c | 1 +
 3 files changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
index a13473b2d..2731fe2b2 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
@@ -1766,6 +1766,12 @@ static void vop_handle_vblank(struct vop *vop)
 	}
 	spin_unlock(&drm->event_lock);
 
+	if (VOP_HAS_REG(vop, common, dma_stop)) {
+		spin_lock(&vop->reg_lock);
+		VOP_REG_SET(vop, common, dma_stop, 0);
+		spin_unlock(&vop->reg_lock);
+	}
+
 	if (test_and_clear_bit(VOP_PENDING_FB_UNREF, &vop->pending))
 		drm_flip_work_commit(&vop->fb_unref_work, system_unbound_wq);
 }
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.h b/drivers/gpu/drm/rockchip/rockchip_drm_vop.h
index b33e5bdc2..0cf512cc1 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.h
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.h
@@ -122,6 +122,7 @@ struct vop_common {
 	struct vop_reg lut_buffer_index;
 	struct vop_reg gate_en;
 	struct vop_reg mmu_en;
+	struct vop_reg dma_stop;
 	struct vop_reg out_mode;
 	struct vop_reg standby;
 };
diff --git a/drivers/gpu/drm/rockchip/rockchip_vop_reg.c b/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
index b9ee02061..9bcb40a64 100644
--- a/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
+++ b/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
@@ -466,6 +466,7 @@ static const struct vop_output rk3066_output = {
 };
 
 static const struct vop_common rk3066_common = {
+	.dma_stop = VOP_REG(RK3066_SYS_CTRL0, 0x1, 0),
 	.standby = VOP_REG(RK3066_SYS_CTRL0, 0x1, 1),
 	.out_mode = VOP_REG(RK3066_DSP_CTRL0, 0xf, 0),
 	.cfg_done = VOP_REG(RK3066_REG_CFG_DONE, 0x1, 0),
-- 
2.45.1