[PATCH] drm/i915/display: Send DSI DCS commands with pipeline flush in High Speed

[gareth.yu at intel.com]

From: Gareth Yu <gareth.yu at intel.com>

With all of the boundary conditions when streaming the commands B2B in our
validation (part of the reason we added the flush),  the Flush effectively
serializes the transmission of each command enqueued within the command
dispatcher to one per V. Blank line which simplifies the behavior of the
High Speed Arbitration.

So, unless we absolutely have to burst these to the Sink, we should be using
the Pipeline Flush bit to serialize the commands.

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14247

Cc : Suraj Kandpal <suraj.kandpal at intel.com>
Cc : Jani Nikula <jani.nikula at intel.com>
Signed-off-by: Gareth Yu <gareth.yu at intel.com>
---
 drivers/gpu/drm/i915/display/icl_dsi.c      | 4 ++--
 drivers/gpu/drm/i915/display/icl_dsi_regs.h | 1 +
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/icl_dsi.c b/drivers/gpu/drm/i915/display/icl_dsi.c
index 402b7b2e1829..f91f27067768 100644
--- a/drivers/gpu/drm/i915/display/icl_dsi.c
+++ b/drivers/gpu/drm/i915/display/icl_dsi.c
@@ -191,12 +191,12 @@ static int dsi_send_pkt_hdr(struct intel_dsi_host *host,
 	else
 		tmp &= ~PAYLOAD_PRESENT;
 
-	tmp &= ~VBLANK_FENCE;
+	tmp &= ~(VBLANK_FENCE | LP_DATA_TRANSFER | PIPELINE_FLUSH);
 
 	if (enable_lpdt)
 		tmp |= LP_DATA_TRANSFER;
 	else
-		tmp &= ~LP_DATA_TRANSFER;
+		tmp |= PIPELINE_FLUSH;
 
 	tmp &= ~(PARAM_WC_MASK | VC_MASK | DT_MASK);
 	tmp |= ((packet->header[0] & VC_MASK) << VC_SHIFT);
diff --git a/drivers/gpu/drm/i915/display/icl_dsi_regs.h b/drivers/gpu/drm/i915/display/icl_dsi_regs.h
index d4845ac65acc..b601b7632339 100644
--- a/drivers/gpu/drm/i915/display/icl_dsi_regs.h
+++ b/drivers/gpu/drm/i915/display/icl_dsi_regs.h
@@ -272,6 +272,7 @@
 #define  PAYLOAD_PRESENT		(1 << 31)
 #define  LP_DATA_TRANSFER		(1 << 30)
 #define  VBLANK_FENCE			(1 << 29)
+#define  PIPELINE_FLUSH			(1 << 28)
 #define  PARAM_WC_MASK			(0xffff << 8)
 #define  PARAM_WC_LOWER_SHIFT		8
 #define  PARAM_WC_UPPER_SHIFT		16
-- 
2.34.1