linux-kernel - [PATCH v4 08/17] drm/bridge: cdns-dsi: Remove broken fifo emptying check

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Message-Id: <20250618-cdns-dsi-impro-v4-8-862c841dbe02@ideasonboard.com>
Date: Wed, 18 Jun 2025 12:59:11 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Jyri Sarha <jyri.sarha@....fi>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>, 
 Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Jayesh Choudhary <j-choudhary@...com>, Dmitry Baryshkov <lumag@...nel.org>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 linux-phy@...ts.infradead.org, Francesco Dolcini <francesco@...cini.it>, 
 Aradhya Bhatia <aradhya.bhatia@...ux.dev>, 
 Devarsh Thakkar <devarsht@...com>, 
 Parth Pancholi <parth.pancholi@...adex.com>, 
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Subject: [PATCH v4 08/17] drm/bridge: cdns-dsi: Remove broken fifo emptying
 check

The driver checks if "DPI(HFP) > DSI(HSS+HSA+HSE+HBP)", and rejects the
mode if not.

However, testing shows that this doesn't hold at all. I can set the hfp
to very small values, with no errors. The feedback from the HW team also
was that the check is not right, although it's not clear if there's a
way to validate the FIFO emptying.

The check rejects quite a lot of modes, apparently for no good reason,
so drop the check.

Tested-by: Parth Pancholi <parth.pancholi@...adex.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
---
 drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 15 ---------------
 1 file changed, 15 deletions(-)

diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
index eae9469ef431..000c5a2367fe 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
@@ -553,7 +553,6 @@ static int cdns_dsi_check_conf(struct cdns_dsi *dsi,
 {
 	struct cdns_dsi_output *output = &dsi->output;
 	struct phy_configure_opts_mipi_dphy *phy_cfg = &output->phy_opts.mipi_dphy;
-	unsigned long dsi_hss_hsa_hse_hbp;
 	unsigned int nlanes = output->dev->lanes;
 	int ret;
 
@@ -575,20 +574,6 @@ static int cdns_dsi_check_conf(struct cdns_dsi *dsi,
 	if (ret)
 		return ret;
 
-	dsi_hss_hsa_hse_hbp = dsi_cfg->hbp + DSI_HBP_FRAME_OVERHEAD;
-	if (output->dev->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE)
-		dsi_hss_hsa_hse_hbp += dsi_cfg->hsa + DSI_HSA_FRAME_OVERHEAD;
-
-	/*
-	 * Make sure DPI(HFP) > DSI(HSS+HSA+HSE+HBP) to guarantee that the FIFO
-	 * is empty before we start a receiving a new line on the DPI
-	 * interface.
-	 */
-	if ((u64)phy_cfg->hs_clk_rate *
-	    (mode->hsync_start - mode->hdisplay) * nlanes <
-	    (u64)dsi_hss_hsa_hse_hbp * mode->clock  * 1000)
-		return -EINVAL;
-
 	return 0;
 }
 

-- 
2.43.0