linux-kernel - [PATCH 11/18] drm/bridge: cdns-dsi: Remove broken fifo emptying check

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Message-Id: <20250320-cdns-dsi-impro-v1-11-725277c5f43b@ideasonboard.com>
Date: Thu, 20 Mar 2025 18:00:06 +0200
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>
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>, 
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Subject: [PATCH 11/18] drm/bridge: cdns-dsi: Remove broken fifo emptying
 check

The driver check 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.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
---
 drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 28 --------------------------
 1 file changed, 28 deletions(-)

diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
index 9797e6faa29d..e85c8652c96e 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
@@ -453,15 +453,6 @@ bridge_to_cdns_dsi_input(struct drm_bridge *bridge)
 	return container_of(bridge, struct cdns_dsi_input, bridge);
 }
 
-static unsigned int mode_to_dpi_hfp(const struct drm_display_mode *mode,
-				    bool mode_valid_check)
-{
-	if (mode_valid_check)
-		return mode->hsync_start - mode->hdisplay;
-
-	return mode->crtc_hsync_start - mode->crtc_hdisplay;
-}
-
 static unsigned int dpi_to_dsi_timing(unsigned int dpi_timing,
 				      unsigned int dpi_bpp,
 				      unsigned int dsi_pkt_overhead)
@@ -583,7 +574,6 @@ 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 mode_clock = (mode_valid_check ? mode->clock : mode->crtc_clock);
 	unsigned long req_hs_clk_rate;
@@ -617,24 +607,6 @@ static int cdns_dsi_check_conf(struct cdns_dsi *dsi,
 		return -EINVAL;
 	}
 
-	if (output->dev->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE) {
-		dsi_hss_hsa_hse_hbp = dsi_cfg->hbp + DSI_HBP_FRAME_PULSE_OVERHEAD;
-		dsi_hss_hsa_hse_hbp += dsi_cfg->hsa + DSI_HSA_FRAME_OVERHEAD;
-	} else {
-		dsi_hss_hsa_hse_hbp = dsi_cfg->hbp + DSI_HBP_FRAME_EVENT_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_to_dpi_hfp(mode, mode_valid_check) * nlanes <
-	    (u64)dsi_hss_hsa_hse_hbp *
-	    (mode_valid_check ? mode->clock : mode->crtc_clock) * 1000)
-		return -EINVAL;
-
 	return 0;
 }
 

-- 
2.43.0