linux-kernel - [PATCH 24/29] drm/tidss: dispc: Improve mode checking logs

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Message-Id: <20250902-drm-state-readout-v1-24-14ad5315da3f@kernel.org>
Date: Tue, 02 Sep 2025 10:32:52 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
 Simona Vetter <simona@...ll.ch>, 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>, 
 Jyri Sarha <jyri.sarha@....fi>, 
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Devarsh Thakkar <devarsht@...com>, dri-devel@...ts.freedesktop.org, 
 linux-kernel@...r.kernel.org, Maxime Ripard <mripard@...nel.org>
Subject: [PATCH 24/29] drm/tidss: dispc: Improve mode checking logs

The dispc_vp_mode_valid() function checks whether a mode can be handled
by the display controller.

There's a whole bunch of criteria, and it's not clear when a rejection
happens why it did. Let's add a bunch of logs on error to make it
clearer.

Signed-off-by: Maxime Ripard <mripard@...nel.org>
---
 drivers/gpu/drm/tidss/tidss_dispc.c | 47 +++++++++++++++++++++++++++++--------
 1 file changed, 37 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c b/drivers/gpu/drm/tidss/tidss_dispc.c
index 32248b5f71b7566dc33d7a7db0efb26d3a9ed1c3..ef948e3041e10bc65cf2c4794a4e4cffa7e3fb3a 100644
--- a/drivers/gpu/drm/tidss/tidss_dispc.c
+++ b/drivers/gpu/drm/tidss/tidss_dispc.c
@@ -1349,47 +1349,63 @@ static void dispc_vp_set_default_color(struct dispc_device *dispc,
 
 enum drm_mode_status dispc_vp_mode_valid(struct dispc_device *dispc,
 					 u32 hw_videoport,
 					 const struct drm_display_mode *mode)
 {
+	struct tidss_device *tidss = dispc->tidss;
+	struct drm_device *dev = &tidss->ddev;
 	u32 hsw, hfp, hbp, vsw, vfp, vbp;
 	enum dispc_vp_bus_type bus_type;
 	int max_pclk;
 
 	bus_type = dispc->feat->vp_bus_type[hw_videoport];
 
 	max_pclk = dispc->feat->max_pclk_khz[bus_type];
 
-	if (WARN_ON(max_pclk == 0))
+	if (WARN_ON(max_pclk == 0)) {
+		drm_dbg(dev, "Invalid maximum pixel clock");
 		return MODE_BAD;
+	}
 
-	if (mode->clock < dispc->feat->min_pclk_khz)
+	if (mode->clock < dispc->feat->min_pclk_khz) {
+		drm_dbg(dev, "Mode pixel clock below hardware minimum pixel clock");
 		return MODE_CLOCK_LOW;
+	}
 
-	if (mode->clock > max_pclk)
+	if (mode->clock > max_pclk) {
+		drm_dbg(dev, "Mode pixel clock above hardware maximum pixel clock");
 		return MODE_CLOCK_HIGH;
+	}
 
-	if (mode->hdisplay > 4096)
+	if (mode->hdisplay > 4096) {
+		drm_dbg(dev, "Number of active horizontal pixels above hardware limits.");
 		return MODE_BAD;
+	}
 
-	if (mode->vdisplay > 4096)
+	if (mode->vdisplay > 4096) {
+		drm_dbg(dev, "Number of active vertical lines above hardware limits.");
 		return MODE_BAD;
+	}
 
 	/* TODO: add interlace support */
-	if (mode->flags & DRM_MODE_FLAG_INTERLACE)
+	if (mode->flags & DRM_MODE_FLAG_INTERLACE) {
+		drm_dbg(dev, "Interlace modes not suppported.");
 		return MODE_NO_INTERLACE;
+	}
 
 	/*
 	 * Enforce the output width is divisible by 2. Actually this
 	 * is only needed in following cases:
 	 * - YUV output selected (BT656, BT1120)
 	 * - Dithering enabled
 	 * - TDM with TDMCycleFormat == 3
 	 * But for simplicity we enforce that always.
 	 */
-	if ((mode->hdisplay % 2) != 0)
+	if ((mode->hdisplay % 2) != 0) {
+		drm_dbg(dev, "Number of active horizontal pixels must be even.");
 		return MODE_BAD_HVALUE;
+	}
 
 	hfp = mode->hsync_start - mode->hdisplay;
 	hsw = mode->hsync_end - mode->hsync_start;
 	hbp = mode->htotal - mode->hsync_end;
 
@@ -1397,29 +1413,40 @@ enum drm_mode_status dispc_vp_mode_valid(struct dispc_device *dispc,
 	vsw = mode->vsync_end - mode->vsync_start;
 	vbp = mode->vtotal - mode->vsync_end;
 
 	if (hsw < 1 || hsw > 256 ||
 	    hfp < 1 || hfp > 4096 ||
-	    hbp < 1 || hbp > 4096)
+	    hbp < 1 || hbp > 4096) {
+		drm_dbg(dev,
+			"Horizontal blanking or sync outside of hardware limits (fp: %u, sw: %u, bp: %u).",
+			hfp, hsw, hbp);
 		return MODE_BAD_HVALUE;
+	}
 
 	if (vsw < 1 || vsw > 256 ||
-	    vfp > 4095 || vbp > 4095)
+	    vfp > 4095 || vbp > 4095) {
+		drm_dbg(dev,
+			"Vertical blanking or sync outside of hardware limits (fp: %u, sw: %u, bp: %u).",
+			vfp, vsw, vbp);
 		return MODE_BAD_VVALUE;
+	}
 
 	if (dispc->memory_bandwidth_limit) {
 		const unsigned int bpp = 4;
 		u64 bandwidth;
 
 		bandwidth = 1000 * mode->clock;
 		bandwidth = bandwidth * mode->hdisplay * mode->vdisplay * bpp;
 		bandwidth = div_u64(bandwidth, mode->htotal * mode->vtotal);
 
-		if (dispc->memory_bandwidth_limit < bandwidth)
+		if (dispc->memory_bandwidth_limit < bandwidth) {
+			drm_dbg(dev, "Required memory bandwidth outside of hardware limits.");
 			return MODE_BAD;
+		}
 	}
 
+	drm_dbg(dev, "Mode is valid.");
 	return MODE_OK;
 }
 
 int dispc_vp_enable_clk(struct dispc_device *dispc, u32 hw_videoport)
 {

-- 
2.50.1