[PATCH v2 25/28] drm/tidss: dispc: Improve mode checking logs

[Maxime Ripard <mripard@kernel.org>]

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. Add logs on each rejection criterion to make it
clearer.

Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
 drivers/gpu/drm/tidss/tidss_dispc.c | 45 +++++++++++++++++++++++++++++--------
 1 file changed, 36 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c b/drivers/gpu/drm/tidss/tidss_dispc.c
index 34bafe951924..c24c06cae10b 100644
--- a/drivers/gpu/drm/tidss/tidss_dispc.c
+++ b/drivers/gpu/drm/tidss/tidss_dispc.c
@@ -1317,10 +1317,12 @@ unsigned int dispc_pclk_diff(unsigned long rate, unsigned long real_rate)
 }
 
 static int check_pixel_clock(struct dispc_device *dispc, u32 hw_videoport,
 			     unsigned long clock)
 {
+	struct tidss_device *tidss = dispc->tidss;
+	struct drm_device *dev = &tidss->ddev;
 	unsigned long round_clock;
 
 	/*
 	 * For VP's with external clocking, clock operations must be
 	 * delegated to respective driver, so we skip the check here.
@@ -1331,51 +1333,65 @@ static int check_pixel_clock(struct dispc_device *dispc, u32 hw_videoport,
 	round_clock = clk_round_rate(dispc->vp_clk[hw_videoport], clock);
 	/*
 	 * To keep the check consistent with dispc_vp_set_clk_rate(), we
 	 * use the same 5% check here.
 	 */
-	if (dispc_pclk_diff(clock, round_clock) > 5)
+	if (dispc_pclk_diff(clock, round_clock) > 5) {
+		drm_dbg(dev, "Mode pixel clock below hardware minimum pixel clock.");
 		return -EINVAL;
+	}
 
 	return 0;
 }
 
 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;
 
 	bus_type = dispc->feat->vp_bus_type[hw_videoport];
 
-	if (WARN_ON(bus_type == DISPC_VP_TIED_OFF))
+	if (WARN_ON(bus_type == DISPC_VP_TIED_OFF)) {
+		drm_dbg(dev, "Invalid bus type.");
 		return MODE_BAD;
+	}
 
-	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;
+	}
 
 	if (check_pixel_clock(dispc, hw_videoport, mode->clock * 1000))
 		return MODE_CLOCK_RANGE;
 
 	/* TODO: add interlace support */
-	if (mode->flags & DRM_MODE_FLAG_INTERLACE)
+	if (mode->flags & DRM_MODE_FLAG_INTERLACE) {
+		drm_dbg(dev, "Interlace modes not supported.");
 		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;
 
@@ -1383,29 +1399,40 @@ 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)
 {

-- 
2.53.0