Re: [PATCH V2 2/3] OMAPDSS: DISPC: Handle synclost errors in OMAP3

In OMAP3 DISPC video overlays suffer from some undocumented horizontal position
and timing related limitations leading to SYNCLOST errors. Whenever the image
window is moved towards the right of the screen SYNCLOST errors become
frequent. Checks have been implemented to see that DISPC driver rejects
configuration exceeding above limitations.

This code was successfully tested on OMAP3. This code is written based on code
written by Ville Syrjälä [off-list ref] in Linux OMAP kernel. Ville
Syrjälä [off-list ref] had added checks for video overlay horizontal
timing and DISPC horizontal blanking length limitations.

Signed-off-by: Chandrabhanu Mahapatra <redacted>
---
 drivers/video/omap2/dss/dispc.c |   97 +++++++++++++++++++++++++++++----------
 1 files changed, 72 insertions(+), 25 deletions(-)

diff --git a/drivers/video/omap2/dss/dispc.c b/drivers/video/omap2/dss/dispc.c
index 5a1963e..d8a1672 100644
--- a/drivers/video/omap2/dss/dispc.c
+++ b/drivers/video/omap2/dss/dispc.c

@@ -1622,6 +1622,57 @@ static void calc_dma_rotation_offset(u8 rotation, bool mirror,
 	}
 }
 
+static int check_horiz_timing(enum omap_channel channel, u16 pos_x,
+		u16 width, u16 height, u16 out_width, u16 out_height)

+{
+	int DS = DIV_ROUND_UP(height, out_height);
+	struct omap_dss_device *dssdev = dispc_mgr_get_device(channel);
+	struct omap_video_timings t = dssdev->panel.timings;
+	unsigned long nonactive, lclk, pclk;
+	static const u8 limits[3] = { 8, 10, 20 };
+	u64 val, blank;
+	int i;
+
+	nonactive = t.x_res + t.hfp + t.hsw + t.hbp - out_width;
+	pclk = dispc_mgr_pclk_rate(channel);
+	lclk = dispc_mgr_lclk_rate(channel);
+
+	i = 0;
+	if (out_height < height)
+		i++;
+	if (out_width < width)
+		i++;
+	blank = div_u64((u64)(t.hbp + t.hsw + t.hfp) * lclk, pclk);
+	DSSDBG("blanking period + ppl = %llu (limit = %u)\n", blank, limits[i]);
+	if (blank <= limits[i])
+		return -EINVAL;
+
+	/*
+	 * Pixel data should be prepared before visible display point starts.
+	 * So, atleast DS-2 lines must have already been fetched by DISPC
+	 * during nonactive - pos_x period.
+	 */
+	val = div_u64((u64)(nonactive - pos_x) * lclk, pclk);
+	DSSDBG("(nonactive - pos_x) * pcd = %llu,"
+		" max(0, DS - 2) * width = %d\n",
+		val, max(0, DS - 2) * width);
+	if (val < max(0, DS - 2) * width)
+		return -EINVAL;
+
+	/*
+	 * All lines need to be refilled during the nonactive period of which
+	 * only one line can be loaded during the active period. So, atleast
+	 * DS - 1 lines should be loaded during nonactive period.
+	 */
+	val =  div_u64((u64)nonactive * lclk, pclk);
+	DSSDBG("nonactive * pcd  = %llu, max(0, DS - 1) * width = %d\n",
+		val, max(0, DS - 1) * width);
+	if (val < max(0, DS - 1) * width)
+		return -EINVAL;
+
+	return 0;
+}
+
 static unsigned long calc_fclk_five_taps(enum omap_channel channel, u16 width,
 		u16 height, u16 out_width, u16 out_height,
 		enum omap_color_mode color_mode)

@@ -1702,7 +1753,7 @@ static int dispc_ovl_calc_scaling(enum omap_plane plane,
 		enum omap_channel channel, u16 width, u16 height,
 		u16 out_width, u16 out_height,
 		enum omap_color_mode color_mode, bool *five_taps,
-		int *x_predecim, int *y_predecim)
+		int *x_predecim, int *y_predecim, u16 pos_x)
 {
 	struct omap_overlay *ovl = omap_dss_get_overlay(plane);
 	const int maxdownscale = dss_feat_get_param_max(FEAT_PARAM_DOWNSCALE);

@@ -1778,6 +1829,9 @@ static int dispc_ovl_calc_scaling(enum omap_plane plane,
 			fclk = calc_fclk_five_taps(channel, in_width, in_height,
 				out_width, out_height, color_mode);
 
+			error = check_horiz_timing(channel, pos_x, in_width,
+				in_height, out_width, out_height);
+
 			if (in_width > maxsinglelinewidth)
 				if (in_height > out_height &&
 					in_height < out_height * 2)

@@ -1785,7 +1839,7 @@ static int dispc_ovl_calc_scaling(enum omap_plane plane,
 			if (!*five_taps)
 				fclk = calc_fclk(channel, in_width, in_height,
 					out_width, out_height);
-			error = (in_width > maxsinglelinewidth * 2 ||
+			error = (error || in_width > maxsinglelinewidth * 2 ||
 				(in_width > maxsinglelinewidth && *five_taps) ||
 				!fclk || fclk > dispc_fclk_rate());
 			if (error) {

@@ -1801,6 +1855,12 @@ static int dispc_ovl_calc_scaling(enum omap_plane plane,
 		} while (decim_x <= *x_predecim && decim_y <= *y_predecim
 			&& error);
 
+		if (check_horiz_timing(channel, pos_x, width, height,
+			out_width, out_height)){
+				DSSERR("horizontal timing too tight\n");
+				return -EINVAL;
+		}
+
 		if (in_width > (maxsinglelinewidth * 2)) {
 			DSSERR("Cannot setup scaling");
 			DSSERR("width exceeds maximum width possible");

@@ -1901,7 +1961,7 @@ int dispc_ovl_setup(enum omap_plane plane, struct omap_overlay_info *oi,
 
 	r = dispc_ovl_calc_scaling(plane, channel, in_width, in_height,
 			out_width, out_height, oi->color_mode, &five_taps,
-			&x_predecim, &y_predecim);
+			&x_predecim, &y_predecim, oi->pos_x);
 	if (r)
 		return r;
 

@@ -2472,32 +2532,19 @@ unsigned long dispc_fclk_rate(void)
 
 unsigned long dispc_mgr_lclk_rate(enum omap_channel channel)
 {
-	struct platform_device *dsidev;
-	int lcd;
-	unsigned long r;
-	u32 l;
+	unsigned long r = dispc_fclk_rate();
 
-	l = dispc_read_reg(DISPC_DIVISORo(channel));
+	if (dispc_mgr_is_lcd(channel)) {
+		u32 l;
+		int lcd;
 
-	lcd = FLD_GET(l, 23, 16);
+		l = dispc_read_reg(DISPC_DIVISORo(channel));
+		lcd = FLD_GET(l, 23, 16);
 
-	switch (dss_get_lcd_clk_source(channel)) {
-	case OMAP_DSS_CLK_SRC_FCK:
-		r = clk_get_rate(dispc.dss_clk);
-		break;
-	case OMAP_DSS_CLK_SRC_DSI_PLL_HSDIV_DISPC:
-		dsidev = dsi_get_dsidev_from_id(0);
-		r = dsi_get_pll_hsdiv_dispc_rate(dsidev);
-		break;
-	case OMAP_DSS_CLK_SRC_DSI2_PLL_HSDIV_DISPC:
-		dsidev = dsi_get_dsidev_from_id(1);
-		r = dsi_get_pll_hsdiv_dispc_rate(dsidev);
-		break;
-	default:
-		BUG();
+		return r / lcd;
+	} else {
+		return r;
 	}
-
-	return r / lcd;
 }