drm/mcde: Some fixes to handling video mode

The video DSI mode had not really been tested. These fixes makes
it more likely to work on real hardware:
- Put the active width (x width) in the right bits and the VSA
  (vertical sync active) in the right bits (those were swapped).
- Calculate the packet sizes in bytes as in the vendor driver,
  rather than in bits. Test the calculations agains a
  spreadsheet and confirmed by debug prints to be reasonable.
- Also verified the register values with relative confidence
  to register dumps from the Samsung GT-I8190 boot loader
  graphics. We are not identical but not off by far either.
- Error out if the current mode and refresh frequency doesn't
  work out. (In the future we may simply want to scale down
  the vrefresh.)
- Handle negative result in front/back/sync packages and fall
  back to zero like in the vendor driver.
- Put in lots of clarifying comments and references to the
  documentation where the code is hard to understand.
- Set the DSI_VID_VCA_SETTING2 field
  DSI_VID_VCA_SETTING2_MAX_LINE_LIMIT to blkline_pck - 6 as in
  the vendor driver and mask the field properly.
- Set the DSI_VID_VCA_SETTING1 field
  DSI_VID_VCA_SETTING1_MAX_BURST_LIMIT to blkeol_pck - 6 to
  blkeol_duration - 6 as in the vendor driver.

Cc: Stephan Gerhold <stephan@gerhold.net>
Fixes: 5fc537bf ("drm/mcde: Add new driver for ST-Ericsson MCDE")
Link: https://patchwork.freedesktop.org/patch/msgid/20191217150959.17215-1-linus.walleij@linaro.orgReviewed-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpu/drm/mcde/mcde_dsi.c

@@ -388,13 +388,14 @@ void mcde_dsi_te_request(struct mipi_dsi_device *mdsi)
 static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,
 				      const struct drm_display_mode *mode)
 {
-	u8 bpp = mipi_dsi_pixel_format_to_bpp(d->mdsi->format);
+	/* cpp, characters per pixel, number of bytes per pixel */
+	u8 cpp = mipi_dsi_pixel_format_to_bpp(d->mdsi->format) / 8;
+	u64 pclk;
 	u64 bpl;
-	u32 hfp;
-	u32 hbp;
-	u32 hsa;
+	int hfp;
+	int hbp;
+	int hsa;
 	u32 blkline_pck, line_duration;
-	u32 blkeol_pck, blkeol_duration;
 	u32 val;
 
 	val = 0;
@@ -431,11 +432,21 @@ static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,
 		return;
 	}
 
-	/* TODO: TVG could be enabled here */
+	/* TODO: TVG (test video generator) could be enabled here */
 
-	/* Send blanking packet */
+	/*
+	 * During vertical blanking: go to LP mode
+	 * Like with the EOL setting, if this is not set, the EOL area will be
+	 * filled with NULL or blanking packets in the vblank area.
+	 * FIXME: some Samsung phones and display panels such as s6e63m0 use
+	 * DSI_VID_MAIN_CTL_REG_BLKLINE_MODE_BLANKING here instead,
+	 * figure out how to properly configure that from the panel.
+	 */
 	val |= DSI_VID_MAIN_CTL_REG_BLKLINE_MODE_LP_0;
-	/* Send EOL packet */
+	/*
+	 * During EOL: go to LP mode. If this is not set, the EOL area will be
+	 * filled with NULL or blanking packets.
+	 */
 	val |= DSI_VID_MAIN_CTL_REG_BLKEOL_MODE_LP_0;
 	/* Recovery mode 1 */
 	val |= 1 << DSI_VID_MAIN_CTL_RECOVERY_MODE_SHIFT;
@@ -443,13 +454,13 @@ static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,
 	writel(val, d->regs + DSI_VID_MAIN_CTL);
 
 	/* Vertical frame parameters are pretty straight-forward */
-	val = mode->vdisplay << DSI_VID_VSIZE_VSA_LENGTH_SHIFT;
+	val = mode->vdisplay << DSI_VID_VSIZE_VACT_LENGTH_SHIFT;
 	/* vertical front porch */
 	val |= (mode->vsync_start - mode->vdisplay)
 		<< DSI_VID_VSIZE_VFP_LENGTH_SHIFT;
 	/* vertical sync active */
 	val |= (mode->vsync_end - mode->vsync_start)
-		<< DSI_VID_VSIZE_VACT_LENGTH_SHIFT;
+		<< DSI_VID_VSIZE_VSA_LENGTH_SHIFT;
 	/* vertical back porch */
 	val |= (mode->vtotal - mode->vsync_end)
 		<< DSI_VID_VSIZE_VBP_LENGTH_SHIFT;
@@ -457,36 +468,54 @@ static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,
 
 	/*
 	 * Horizontal frame parameters:
-	 * horizontal resolution is given in pixels and must be re-calculated
-	 * into bytes since this is what the hardware expects.
+	 * horizontal resolution is given in pixels but must be re-calculated
+	 * into bytes since this is what the hardware expects, these registers
+	 * define the payload size of the packet.
+	 *
+	 * hfp = horizontal front porch in bytes
+	 * hbp = horizontal back porch in bytes
+	 * hsa = horizontal sync active in bytes
 	 *
 	 * 6 + 2 is HFP header + checksum
 	 */
-	hfp = (mode->hsync_start - mode->hdisplay) * bpp - 6 - 2;
+	hfp = (mode->hsync_start - mode->hdisplay) * cpp - 6 - 2;
 	if (d->mdsi->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE) {
 		/*
+		 * Use sync pulse for sync: explicit HSA time
 		 * 6 is HBP header + checksum
 		 * 4 is RGB header + checksum
 		 */
-		hbp = (mode->htotal - mode->hsync_end) * bpp - 4 - 6;
+		hbp = (mode->htotal - mode->hsync_end) * cpp - 4 - 6;
 		/*
 		 * 6 is HBP header + checksum
 		 * 4 is HSW packet bytes
 		 * 4 is RGB header + checksum
 		 */
-		hsa = (mode->hsync_end - mode->hsync_start) * bpp - 4 - 4 - 6;
+		hsa = (mode->hsync_end - mode->hsync_start) * cpp - 4 - 4 - 6;
 	} else {
 		/*
-		 * HBP includes both back porch and sync
+		 * Use event for sync: HBP includes both back porch and sync
 		 * 6 is HBP header + checksum
 		 * 4 is HSW packet bytes
 		 * 4 is RGB header + checksum
 		 */
-		hbp = (mode->htotal - mode->hsync_start) * bpp - 4 - 4 - 6;
-		/* HSA is not considered in this mode and set to 0 */
+		hbp = (mode->htotal - mode->hsync_start) * cpp - 4 - 4 - 6;
+		/* HSA is not present in this mode and set to 0 */
 		hsa = 0;
 	}
-	dev_dbg(d->dev, "hfp: %u, hbp: %u, hsa: %u\n",
+	if (hfp < 0) {
+		dev_info(d->dev, "hfp negative, set to 0\n");
+		hfp = 0;
+	}
+	if (hbp < 0) {
+		dev_info(d->dev, "hbp negative, set to 0\n");
+		hbp = 0;
+	}
+	if (hsa < 0) {
+		dev_info(d->dev, "hsa negative, set to 0\n");
+		hsa = 0;
+	}
+	dev_dbg(d->dev, "hfp: %u, hbp: %u, hsa: %u bytes\n",
 		hfp, hbp, hsa);
 
 	/* Frame parameters: horizontal sync active */
@@ -497,71 +526,185 @@ static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,
 	val |= hfp << DSI_VID_HSIZE1_HFP_LENGTH_SHIFT;
 	writel(val, d->regs + DSI_VID_HSIZE1);
 
-	/* RGB data length (bytes on one scanline) */
-	val = mode->hdisplay * (bpp / 8);
+	/* RGB data length (visible bytes on one scanline) */
+	val = mode->hdisplay * cpp;
 	writel(val, d->regs + DSI_VID_HSIZE2);
+	dev_dbg(d->dev, "RGB length, visible area on a line: %u bytes\n", val);
 
-	/* TODO: further adjustments for TVG mode here */
+	/*
+	 * Calculate the time between two pixels in picoseconds using
+	 * the supplied refresh rate and total resolution including
+	 * porches and sync.
+	 */
+	/* (ps/s) / (pixels/s) = ps/pixels */
+	pclk = DIV_ROUND_UP_ULL(1000000000000,
+				(mode->vrefresh * mode->htotal * mode->vtotal));
+	dev_dbg(d->dev, "picoseconds between two pixels: %llu\n",
+		pclk);
 
 	/*
-	 * EOL packet length from bits per line calculations: pixel clock
-	 * is given in kHz, calculate the time between two pixels in
-	 * picoseconds.
+	 * How many bytes per line will this update frequency yield?
+	 *
+	 * Calculate the number of picoseconds for one scanline (1), then
+	 * divide by 1000000000000 (2) to get in pixels per second we
+	 * want to output.
+	 *
+	 * Multiply with number of bytes per second at this video display
+	 * frequency (3) to get number of bytes transferred during this
+	 * time. Notice that we use the frequency the display wants,
+	 * not what we actually get from the DSI PLL, which is hs_freq.
+	 *
+	 * These arithmetics are done in a different order to avoid
+	 * overflow.
 	 */
-	bpl = mode->clock * mode->htotal;
-	bpl *= (d->hs_freq / 8);
-	do_div(bpl, 1000000); /* microseconds */
-	do_div(bpl, 1000000); /* seconds */
+	bpl = pclk * mode->htotal; /* (1) picoseconds per line */
+	dev_dbg(d->dev, "picoseconds per line: %llu\n", bpl);
+	/* Multiply with bytes per second (3) */
+	bpl *= (d->mdsi->hs_rate / 8);
+	/* Pixels per second (2) */
+	bpl = DIV_ROUND_DOWN_ULL(bpl, 1000000); /* microseconds */
+	bpl = DIV_ROUND_DOWN_ULL(bpl, 1000000); /* seconds */
+	/* parallel transactions in all lanes */
 	bpl *= d->mdsi->lanes;
-	dev_dbg(d->dev, "calculated bytes per line: %llu\n", bpl);
+	dev_dbg(d->dev,
+		"calculated bytes per line: %llu @ %d Hz with HS %lu Hz\n",
+		bpl, mode->vrefresh, d->mdsi->hs_rate);
+
 	/*
 	 * 6 is header + checksum, header = 4 bytes, checksum = 2 bytes
 	 * 4 is short packet for vsync/hsync
 	 */
 	if (d->mdsi->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE) {
-		/* Fixme: isn't the hsync width in pixels? */
+		/* Set the event packet size to 0 (not used) */
+		writel(0, d->regs + DSI_VID_BLKSIZE1);
+		/*
+		 * FIXME: isn't the hsync width in pixels? The porch and
+		 * sync area size is in pixels here, but this -6
+		 * seems to be for bytes. It looks like this in the vendor
+		 * code though. Is it completely untested?
+		 */
 		blkline_pck = bpl - (mode->hsync_end - mode->hsync_start) - 6;
 		val = blkline_pck << DSI_VID_BLKSIZE2_BLKLINE_PULSE_PCK_SHIFT;
 		writel(val, d->regs + DSI_VID_BLKSIZE2);
 	} else {
+		/* Set the sync pulse packet size to 0 (not used) */
+		writel(0, d->regs + DSI_VID_BLKSIZE2);
+		/* Specifying payload size in bytes (-4-6 from manual) */
 		blkline_pck = bpl - 4 - 6;
+		if (blkline_pck > 0x1FFF)
+			dev_err(d->dev, "blkline_pck too big %d bytes\n",
+				blkline_pck);
 		val = blkline_pck << DSI_VID_BLKSIZE1_BLKLINE_EVENT_PCK_SHIFT;
+		val &= DSI_VID_BLKSIZE1_BLKLINE_EVENT_PCK_MASK;
 		writel(val, d->regs + DSI_VID_BLKSIZE1);
 	}
 
-	line_duration = (blkline_pck + 6) / d->mdsi->lanes;
-	dev_dbg(d->dev, "line duration %u\n", line_duration);
+	/*
+	 * The line duration is used to scale back the frequency from
+	 * the max frequency supported by the HS clock to the desired
+	 * update frequency in vrefresh.
+	 */
+	line_duration = blkline_pck + 6;
+	/*
+	 * The datasheet contains this complex condition to decreasing
+	 * the line duration by 1 under very specific circumstances.
+	 * Here we also imply that LP is used during burst EOL.
+	 */
+	if (d->mdsi->lanes == 2 && (hsa & 0x01) && (hfp & 0x01)
+	    && (d->mdsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST))
+		line_duration--;
+	line_duration = DIV_ROUND_CLOSEST(line_duration, d->mdsi->lanes);
+	dev_dbg(d->dev, "line duration %u bytes\n", line_duration);
 	val = line_duration << DSI_VID_DPHY_TIME_REG_LINE_DURATION_SHIFT;
 	/*
 	 * This is the time to perform LP->HS on D-PHY
 	 * FIXME: nowhere to get this from: DT property on the DSI?
+	 * The manual says this is "system dependent".
+	 * values like 48 and 72 seen in the vendor code.
 	 */
-	val |= 0 << DSI_VID_DPHY_TIME_REG_WAKEUP_TIME_SHIFT;
+	val |= 48 << DSI_VID_DPHY_TIME_REG_WAKEUP_TIME_SHIFT;
 	writel(val, d->regs + DSI_VID_DPHY_TIME);
 
-	/* Calculate block end of line */
-	blkeol_pck = bpl - mode->hdisplay * bpp - 6;
-	blkeol_duration = (blkeol_pck + 6) / d->mdsi->lanes;
-	dev_dbg(d->dev, "blkeol pck: %u, duration: %u\n",
-		 blkeol_pck, blkeol_duration);
-
+	/*
+	 * See the manual figure 657 page 2203 for understanding the impact
+	 * of the different burst mode settings.
+	 */
 	if (d->mdsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST) {
-		/* Set up EOL clock for burst mode */
+		int blkeol_pck, blkeol_duration;
+		/*
+		 * Packet size at EOL for burst mode, this is only used
+		 * if DSI_VID_MAIN_CTL_REG_BLKEOL_MODE_LP_0 is NOT set,
+		 * but we instead send NULL or blanking packets at EOL.
+		 * This is given in number of bytes.
+		 *
+		 * See the manual page 2198 for the 13 reg_blkeol_pck bits.
+		 */
+		blkeol_pck = bpl - (mode->htotal * cpp) - 6;
+		if (blkeol_pck < 0) {
+			dev_err(d->dev, "video block does not fit on line!\n");
+			dev_err(d->dev,
+				"calculated bytes per line: %llu @ %d Hz\n",
+				bpl, mode->vrefresh);
+			dev_err(d->dev,
+				"bytes per line (blkline_pck) %u bytes\n",
+				blkline_pck);
+			dev_err(d->dev,
+				"blkeol_pck becomes %d bytes\n", blkeol_pck);
+			return;
+		}
+		dev_dbg(d->dev, "BLKEOL packet: %d bytes\n", blkeol_pck);
+
 		val = readl(d->regs + DSI_VID_BLKSIZE1);
+		val &= ~DSI_VID_BLKSIZE1_BLKEOL_PCK_MASK;
 		val |= blkeol_pck << DSI_VID_BLKSIZE1_BLKEOL_PCK_SHIFT;
 		writel(val, d->regs + DSI_VID_BLKSIZE1);
-		writel(blkeol_pck, d->regs + DSI_VID_VCA_SETTING2);
-
-		writel(blkeol_duration, d->regs + DSI_VID_PCK_TIME);
-		writel(blkeol_duration - 6, d->regs + DSI_VID_VCA_SETTING1);
+		/* Use the same value for exact burst limit */
+		val = blkeol_pck <<
+			DSI_VID_VCA_SETTING2_EXACT_BURST_LIMIT_SHIFT;
+		val &= DSI_VID_VCA_SETTING2_EXACT_BURST_LIMIT_MASK;
+		writel(val, d->regs + DSI_VID_VCA_SETTING2);
+		/*
+		 * This BLKEOL duration is claimed to be the duration in clock
+		 * cycles of the BLLP end-of-line (EOL) period for each line if
+		 * DSI_VID_MAIN_CTL_REG_BLKEOL_MODE_LP_0 is set.
+		 *
+		 * It is hard to trust the manuals' claim that this is in clock
+		 * cycles as we mimic the behaviour of the vendor code, which
+		 * appears to write a number of bytes that would have been
+		 * transferred on a single lane.
+		 *
+		 * See the manual figure 657 page 2203 and page 2198 for the 13
+		 * reg_blkeol_duration bits.
+		 *
+		 * FIXME: should this also be set up also for non-burst mode
+		 * according to figure 565 page 2202?
+		 */
+		blkeol_duration = DIV_ROUND_CLOSEST(blkeol_pck + 6,
+						    d->mdsi->lanes);
+		dev_dbg(d->dev, "BLKEOL duration: %d clock cycles\n",
+			blkeol_duration);
+
+		val = readl(d->regs + DSI_VID_PCK_TIME);
+		val &= ~DSI_VID_PCK_TIME_BLKEOL_DURATION_MASK;
+		val |= blkeol_duration <<
+			DSI_VID_PCK_TIME_BLKEOL_DURATION_SHIFT;
+		writel(val, d->regs + DSI_VID_PCK_TIME);
+
+		/* Max burst limit, this is given in bytes */
+		val = readl(d->regs + DSI_VID_VCA_SETTING1);
+		val &= ~DSI_VID_VCA_SETTING1_MAX_BURST_LIMIT_MASK;
+		val |= (blkeol_pck - 6) <<
+			DSI_VID_VCA_SETTING1_MAX_BURST_LIMIT_SHIFT;
+		writel(val, d->regs + DSI_VID_VCA_SETTING1);
 	}
 
 	/* Maximum line limit */
 	val = readl(d->regs + DSI_VID_VCA_SETTING2);
-	val |= blkline_pck <<
-		DSI_VID_VCA_SETTING2_EXACT_BURST_LIMIT_SHIFT;
+	val &= ~DSI_VID_VCA_SETTING2_MAX_LINE_LIMIT_MASK;
+	val |= (blkline_pck - 6) <<
+		DSI_VID_VCA_SETTING2_MAX_LINE_LIMIT_SHIFT;
 	writel(val, d->regs + DSI_VID_VCA_SETTING2);
-
+	dev_dbg(d->dev, "blkline pck: %d bytes\n", blkline_pck - 6);
 }
 
 static void mcde_dsi_start(struct mcde_dsi *d)

drivers/gpu/drm/mcde/mcde_dsi_regs.h

@@ -228,6 +228,7 @@
 
 #define DSI_VID_PCK_TIME 0x000000A8
 #define DSI_VID_PCK_TIME_BLKEOL_DURATION_SHIFT 0
+#define DSI_VID_PCK_TIME_BLKEOL_DURATION_MASK 0x00000FFF
 
 #define DSI_VID_DPHY_TIME 0x000000AC
 #define DSI_VID_DPHY_TIME_REG_LINE_DURATION_SHIFT 0