[PATCH v8 6/8] drm/sun4i: sun6i_mipi_dsi: Set proper vblk timing calculation

[Jagan Teki <jagan@amarulasolutions.com>]

Like other dsi setup timings, or hblk for that matter vblk would
also require compute the timings based payload equation along with
packet overhead.

But, on the other hand vblk computation is also depends on device
lane number.
- for 4 lane devices, it is computed based on vtotal, packet overhead
  along with hblk value.
- for others devices, it is simply 0

BSP code from BPI-M64-bsp is computing vblk as for 4-lane devices
(from linux-sunxi
drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c)

tmp = (ht*dsi_pixel_bits[format]/8)*vt-(4+dsi_hblk+2);
dsi_vblk = (lane-tmp%lane);

So, update the vblk timing calculation accordingly.

Tested on 2-lane, 4-lane MIPI-DSI LCD panels.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
---
 drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 29 +++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
index a64e6ec00f22..a08dfdcbe9e8 100644
--- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
+++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
@@ -446,6 +446,27 @@ static void sun6i_dsi_setup_format(struct sun6i_dsi *dsi,
 		     SUN6I_DSI_PIXEL_CTL0_FORMAT(fmt));
 }
 
+static u16 sun6i_dsi_get_timings_vblk(struct sun6i_dsi *dsi,
+				      struct drm_display_mode *mode, u16 hblk)
+{
+	struct mipi_dsi_device *device = dsi->device;
+	unsigned int Bpp = mipi_dsi_pixel_format_to_bpp(device->format) / 8;
+	int tmp;
+
+	if (device->lanes != 4)
+		return 0;
+
+	/*
+	 * The vertical blank is set using a blanking packet (4 bytes +
+	 * payload + 2 bytes). Its minimal size is therefore 6 bytes
+	 */
+#define VBLK_PACKET_OVERHEAD	6
+	tmp = (mode->htotal * Bpp) * mode->vtotal -
+	      (hblk + VBLK_PACKET_OVERHEAD);
+
+	return (device->lanes - tmp % device->lanes);
+}
+
 static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
 				    struct drm_display_mode *mode)
 {
@@ -493,13 +514,7 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
 		   (mode->htotal - (mode->hsync_end - mode->hsync_start)) *
 		   Bpp - HBLK_PACKET_OVERHEAD);
 
-	/*
-	 * And I'm not entirely sure what vblk is about. The driver in
-	 * Allwinner BSP is using a rather convoluted calculation
-	 * there only for 4 lanes. However, using 0 (the !4 lanes
-	 * case) even with a 4 lanes screen seems to work...
-	 */
-	vblk = 0;
+	vblk = sun6i_dsi_get_timings_vblk(dsi, mode, hblk);
 
 	/* How many bytes do we need to send all payloads? */
 	bytes = max_t(size_t, max(max(hfp, hblk), max(hsa, hbp)), vblk);
-- 
2.18.0.321.gffc6fa0e3


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