drm/i915: Enable scanline read based on frame timestamps

For certain platforms on certain encoders, timings are driven
from port instead of pipe. Thus, we can't rely on pipe scanline
registers to get the timing information. Some cases scanline
register read will not be functional.
This is causing vblank evasion logic to fail since it relies on
scanline, causing atomic update failure warnings.

This patch uses pipe framestamp and current timestamp registers
to calculate scanline. This is an indirect way to get the scanline.
It helps resolve atomic update failure for gen9 dsi platforms.

v2: Addressed Ville and Daniel's review comments. Updated the
register MACROs, handled race condition for register reads,
extracted timings from the hwmode. Removed the dependency on
crtc->config to get the encoder type.

v3: Made get scanline function generic

v4: Addressed Ville's review comments. Added a flag to decide timestamp
based scanline reporting. Changed 64bit variables to u32

v5: Adressed Ville's review comments. Put the scanline compute function
at the place of caller. Removed hwmode flags from uapi and used a local
i915 data structure instead.

v6: Used vblank hwmode to get the timings.

v7: Fixed sparse warnings, indentation and minor review comments.

v8: Limited this only for Gen9 DSI.

Credits-to: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NUma Shankar <uma.shankar@intel.com>
Signed-off-by: NChandra Konduru <chandra.konduru@intel.com>
Signed-off-by: NVidya Srinivas <vidya.srinivas@intel.com>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1506347761-4201-1-git-send-email-vidya.srinivas@intel.com

drivers/gpu/drm/i915/i915_irq.c

@@ -783,6 +783,57 @@ static u32 g4x_get_vblank_counter(struct drm_device *dev, unsigned int pipe)
 	return I915_READ(PIPE_FRMCOUNT_G4X(pipe));
 }
 
+/*
+ * On certain encoders on certain platforms, pipe
+ * scanline register will not work to get the scanline,
+ * since the timings are driven from the PORT or issues
+ * with scanline register updates.
+ * This function will use Framestamp and current
+ * timestamp registers to calculate the scanline.
+ */
+static u32 __intel_get_crtc_scanline_from_timestamp(struct intel_crtc *crtc)
+{
+	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
+	struct drm_vblank_crtc *vblank =
+		&crtc->base.dev->vblank[drm_crtc_index(&crtc->base)];
+	const struct drm_display_mode *mode = &vblank->hwmode;
+	u32 vblank_start = mode->crtc_vblank_start;
+	u32 vtotal = mode->crtc_vtotal;
+	u32 htotal = mode->crtc_htotal;
+	u32 clock = mode->crtc_clock;
+	u32 scanline, scan_prev_time, scan_curr_time, scan_post_time;
+
+	/*
+	 * To avoid the race condition where we might cross into the
+	 * next vblank just between the PIPE_FRMTMSTMP and TIMESTAMP_CTR
+	 * reads. We make sure we read PIPE_FRMTMSTMP and TIMESTAMP_CTR
+	 * during the same frame.
+	 */
+	do {
+		/*
+		 * This field provides read back of the display
+		 * pipe frame time stamp. The time stamp value
+		 * is sampled at every start of vertical blank.
+		 */
+		scan_prev_time = I915_READ_FW(PIPE_FRMTMSTMP(crtc->pipe));
+
+		/*
+		 * The TIMESTAMP_CTR register has the current
+		 * time stamp value.
+		 */
+		scan_curr_time = I915_READ_FW(IVB_TIMESTAMP_CTR);
+
+		scan_post_time = I915_READ_FW(PIPE_FRMTMSTMP(crtc->pipe));
+	} while (scan_post_time != scan_prev_time);
+
+	scanline = div_u64(mul_u32_u32(scan_curr_time - scan_prev_time,
+					clock), 1000 * htotal);
+	scanline = min(scanline, vtotal - 1);
+	scanline = (scanline + vblank_start) % vtotal;
+
+	return scanline;
+}
+
 /* I915_READ_FW, only for fast reads of display block, no need for forcewake etc. */
 static int __intel_get_crtc_scanline(struct intel_crtc *crtc)
 {
@@ -799,6 +850,9 @@ static int __intel_get_crtc_scanline(struct intel_crtc *crtc)
 	vblank = &crtc->base.dev->vblank[drm_crtc_index(&crtc->base)];
 	mode = &vblank->hwmode;
 
+	if (mode->private_flags & I915_MODE_FLAG_GET_SCANLINE_FROM_TIMESTAMP)
+		return __intel_get_crtc_scanline_from_timestamp(crtc);
+
 	vtotal = mode->crtc_vtotal;
 	if (mode->flags & DRM_MODE_FLAG_INTERLACE)
 		vtotal /= 2;

drivers/gpu/drm/i915/i915_reg.h

@@ -8808,6 +8808,15 @@ enum skl_power_gate {
 #define MIPIO_TXESC_CLK_DIV2			_MMIO(0x160008)
 #define  GLK_TX_ESC_CLK_DIV2_MASK			0x3FF
 
+/* Gen4+ Timestamp and Pipe Frame time stamp registers */
+#define GEN4_TIMESTAMP		_MMIO(0x2358)
+#define ILK_TIMESTAMP_HI	_MMIO(0x70070)
+#define IVB_TIMESTAMP_CTR	_MMIO(0x44070)
+
+#define _PIPE_FRMTMSTMP_A		0x70048
+#define PIPE_FRMTMSTMP(pipe)		\
+			_MMIO_PIPE2(pipe, _PIPE_FRMTMSTMP_A)
+
 /* BXT MIPI clock controls */
 #define BXT_MAX_VAR_OUTPUT_KHZ			39500
 

drivers/gpu/drm/i915/intel_drv.h

@@ -494,6 +494,8 @@ struct intel_crtc_scaler_state {
 
 /* drm_mode->private_flags */
 #define I915_MODE_FLAG_INHERITED 1
+/* Flag to get scanline using frame time stamps */
+#define I915_MODE_FLAG_GET_SCANLINE_FROM_TIMESTAMP (1<<1)
 
 struct intel_pipe_wm {
 	struct intel_wm_level wm[5];

drivers/gpu/drm/i915/intel_dsi.c

@@ -330,6 +330,10 @@ static bool intel_dsi_compute_config(struct intel_encoder *encoder,
 	adjusted_mode->flags = 0;
 
 	if (IS_GEN9_LP(dev_priv)) {
+		/* Enable Frame time stamp based scanline reporting */
+		adjusted_mode->private_flags |=
+			I915_MODE_FLAG_GET_SCANLINE_FROM_TIMESTAMP;
+
 		/* Dual link goes to DSI transcoder A. */
 		if (intel_dsi->ports == BIT(PORT_C))
 			pipe_config->cpu_transcoder = TRANSCODER_DSI_C;
@@ -1102,6 +1106,10 @@ static void bxt_dsi_get_pipe_config(struct intel_encoder *encoder,
 				pixel_format_from_register_bits(fmt));
 	bpp = pipe_config->pipe_bpp;
 
+	/* Enable Frame time stamo based scanline reporting */
+	adjusted_mode->private_flags |=
+			I915_MODE_FLAG_GET_SCANLINE_FROM_TIMESTAMP;
+
 	/* In terms of pixels */
 	adjusted_mode->crtc_hdisplay =
 				I915_READ(BXT_MIPI_TRANS_HACTIVE(port));