drm/i915/psr: Calculate IO wake and fast wake lines for DISPLAY_VER < 12

Bspec mentions 50 us for IO wake time and 32 us for fast wake time. 32 us
is most probably wrong as it doesn't meet the specification as fast wake
time is calculated in Bspec like this:

10..16 us (precharge) + 8 us (preamble) + 4 us (phy_wake) + 20 us
(tfw_exit_latency)

Instead of using these constants calculate IO wake and fast wake for
DISPLAY_VER < 12 as well.

v3:
  - do not handle < 9 separately
  - add own helper for skl and tgl io buffer wake times
v2:
  - initialize io/fast_wake_time for display version < 9
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240313133221.868391-4-jouni.hogander@intel.com

drivers/gpu/drm/i915/display/intel_psr.c

@@ -1150,36 +1150,52 @@ static bool _lnl_compute_alpm_params(struct intel_dp *intel_dp,
 	return true;
 }
 
-static int io_buffer_wake_time(void)
+/*
+ * IO wake time for DISPLAY_VER < 12 is not directly mentioned in Bspec. There
+ * are 50 us io wake time and 32 us fast wake time. Clearly preharge pulses are
+ * not (improperly) included in 32 us fast wake time. 50 us - 32 us = 18 us.
+ */
+static int skl_io_buffer_wake_time(void)
+{
+	return 18;
+}
+
+static int tgl_io_buffer_wake_time(void)
 {
 	return 10;
 }
 
+static int io_buffer_wake_time(const struct intel_crtc_state *crtc_state)
+{
+	struct drm_i915_private *i915 = to_i915(crtc_state->uapi.crtc->dev);
+
+	if (DISPLAY_VER(i915) >= 12)
+		return tgl_io_buffer_wake_time();
+	else
+		return skl_io_buffer_wake_time();
+}
+
 static bool _compute_alpm_params(struct intel_dp *intel_dp,
 				 struct intel_crtc_state *crtc_state)
 {
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 	int io_wake_lines, io_wake_time, fast_wake_lines, fast_wake_time;
-	u8 max_wake_lines;
-
-	if (DISPLAY_VER(i915) >= 12) {
 	int tfw_exit_latency = 20; /* eDP spec */
 	int phy_wake = 4;	   /* eDP spec */
 	int preamble = 8;	   /* eDP spec */
 	int precharge = intel_dp_aux_fw_sync_len() - preamble;
+	u8 max_wake_lines;
 
-		io_wake_time = max(precharge, io_buffer_wake_time()) + preamble +
-			phy_wake + tfw_exit_latency;
+	io_wake_time = max(precharge, io_buffer_wake_time(crtc_state)) +
+		preamble + phy_wake + tfw_exit_latency;
 	fast_wake_time = precharge + preamble + phy_wake +
 		tfw_exit_latency;
 
+	if (DISPLAY_VER(i915) >= 12)
 		/* TODO: Check how we can use ALPM_CTL fast wake extended field */
 		max_wake_lines = 12;
-	} else {
-		io_wake_time = 50;
-		fast_wake_time = 32;
+	else
 		max_wake_lines = 8;
-	}
 
 	io_wake_lines = intel_usecs_to_scanlines(
 		&crtc_state->hw.adjusted_mode, io_wake_time);