drm/i915/dsi: Use unconditional msleep for the panel_on_delay when there is no...

drm/i915/dsi: Use unconditional msleep for the panel_on_delay when there is no reset-deassert MIPI-sequence

Commit 25b4620e ("drm/i915/dsi: Skip delays for v3 VBTs in vid-mode")
added an intel_dsi_msleep() helper which skips sleeping if the
MIPI-sequences have a version of 3 or newer and the panel is in vid-mode;
and it moved a bunch of msleep-s over to this new helper.

This was based on my reading of the big comment around line 730 which
starts with "Panel enable/disable sequences from the VBT spec.",
where the "v3 video mode seq" column does not have any wait t# entries.

Given that this code has been used on a lot of different devices without
issues until now, it seems that my interpretation of the spec here is
mostly correct.

But now I have encountered one device, an Acer Aspire Switch 10 E
SW3-016, where the panel will not light up unless we do actually honor the
panel_on_delay after exexuting the MIPI_SEQ_PANEL_ON sequence.

What seems to set this model apart is that it is lacking a
MIPI_SEQ_DEASSERT_RESET sequence, which is where the power-on
delay usually happens.

Fix the panel not lighting up on this model by using an unconditional
msleep(panel_on_delay) instead of intel_dsi_msleep() when there is
no MIPI_SEQ_DEASSERT_RESET sequence.

Fixes: 25b4620e ("drm/i915/dsi: Skip delays for v3 VBTs in vid-mode")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201118124058.26021-1-hdegoede@redhat.com

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

@@ -812,10 +812,20 @@ static void intel_dsi_pre_enable(struct intel_atomic_state *state,
 		intel_dsi_prepare(encoder, pipe_config);
 
 	intel_dsi_vbt_exec_sequence(intel_dsi, MIPI_SEQ_POWER_ON);
-	intel_dsi_msleep(intel_dsi, intel_dsi->panel_on_delay);
 
-	/* Deassert reset */
+	/*
+	 * Give the panel time to power-on and then deassert its reset.
+	 * Depending on the VBT MIPI sequences version the deassert-seq
+	 * may contain the necessary delay, intel_dsi_msleep() will skip
+	 * the delay in that case. If there is no deassert-seq, then an
+	 * unconditional msleep is used to give the panel time to power-on.
+	 */
+	if (dev_priv->vbt.dsi.sequence[MIPI_SEQ_DEASSERT_RESET]) {
+		intel_dsi_msleep(intel_dsi, intel_dsi->panel_on_delay);
 		intel_dsi_vbt_exec_sequence(intel_dsi, MIPI_SEQ_DEASSERT_RESET);
+	} else {
+		msleep(intel_dsi->panel_on_delay);
+	}
 
 	if (IS_GEMINILAKE(dev_priv)) {
 		glk_cold_boot = glk_dsi_enable_io(encoder);