drm/i915/dsi: clarify GPIO exec sequence

With the various sequence versions and pointer increments interleaved,
it's a bit hard to decipher what's going on. Add separate paths for
different sequence versions.

Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231103201831.1037416-4-andriy.shevchenko@linux.intel.com

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

@@ -456,26 +456,29 @@ static const u8 *mipi_exec_gpio(struct intel_dsi *intel_dsi, const u8 *data)
 	struct drm_device *dev = intel_dsi->base.base.dev;
 	struct drm_i915_private *i915 = to_i915(dev);
 	struct intel_connector *connector = intel_dsi->attached_connector;
-	u8 gpio_source, gpio_index = 0, gpio_number;
+	u8 gpio_source = 0, gpio_index = 0, gpio_number;
 	bool value;
+	int size;
 	bool native = DISPLAY_VER(i915) >= 11;
 
-	if (connector->panel.vbt.dsi.seq_version >= 3)
-		gpio_index = *data++;
+	if (connector->panel.vbt.dsi.seq_version >= 3) {
+		size = 3;
 
-	gpio_number = *data++;
+		gpio_index = data[0];
+		gpio_number = data[1];
+		value = data[2] & BIT(0);
 
-	/* gpio source in sequence v2 only */
-	if (connector->panel.vbt.dsi.seq_version == 2)
-		gpio_source = (*data >> 1) & 3;
-	else
-		gpio_source = 0;
+		if (connector->panel.vbt.dsi.seq_version >= 4 && data[2] & BIT(1))
+			native = false;
+	} else {
+		size = 2;
 
-	if (connector->panel.vbt.dsi.seq_version >= 4 && *data & BIT(1))
-		native = false;
+		gpio_number = data[0];
+		value = data[1] & BIT(0);
 
-	/* pull up/down */
-	value = *data++ & 1;
+		if (connector->panel.vbt.dsi.seq_version == 2)
+			gpio_source = (data[1] >> 1) & 3;
+	}
 
 	drm_dbg_kms(&i915->drm, "GPIO index %u, number %u, source %u, native %s, set to %s\n",
 		    gpio_index, gpio_number, gpio_source, str_yes_no(native), str_on_off(value));
@@ -491,7 +494,7 @@ static const u8 *mipi_exec_gpio(struct intel_dsi *intel_dsi, const u8 *data)
 	else
 		bxt_exec_gpio(connector, gpio_source, gpio_index, value);
 
-	return data;
+	return data + size;
 }
 
 #ifdef CONFIG_ACPI