drm/tidss: Fix dss reset

The probe function calls dispc_softreset() before runtime PM is enabled
and without enabling any of the DSS clocks. This happens to work by
luck, and we need to make sure the DSS HW is active and the fclk is
enabled.

To fix the above, add a new function, dispc_init_hw(), which does:

- pm_runtime_set_active()
- clk_prepare_enable(fclk)
- dispc_softreset().

This ensures that the reset can be successfully accomplished.

Note that we use pm_runtime_set_active(), not the normal
pm_runtime_get(). The reason for this is that at this point we haven't
enabled the runtime PM yet and also we don't want the normal resume
callback to be called: the dispc resume callback does some initial HW
setup, and it expects that the HW was off (no video ports are
streaming). If the bootloader has enabled the DSS and has set up a
boot time splash-screen, the DSS would be enabled and streaming which
might lead to issues with the normal resume callback.

Fixes: c9b2d923 ("drm/tidss: Soft Reset DISPC on startup")
Reviewed-by: Aradhya Bhatia <a-bhatia1@ti.com>
Link: https://lore.kernel.org/r/20231109-tidss-probe-v2-8-ac91b5ea35c0@ideasonboard.comSigned-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>

drivers/gpu/drm/tidss/tidss_dispc.c

@@ -2797,6 +2797,49 @@ static int dispc_softreset(struct dispc_device *dispc)
 	return 0;
 }
 
+static int dispc_init_hw(struct dispc_device *dispc)
+{
+	struct device *dev = dispc->dev;
+	int ret;
+
+	ret = pm_runtime_set_active(dev);
+	if (ret) {
+		dev_err(dev, "Failed to set DSS PM to active\n");
+		return ret;
+	}
+
+	ret = clk_prepare_enable(dispc->fclk);
+	if (ret) {
+		dev_err(dev, "Failed to enable DSS fclk\n");
+		goto err_runtime_suspend;
+	}
+
+	ret = dispc_softreset(dispc);
+	if (ret)
+		goto err_clk_disable;
+
+	clk_disable_unprepare(dispc->fclk);
+	ret = pm_runtime_set_suspended(dev);
+	if (ret) {
+		dev_err(dev, "Failed to set DSS PM to suspended\n");
+		return ret;
+	}
+
+	return 0;
+
+err_clk_disable:
+	clk_disable_unprepare(dispc->fclk);
+
+err_runtime_suspend:
+	ret = pm_runtime_set_suspended(dev);
+	if (ret) {
+		dev_err(dev, "Failed to set DSS PM to suspended\n");
+		return ret;
+	}
+
+	return ret;
+}
+
 int dispc_init(struct tidss_device *tidss)
 {
 	struct device *dev = tidss->dev;
@@ -2906,7 +2949,7 @@ int dispc_init(struct tidss_device *tidss)
 	of_property_read_u32(dispc->dev->of_node, "max-memory-bandwidth",
 			     &dispc->memory_bandwidth_limit);
 
-	r = dispc_softreset(dispc);
+	r = dispc_init_hw(dispc);
 	if (r)
 		return r;