drm/tidss: Add simple K2G manual reset

K2G display controller does not support soft reset, but we can do the
most important steps manually: mask the IRQs and disable the VPs.
Reviewed-by: Aradhya Bhatia <a-bhatia1@ti.com>
Link: https://lore.kernel.org/r/20231109-tidss-probe-v2-7-ac91b5ea35c0@ideasonboard.comSigned-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>

drivers/gpu/drm/tidss/tidss_dispc.c

@@ -2761,14 +2761,28 @@ static void dispc_init_errata(struct dispc_device *dispc)
 	}
 }
 
+/*
+ * K2G display controller does not support soft reset, so we do a basic manual
+ * reset here: make sure the IRQs are masked and VPs are disabled.
+ */
+static void dispc_softreset_k2g(struct dispc_device *dispc)
+{
+	dispc_set_irqenable(dispc, 0);
+	dispc_read_and_clear_irqstatus(dispc);
+
+	for (unsigned int vp_idx = 0; vp_idx < dispc->feat->num_vps; ++vp_idx)
+		VP_REG_FLD_MOD(dispc, vp_idx, DISPC_VP_CONTROL, 0, 0, 0);
+}
+
 static int dispc_softreset(struct dispc_device *dispc)
 {
 	u32 val;
 	int ret;
 
-	/* K2G display controller does not support soft reset */
-	if (dispc->feat->subrev == DISPC_K2G)
+	if (dispc->feat->subrev == DISPC_K2G) {
+		dispc_softreset_k2g(dispc);
 		return 0;
+	}
 
 	/* Soft reset */
 	REG_FLD_MOD(dispc, DSS_SYSCONFIG, 1, 1, 1);