gpu: ipu-v3: pre: add double buffer status readback

This allows the upper layers to check if a double buffer update has
been applied by the PRE or is still pending.
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
[p.zabel@pengutronix.de: inverted logic: done -> pending]
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

drivers/gpu/ipu-v3/ipu-pre.c

@@ -265,6 +265,12 @@ void ipu_pre_update(struct ipu_pre *pre, unsigned int bufaddr)
 	writel(IPU_PRE_CTRL_SDW_UPDATE, pre->regs + IPU_PRE_CTRL_SET);
 }
 
+bool ipu_pre_update_pending(struct ipu_pre *pre)
+{
+	return !!(readl_relaxed(pre->regs + IPU_PRE_CTRL) &
+		  IPU_PRE_CTRL_SDW_UPDATE);
+}
+
 u32 ipu_pre_get_baddr(struct ipu_pre *pre)
 {
 	return (u32)pre->buffer_paddr;

drivers/gpu/ipu-v3/ipu-prv.h

@@ -272,6 +272,7 @@ void ipu_pre_configure(struct ipu_pre *pre, unsigned int width,
 		       unsigned int height, unsigned int stride, u32 format,
 		       uint64_t modifier, unsigned int bufaddr);
 void ipu_pre_update(struct ipu_pre *pre, unsigned int bufaddr);
+bool ipu_pre_update_pending(struct ipu_pre *pre);
 
 struct ipu_prg *ipu_prg_lookup_by_phandle(struct device *dev, const char *name,
 					  int ipu_id);