clk: renesas: mstp: ensure register writes complete

When there is no status bit, it is possible for the clock enable/disable
operation to have not completed by the time the driver code resumes
execution. This is due to the fact that write operations are sometimes
queued and delayed internally. Doing a read ensures the write operations
has completed.

Fixes: b6face404f ("ARM: shmobile: r7s72100: add essential clock nodes to dtsi")
Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

drivers/clk/renesas/clk-mstp.c

@@ -91,6 +91,12 @@ static int cpg_mstp_clock_endisable(struct clk_hw *hw, bool enable)
 		value |= bitmask;
 	cpg_mstp_write(group, value, group->smstpcr);
 
+	if (!group->mstpsr) {
+		/* dummy read to ensure write has completed */
+		cpg_mstp_read(group, group->smstpcr);
+		barrier_data(group->smstpcr);
+	}
+
 	spin_unlock_irqrestore(&group->lock, flags);
 
 	if (!enable || !group->mstpsr)