clk: renesas: mstp: Convert to readl_poll_timeout_atomic()

Use readl_poll_timeout_atomic() instead of open-coding the same
operation.

As typically no retries are needed, 10 µs is a suitable timeout value.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/bce7d0bdd80c800aa150f1868b610b7d94f4cc66.1685692810.git.geert+renesas@glider.be

Author: geertu

drivers/clk/renesas/clk-mstp.c

@@ -14,6 +14,7 @@
 #include <linux/clk/renesas.h>
 #include <linux/device.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
 #include <linux/pm_clock.h>
@@ -78,8 +79,8 @@ static int cpg_mstp_clock_endisable(struct clk_hw *hw, bool enable)
 	struct mstp_clock_group *group = clock->group;
 	u32 bitmask = BIT(clock->bit_index);
 	unsigned long flags;
-	unsigned int i;
 	u32 value;
+	int ret;
 
 	spin_lock_irqsave(&group->lock, flags);
 
@@ -101,19 +102,14 @@ static int cpg_mstp_clock_endisable(struct clk_hw *hw, bool enable)
 	if (!enable || !group->mstpsr)
 		return 0;
 
-	for (i = 1000; i > 0; --i) {
-		if (!(cpg_mstp_read(group, group->mstpsr) & bitmask))
-			break;
-		cpu_relax();
-	}
-
-	if (!i) {
+	/* group->width_8bit is always false if group->mstpsr is present */
+	ret = readl_poll_timeout_atomic(group->mstpsr, value,
+					!(value & bitmask), 0, 10);
+	if (ret)
 		pr_err("%s: failed to enable %p[%d]\n", __func__,
 		       group->smstpcr, clock->bit_index);
-		return -ETIMEDOUT;
-	}
 
-	return 0;
+	return ret;
 }
 
 static int cpg_mstp_clock_enable(struct clk_hw *hw)