diff --git a/drivers/mfd/macsmc.c b/drivers/mfd/macsmc.c
index ac9d821bf865c..e88af94489c05 100644
--- a/drivers/mfd/macsmc.c
+++ b/drivers/mfd/macsmc.c
@@ -13,6 +13,7 @@
 #include <linux/io.h>
 #include <linux/ioport.h>
 #include <linux/iopoll.h>
+#include <linux/ktime.h>
 #include <linux/math.h>
 #include <linux/mfd/core.h>
 #include <linux/mfd/macsmc.h>
@@ -46,6 +47,8 @@
 #define SMC_RESULT			SMC_MSG
 
 #define SMC_TIMEOUT_MS		500
+/* Restart and power-off go through atomic writes; give the SMC time. */
+#define SMC_ATOMIC_TIMEOUT_MS	5000
 
 static const struct mfd_cell apple_smc_devs[] = {
 	MFD_CELL_NAME("macsmc-input"),
@@ -283,6 +286,8 @@ int apple_smc_write_atomic(struct apple_smc *smc, smc_key key, const void *buf,
 	u8 result;
 	int ret, poll_ret;
 	u64 msg;
+	ktime_t t0;
+	s64 us;
 
 	if (size > SMC_MAX_SIZE || size == 0)
 		return -EINVAL;
@@ -296,9 +301,17 @@ int apple_smc_write_atomic(struct apple_smc *smc, smc_key key, const void *buf,
 	 * release its SRAM. Its late reply does: take it if it has arrived.
 	 */
 	if (smc->atomic_pending) {
-		ret = apple_rtkit_poll(smc->rtk);
-		if (ret < 0 || smc->atomic_pending)
+		/* Wait for the earlier command's late reply instead of giving up. */
+		ret = read_poll_timeout_atomic(apple_rtkit_poll, poll_ret,
+					       poll_ret < 0 || !smc->atomic_pending,
+					       100, SMC_ATOMIC_TIMEOUT_MS * USEC_PER_MSEC,
+					       false, smc->rtk);
+		if (poll_ret < 0 || smc->atomic_pending) {
+			dev_err(smc->dev, "atomic: earlier command still pending (%d/%d)\n",
+				ret, poll_ret);
 			return -EBUSY;
+		}
+		dev_warn(smc->dev, "atomic: earlier command's reply arrived late\n");
 	}
 
 	memcpy_toio(smc->shmem.iomem, buf, size);
@@ -317,10 +330,15 @@ int apple_smc_write_atomic(struct apple_smc *smc, smc_key key, const void *buf,
 		return ret;
 	}
 
+	t0 = ktime_get();
 	ret = read_poll_timeout_atomic(apple_rtkit_poll, poll_ret,
 				       poll_ret < 0 || !smc->atomic_pending,
-				       100, SMC_TIMEOUT_MS * USEC_PER_MSEC,
+				       100, SMC_ATOMIC_TIMEOUT_MS * USEC_PER_MSEC,
 				       false, smc->rtk);
+	us = ktime_us_delta(ktime_get(), t0);
+	if (us > 100 * USEC_PER_MSEC || ret < 0 || smc->atomic_pending)
+		dev_warn(smc->dev, "atomic: key %p4ch reply after %lld us (ret %d)\n",
+			 &key, us, ret);
 	if (poll_ret < 0) {
 		dev_err(smc->dev, "RTKit poll failed (%llx)", msg);
 		return poll_ret;