linux-kernel - [PATCH v2] mfd: madera: Don't use regmap_read_poll_timeout to poll for BOOT

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Date:   Mon, 27 Aug 2018 14:51:15 +0100
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     <lee.jones@...aro.org>
CC:     <patches@...nsource.cirrus.com>, <linux-kernel@...r.kernel.org>,
        "Richard Fitzgerald" <rf@...nsource.cirrus.com>
Subject: [PATCH v2] mfd: madera: Don't use regmap_read_poll_timeout to poll for BOOT_DONE

While polling for BOOT_DONE the chip could NAK a read because it is
still booting, which would terminate the regmap_read_poll_timeout()
with an error.

Instead implement a polling loop that ignores read errors so we
always poll until the chip signals boot or the loop times out.

Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 drivers/mfd/madera-core.c | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/drivers/mfd/madera-core.c b/drivers/mfd/madera-core.c
index 8cfea969b060..440030cecbbd 100644
--- a/drivers/mfd/madera-core.c
+++ b/drivers/mfd/madera-core.c
@@ -132,32 +132,39 @@ const char *madera_name_from_type(enum madera_type type)
 }
 EXPORT_SYMBOL_GPL(madera_name_from_type);
 
-#define MADERA_BOOT_POLL_MAX_INTERVAL_US  5000
-#define MADERA_BOOT_POLL_TIMEOUT_US	 25000
+#define MADERA_BOOT_POLL_INTERVAL_USEC		5000
+#define MADERA_BOOT_POLL_TIMEOUT_USEC		25000
 
 static int madera_wait_for_boot(struct madera *madera)
 {
+	ktime_t timeout;
 	unsigned int val;
-	int ret;
+	int ret = 0;
 
 	/*
 	 * We can't use an interrupt as we need to runtime resume to do so,
 	 * so we poll the status bit. This won't race with the interrupt
 	 * handler because it will be blocked on runtime resume.
+	 * The chip could NAK a read request while it is booting so ignore
+	 * errors from regmap_read.
 	 */
-	ret = regmap_read_poll_timeout(madera->regmap,
-				       MADERA_IRQ1_RAW_STATUS_1,
-				       val,
-				       (val & MADERA_BOOT_DONE_STS1),
-				       MADERA_BOOT_POLL_MAX_INTERVAL_US,
-				       MADERA_BOOT_POLL_TIMEOUT_US);
-
-	if (ret)
-		dev_err(madera->dev, "Polling BOOT_DONE_STS failed: %d\n", ret);
+	timeout = ktime_add_us(ktime_get(), MADERA_BOOT_POLL_TIMEOUT_USEC);
+	regmap_read(madera->regmap, MADERA_IRQ1_RAW_STATUS_1, &val);
+	while (!(val & MADERA_BOOT_DONE_STS1) &&
+	       !ktime_after(ktime_get(), timeout)) {
+		usleep_range(MADERA_BOOT_POLL_INTERVAL_USEC / 2,
+			     MADERA_BOOT_POLL_INTERVAL_USEC);
+		regmap_read(madera->regmap, MADERA_IRQ1_RAW_STATUS_1, &val);
+	};
+
+	if (!(val & MADERA_BOOT_DONE_STS1)) {
+		dev_err(madera->dev, "Polling BOOT_DONE_STS timed out\n");
+		ret = -ETIMEDOUT;
+	}
 
 	/*
 	 * BOOT_DONE defaults to unmasked on boot so we must ack it.
-	 * Do this unconditionally to avoid interrupt storms.
+	 * Do this even after a timeout to avoid interrupt storms.
 	 */
 	regmap_write(madera->regmap, MADERA_IRQ1_STATUS_1,
 		     MADERA_BOOT_DONE_EINT1);
-- 
2.11.0