linux-kernel - [PATCH v2 1/2] mfd: madera: Increase wait time for silicon reset

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Message-ID: <20181002104134.29003-1-rf@opensource.cirrus.com>
Date:   Tue, 2 Oct 2018 11:41:33 +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 1/2] mfd: madera: Increase wait time for silicon reset

Based on latest silicon validation, we should allow at least
2 milliseconds after DCVDD enable or hard reset before trying
to communicate with the silicon.

Previously the delay was done as a side-effect of
madera_disable_hard_reset(). As we also need this delay when
enabling DCVDD (with or without hard reset) it is better for it
to be obvious where it happens in every power-up sequence rather
than hidden within another call in some cases. So it has been
moved out into a separate function call.

Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 drivers/mfd/madera-core.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/mfd/madera-core.c b/drivers/mfd/madera-core.c
index 440030cecbbd..1dedfe68a3dc 100644
--- a/drivers/mfd/madera-core.c
+++ b/drivers/mfd/madera-core.c
@@ -135,6 +135,15 @@ EXPORT_SYMBOL_GPL(madera_name_from_type);
 #define MADERA_BOOT_POLL_INTERVAL_USEC		5000
 #define MADERA_BOOT_POLL_TIMEOUT_USEC		25000
 
+static void madera_por_delay(void)
+{
+	/*
+	 * Delay after DCVDD enable or hard reset to allow for silicon POR
+	 * (power-on reset).
+	 */
+	usleep_range(2000, 3000);
+}
+
 static int madera_wait_for_boot(struct madera *madera)
 {
 	ktime_t timeout;
@@ -209,7 +218,6 @@ static void madera_disable_hard_reset(struct madera *madera)
 		return;
 
 	gpiod_set_raw_value_cansleep(madera->pdata.reset, 1);
-	usleep_range(1000, 2000);
 }
 
 static int __maybe_unused madera_runtime_resume(struct device *dev)
@@ -225,6 +233,8 @@ static int __maybe_unused madera_runtime_resume(struct device *dev)
 		return ret;
 	}
 
+	madera_por_delay();
+
 	regcache_cache_only(madera->regmap, false);
 	regcache_cache_only(madera->regmap_32bit, false);
 
@@ -440,6 +450,7 @@ int madera_dev_init(struct madera *madera)
 	}
 
 	madera_disable_hard_reset(madera);
+	madera_por_delay();
 
 	regcache_cache_only(madera->regmap, false);
 	regcache_cache_only(madera->regmap_32bit, false);
-- 
2.11.0