linux-kernel - [PATCH 2/2] mfd: madera: Wait for BOOT

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Message-ID: <20181001143357.28428-2-rf@opensource.cirrus.com>
Date:   Mon, 1 Oct 2018 15:33:57 +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 2/2] mfd: madera: Wait for BOOT_DONE before reading device ID

It isn't safe to read the device ID in SOFTWARE_RESET register
until the silicon boot sequence has completed. This patch
rearranges the code to wait for BOOT_DONE first.

If we don't have a GPIO to control hard reset we must issue
a soft reset to get the silicon into a known-good booted state
before reading the device ID.

Signed-off-by: Stuart Henderson <stuarth@...nsource.cirrus.com>
Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 drivers/mfd/madera-core.c | 33 +++++++++++++++------------------
 1 file changed, 15 insertions(+), 18 deletions(-)

diff --git a/drivers/mfd/madera-core.c b/drivers/mfd/madera-core.c
index 3ff9a0615658..b9d42edf96c9 100644
--- a/drivers/mfd/madera-core.c
+++ b/drivers/mfd/madera-core.c
@@ -454,10 +454,23 @@ int madera_dev_init(struct madera *madera)
 	regcache_cache_only(madera->regmap, false);
 	regcache_cache_only(madera->regmap_32bit, false);
 
+	/* If we don't have a reset GPIO use a soft reset */
+	if (!madera->pdata.reset) {
+		ret = madera_soft_reset(madera);
+		if (ret)
+			goto err_reset;
+	}
+
 	/*
-	 * Now we can power up and verify that this is a chip we know about
-	 * before we start doing any writes to its registers.
+	 * Must wait for internal boot sequence to complete before
+	 * reading the device ID
 	 */
+	ret = madera_wait_for_boot(madera);
+	if (ret) {
+		dev_err(madera->dev, "Device failed initial boot: %d\n", ret);
+		goto err_reset;
+	}
+
 	ret = regmap_read(madera->regmap, MADERA_SOFTWARE_RESET, &hwid);
 	if (ret) {
 		dev_err(dev, "Failed to read ID register: %d\n", ret);
@@ -519,22 +532,6 @@ int madera_dev_init(struct madera *madera)
 		goto err_reset;
 	}
 
-	/*
-	 * It looks like a device we support. If we don't have a hard reset
-	 * we can now attempt a soft reset.
-	 */
-	if (!madera->pdata.reset) {
-		ret = madera_soft_reset(madera);
-		if (ret)
-			goto err_reset;
-	}
-
-	ret = madera_wait_for_boot(madera);
-	if (ret) {
-		dev_err(madera->dev, "Device failed initial boot: %d\n", ret);
-		goto err_reset;
-	}
-
 	ret = regmap_read(madera->regmap, MADERA_HARDWARE_REVISION,
 			  &madera->rev);
 	if (ret) {
-- 
2.11.0