linux-kernel - [PATCH v2 2/2] mfd: madera: Wait for BOOT

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Date:   Tue, 2 Oct 2018 11:41:34 +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 2/2] mfd: madera: Wait for BOOT_DONE before reading device ID

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

If we don't have a hard reset line we want to defer writing a
soft reset command until we have identified the silicon as
something we recognize. As the BOOT_DONE bit is sticky it is
safe to wait for it without issuing a soft reset first, because
the most recent power-up will have caused a boot sequence and
set the bit. Note that the boot sequence is not the same as a
reset so we still have to soft reset to get the codec into a
known state.

Signed-off-by: Stuart Henderson <stuarth@...nsource.cirrus.com>
Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 drivers/mfd/madera-core.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/mfd/madera-core.c b/drivers/mfd/madera-core.c
index 1dedfe68a3dc..e114ca5e6c3f 100644
--- a/drivers/mfd/madera-core.c
+++ b/drivers/mfd/madera-core.c
@@ -455,10 +455,13 @@ int madera_dev_init(struct madera *madera)
 	regcache_cache_only(madera->regmap, false);
 	regcache_cache_only(madera->regmap_32bit, false);
 
-	/*
-	 * Now we can power up and verify that this is a chip we know about
-	 * before we start doing any writes to its registers.
-	 */
+	/* BOOT_DONE must be set before we can read 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);
@@ -528,12 +531,13 @@ int madera_dev_init(struct madera *madera)
 		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 = madera_wait_for_boot(madera);
+		if (ret) {
+			dev_err(madera->dev, "Device failed initial soft reboot: %d\n",
+				ret);
+			goto err_reset;
+		}
 	}
 
 	ret = regmap_read(madera->regmap, MADERA_HARDWARE_REVISION,
-- 
2.11.0