From f18fbc09223234947b22434b5fa7fd684d17f448 Mon Sep 17 00:00:00 2001
From: John Klug <john.klug@multitech.com>
Date: Thu, 17 Feb 2022 18:23:05 -0600
Subject: Unload the driver if platform_driver register fails, add README to
 explain the history of MTS-IO

---
 README              | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 configure.ac        |  2 +-
 io-module/mts-io.c  | 14 ++++++-----
 io-module/version.h |  2 +-
 4 files changed, 77 insertions(+), 8 deletions(-)

diff --git a/README b/README
index d4a3df6..980ea75 100644
--- a/README
+++ b/README
@@ -15,3 +15,70 @@ the on-board EE-PROM.
 dev_dbg can be turned on when loading the
 mts-io driver.  See debug/README and
 debug/etc/modprobe.d/mts-io.conf
+
+HISTORY:
+Before the 4.9 kernel, mLinux used a patch
+of the GPIO library to add pull up and pull
+down capability to the GPIO flags.
+
+This patch did not easily fit with
+newer kernels.  So instead, the pull
+up and pull down code was moved todata
+device tree and AT91Pincontrol
+(for Atmel processors)
+from the mts-io driver.
+
+When the mts-io module was loaded, the
+device tree was scanned, and the
+pinctrl elements in device tree
+associated with the mts-io driver
+were loaded.
+
+Before the 4.9 version of the mts-io
+driver, on initial load, the probe
+function was executed.  The probe
+function in the device tree model
+of the kernel causes a search
+of the device tree and when
+an element is found with the appropriate
+compatible property, that part of the device tree
+is loaded.  This caused the attached
+pinctrl sections to be read and the pins
+configured.
+
+Because the kernel doc suggests adding
+a number at the end of a node name, mts-io-0
+was chosen.
+
+Because the mts-io driver had always allocated
+its own platform, it already had a
+platform called mts-io.  Because of this, we
+did a platform_driver_register, followed
+immediately by a platform_driver_unregister.
+This allowed us to set up the pins using
+device tree and allowed us to keep all
+the old code that created and used the
+platform driver with a minimum of changes.
+The device tree used mts-io-0 for the 
+mts-io driver node which became
+/sys/devices/platform/mts-io-0.  The
+mts-io driver continues to use
+/sys/devices/platform/mts-io.
+
+Now at the 4.9 mts-io version level,
+an attempt is made to move towards using
+the gpio connection-id's from the
+newer gpiod library.  These connection-ids
+are referred to as "names" in device tree
+documentation.  It is no longer possible
+to free the platform loaded by 
+platform_driver_register, because
+we need to use these device tree
+entries later in the driver.
+
+GPIO pins are then be attached through the GPIO
+descriptor found by making a call to
+kernel functions like devm_gpiod_get_optional(),
+which has a connection-ID as its second
+parameter.
+
diff --git a/configure.ac b/configure.ac
index 470aeac..d65d2a5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,4 +1,4 @@
-AC_INIT([mts-io], [4.9.0])
+AC_INIT([mts-io], [4.9.1])
 AC_CONFIG_SRCDIR([util/mts_util_lora2_reset.c])
 AM_INIT_AUTOMAKE
 AM_CONFIG_HEADER([config.h])
diff --git a/io-module/mts-io.c b/io-module/mts-io.c
index db736f9..d65c7ea 100644
--- a/io-module/mts-io.c
+++ b/io-module/mts-io.c
@@ -1347,12 +1347,7 @@ static int __init mts_io_init(void)
 	log_info("init: " DRIVER_VERSION);
 
 	/* We do a platform_driver_register to do a probe
-	 * of device tree and set the pinctrl.  We then
-	 * unregister to remove
-	 * the probe function.  If we don't remove the
-	 * probe function, we will do a 2nd probe in
-	 * platform_device_add, which will result in a
-	 * stack trace in the log. */
+	 * of device tree and set the pinctrl/gpio settings. */
 	ret = platform_driver_register(&mts_io_driver);
 	if (ret) {
 		printk(KERN_ERR "mts-io: probe failed: %d\n", ret);
@@ -1360,6 +1355,13 @@ static int __init mts_io_init(void)
 		return ret;
 	}
 
+	/* Without a platform device our EEPROM load will
+         * not work, and we cannot continue. */
+        if (mts_io_platform_device == NULL) {
+                pr_err("mts-io: probe failed, possible bad device tree\n");
+                return -ENODEV;
+        }
+
 	/* request_firmware() requires a device, so call after device allocated */
 	ret = mts_id_eeprom_load();
 
diff --git a/io-module/version.h b/io-module/version.h
index a97e7df..b72c4b0 100644
--- a/io-module/version.h
+++ b/io-module/version.h
@@ -1,7 +1,7 @@
 #ifndef __VERSION_H
 #define __VERSION_H
 
-#define DRIVER_VERSION  "v4.9.0"
+#define DRIVER_VERSION  "v4.9.1"
 #define DRIVER_AUTHOR   "Multitech Systems"
 #define DRIVER_DESC "MTS-IO Controller"
 #define DRIVER_NAME "mts-io"
-- 
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