Subject: Re: Linux-3.14-rc2: Order of serial node compatibles in DTS files.

From: Sebastian Hesselbarth <[email-masked]>
Date: Wed, 12 Feb 2014 00:43:35 +0100

On 02/12/2014 12:38 AM, Stephen N Chivers wrote:
> Sebastian Hesselbarth <[email-masked]> wrote on
>> On 02/11/2014 11:33 PM, Kumar Gala wrote:
>>> On Feb 11, 2014, at 2:57 PM, Stephen N Chivers <[email-masked]> wrote:
>>>> I have been trial booting a 3.14-rc2 kernel for a 85xx platform
>>>> (dtbImage).
[...]
>>>>
>>>> of_serial f1004500.serial: Unknown serial port found, ignored.
>>>>
>>>> The serial nodes in boards dts file are specified as:
>>>>
>>>>          serial0: serial@4500 {
>>>>                          cell-index = <0>;
>>>>                          device_type = "serial";
>>>>                          compatible = "fsl,ns16550", "ns16550";
>>>>                          reg = <0x4500 0x100>;
>>>>                          clock-frequency = <0>;
>>>>                          interrupts = <0x2a 0x2>;
>>>>                          interrupt-parent = <&mpic>;
>>>>                  };
>>>
>>> Wondering if this caused the issue:
>>>
>>> commit 105353145eafb3ea919f5cdeb652a9d8f270228e
>>> Author: Sebastian Hesselbarth <[email-masked]>
>>> Date:   Tue Dec 3 14:52:00 2013 +0100
>>>
>>>       OF: base: match each node compatible against all given matches first
>>
[...]
>>
>> I don't think the missing compatible is causing it, but of_serial
>> provides a DT match for .type = "serial" just to fail later on
>> with the error seen above.
>>
>> The commit in question reorders of_match_device in a way that match
>> table order is not relevant anymore. This can cause it to match
>> .type = "serial" first here.
>>
>> Rather than touching the commit, I suggest to remove the problematic
>> .type = "serial" from the match table. It is of no use anyway.
> Deleting the "serial" line from the match table fixes the problem.
> I tested it for both orderings of compatible.

I revert my statement about removing anything from of_serial.c. Instead
we should try to prefer matches with compatibles over type/name without
compatibles. Something like the patch below (compile tested only)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index ff85450d5683..60da53b385ff 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -734,6 +734,7 @@ static
 const struct of_device_id *__of_match_node(const struct of_device_id *matches,
 					   const struct device_node *node)
 {
+	const struct of_device_id *m;
 	const char *cp;
 	int cplen, l;
 
@@ -742,15 +743,15 @@ const struct of_device_id *__of_match_node(const struct of_device_id *matches,
 
 	cp = __of_get_property(node, "compatible", &cplen);
 	do {
-		const struct of_device_id *m = matches;
+		m = matches;
 
 		/* Check against matches with current compatible string */
 		while (m->name[0] || m->type[0] || m->compatible[0]) {
 			int match = 1;
-			if (m->name[0])
+			if (m->name[0] && m->compatible[0])
 				match &= node->name
 					&& !strcmp(m->name, node->name);
-			if (m->type[0])
+			if (m->type[0] && m->compatible[0])
 				match &= node->type
 					&& !strcmp(m->type, node->type);
 			if (m->compatible[0])
@@ -770,6 +771,21 @@ const struct of_device_id *__of_match_node(const struct of_device_id *matches,
 		}
 	} while (cp && (cplen > 0));
 
+	/* Check against matches without compatible string */
+	m = matches;
+	while (m->name[0] || m->type[0]) {
+		int match = 1;
+		if (m->name[0])
+			match &= node->name
+				&& !strcmp(m->name, node->name);
+		if (m->type[0])
+			match &= node->type
+				&& !strcmp(m->type, node->type);
+		if (match)
+			return m;
+		m++;
+	}
+
 	return NULL;
 }