linux-kernel - Re: [PATCH 09/20] of/fdt: create common debugfs

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Date:	Fri, 04 Apr 2014 15:22:15 +0200
From:	Michal Simek <monstr@...str.eu>
To:	Rob Herring <robherring2@...il.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 09/20] of/fdt: create common debugfs

On 04/04/2014 03:00 PM, Rob Herring wrote:
> On Fri, Apr 4, 2014 at 7:16 AM, Michal Simek <monstr@...str.eu> wrote:
>> On 04/04/2014 12:16 AM, Rob Herring wrote:
>>> From: Rob Herring <robh@...nel.org>
>>>
>>> Both powerpc and microblaze have the same FDT blob in debugfs feature.
>>> Move this to common location and remove the powerpc and microblaze
>>> implementations. This feature could become more useful when FDT
>>> overlay support is added.
>>>
>>> This changes the path of the blob from "$arch/flat-device-tree" to
>>> "device-tree/flat-device-tree".
> 
> [snip]
> 
>>> -#if defined(CONFIG_DEBUG_FS) && defined(DEBUG)
>>> -static struct debugfs_blob_wrapper flat_dt_blob;
>>> -
>>> -static int __init export_flat_device_tree(void)
>>> -{
>>> -     struct dentry *d;
>>> -
>>> -     flat_dt_blob.data = initial_boot_params;
>>> -     flat_dt_blob.size = initial_boot_params->totalsize;
>>
>> As I see even microblaze version was buggy.
> 
> How so?

if you compare it with powerpc version here is missing
be to cpu conversion.

> 
>> ...
>>
>>> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
>>> index fa16a91..2085d47 100644
>>> --- a/drivers/of/fdt.c
>>> +++ b/drivers/of/fdt.c
>>> @@ -20,6 +20,7 @@
>>>  #include <linux/string.h>
>>>  #include <linux/errno.h>
>>>  #include <linux/slab.h>
>>> +#include <linux/debugfs.h>
>>>
>>>  #include <asm/setup.h>  /* for COMMAND_LINE_SIZE */
>>>  #ifdef CONFIG_PPC
>>> @@ -1084,4 +1085,27 @@ void __init unflatten_and_copy_device_tree(void)
>>>       unflatten_device_tree();
>>>  }
>>>
>>> +#if defined(CONFIG_DEBUG_FS) && defined(DEBUG)
>>> +static struct debugfs_blob_wrapper flat_dt_blob;
>>> +
>>> +static int __init of_flat_dt_debugfs_export_fdt(void)
>>> +{
>>> +     struct dentry *d = debugfs_create_dir("device-tree", NULL);
>>> +
>>> +     if (!d)
>>> +             return -ENOENT;
>>> +
>>> +     flat_dt_blob.data = initial_boot_params;
>>> +     flat_dt_blob.size = fdt_totalsize(initial_boot_params);
>>
>> Have you tried to compile this?
>>
>> From my tests fdt_totalsize is not available for target just for host
>> from libfdt.h
>>
>> drivers/of/fdt.c: In function 'of_flat_dt_debugfs_export_fdt':
>> drivers/of/fdt.c:957:2: error: implicit declaration of function 'fdt_totalsize' [-Werror=implicit-function-declaration]
> 
> Ah, it needs to be re-ordered after the libfdt conversion when
> libfdt.h gets added.

I just pick some of them not all of them and send email. :-(

Anyway I am testing it for microblaze and getting problem
caused by this patch:
commit 3d2ee8571ac0580d49c3f41fa28336289934900a
Author: Rob Herring <robh@...nel.org>
Date:   Wed Apr 2 15:10:14 2014 -0500

    of/fdt: Convert FDT functions to use libfdt

And reason is that in unflatten_dt_node()

pathp = fdt_get_name(blob, *poffset, &l);

is returning NULL
and here
	/* version 0x10 has a more compact unit name here instead of the full
	 * path. we accumulate the full path size using "fpsize", we'll rebuild
	 * it later. We detect this because the first character of the name is
	 * not '/'.
	 */
	if ((*pathp) != '/') {

code is trying to read it which is causing this kernel bug:
Oops: kernel access of bad area, sig: 11

It means fdt_next_node(is doing something wrong)

Any easy way how to debug it?

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
Maintainer of Linux kernel - Xilinx Zynq ARM architecture
Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform


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