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Date: Wed, 20 Mar 2024 13:05:57 -0700
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Subject: Re: [PATCH v4 1/2] of: create of_root if no dtb provided
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To: Rob Herring <robh+dt@kernel.org>
Cc: Stephen Boyd <sboyd@kernel.org>, Frank Rowand <frowand.list@gmail.com>,
 =?UTF-8?B?Q2zDqW1lbnQgTMOpZ2Vy?= <clement.leger@bootlin.com>,
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 Lizhi Hou <lizhi.hou@xilinx.com>, Allan Nielsen
 <allan.nielsen@microchip.com>, Horatiu Vultur
 <horatiu.vultur@microchip.com>, Steen Hegelund
 <steen.hegelund@microchip.com>,
 Thomas Petazzoni <thomas.petazzoni@bootlin.com>
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From: Guenter Roeck <linux@roeck-us.net>
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On 3/20/24 12:14, Rob Herring wrote:
> On Mon, Mar 18, 2024 at 4:31 PM Guenter Roeck <linux@roeck-us.net> wrote:
>>
>> On 3/18/24 12:26, Rob Herring wrote:
>>> +Stephen
>>>
>>> On Mon, Mar 18, 2024 at 12:09 PM Guenter Roeck <linux@roeck-us.net> wrote:
>>>>
>>>> Hi,
>>>>
>>>> On Fri, Mar 17, 2023 at 12:34:14AM -0500, Frank Rowand wrote:
>>>>> When enabling CONFIG_OF on a platform where of_root is not populated by
>>>>> firmware, we end up without a root node. In order to apply overlays and
>>>>> create subnodes of the root node, we need one. Create this root node
>>>>> by unflattening an empty builtin dtb.
>>>>>
>>>>> If firmware provides a flattened device tree (FDT) then the FDT is
>>>>> unflattened via setup_arch().  Otherwise setup_of(), which is called
>>>>> immediately after setup_arch(), will create the default root node
>>>>> if it does not exist.
>>>>>
>>>>> Signed-off-by: Frank Rowand <frowand.list@gmail.com>
>>>>
>>>> This patch results in a crash on nios2.
>>>
>>> This patch was never applied. I assume you meant a later version of it
>>> that did get applied.
>>>
>>>>
>>>> Building nios2:10m50-ghrd:10m50_defconfig:10m50_devboard.dts ... running ...R failed (crashed)
>>>
>>> Booting with DT?
>>>
>>>> ------------
>>>> qemu log:
>>>> earlycon: uart8250 at MMIO32 0x18001600 (options '')
>>>> printk: legacy bootconsole [uart8250] enabled
>>>> Linux version 6.8.0-11409-gf6cef5f8c37f (groeck@desktop) (nios2-linux-gcc (GCC) 11.4.0, GNU ld (GNU Binutils) 2.40) #1 Sun Mar 17 23:38:59 PDT 2024
>>>> Kernel panic - not syncing: early_init_dt_alloc_memory_arch: Failed to allocate 72 bytes align=0x40
>>>> ---[ end Kernel panic - not syncing: early_init_dt_alloc_memory_arch: Failed to allocate 72 bytes align=0x40 ]---
>>>
>>> nios2 looks utterly broken to me. This change should be a nop unless
>>> initial_boot_params is NULL. It looks like it is possible for r6 (dtb
>>> address) to be 0 depending on kconfig options, but that would have
>>> skipped copying and unflattening which would then panic in
>>> setup_cpuinfo(). If initial_boot_params is not NULL, then the same
>>> early_init_dt_alloc_memory_arch() calls should fail when copying the
>>> DT. So I don't see how nios2 booting with DT ever worked.
>>>
>>
>> For nios2, in early_init_devtree():
>>
>> void __init early_init_devtree(void *params)
>> {
>>           __be32 *dtb = (u32 *)__dtb_start;
>>          ...
>>           if (be32_to_cpu((__be32) *dtb) == OF_DT_HEADER)
>>                   params = (void *)__dtb_start;
>>
>> That worked fine until this patch. Starting with this patch, __dtb_start
>> always points to a valid empty devicetree blob, which overrides the
>> devicetree blob passed to early_init_devtree(). This causes the problem.
> 
> With an external DTB, it doesn't boot with or without this patch. It
> just dies in different spots. Before it just skipped any memory

No, that is incorrect. Up to this patch it booted just fine with an
external dtb using the "-initrd" command line argument, and I explained
to you above why this is the case.

I guess you are saying I should stop boot testing nios2. I'll do just that.
Saves me resources and avoids discussions like this.

Guenter