Re: [PATCH v4 1/2] of: create of_root if no dtb provided

From: Guenter Roeck <linux@roeck-us.net>
To: Rob Herring <robh+dt@kernel.org>, Stephen Boyd <sboyd@kernel.org>
Cc: "Frank Rowand" <frowand.list@gmail.com>,
	"Clément Léger" <clement.leger@bootlin.com>,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	"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>
Subject: Re: [PATCH v4 1/2] of: create of_root if no dtb provided
Date: Mon, 18 Mar 2024 13:47:11 -0700	[thread overview]
Message-ID: <d259663b-8713-4c7a-8872-ea775882891d@roeck-us.net> (raw)
In-Reply-To: <CAL_JsqKsF53v7d7uZ3XT4kPFy-2FBWHfvKNSFdTx2oZhmSZkDA@mail.gmail.com>

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.
> 

It is the patch in the link that was provided with the patch. What else
should we use as reference ? FWIW, I did look for a more recent version,
but I must have missed it. My bad.

>>
>> Building nios2:10m50-ghrd:10m50_defconfig:10m50_devboard.dts ... running ...R failed (crashed)
> 
> Booting with DT?
> 

Yes, with arch/nios2/boot/dts/10m50_devboard.dtb.

>> ------------
>> 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.
> 

All I can say that it did work with devicetree until this patch was
applied. It doesn't boot without it. I tried without devicetree file
after reverting this patch. That results in

Kernel panic - not syncing: setup_cpuinfo: No CPU found in devicetree!

Guenter