[U-Boot] [PATCH v2 24/29] riscv: store device tree passed by prior boot stage in environment

[Alexander Graf]

On 30.10.18 14:44, Auer, Lukas wrote:
> On Tue, 2018-10-30 at 14:19 +0100, Alexander Graf wrote:
>>
>> On 30.10.18 13:55, Lukas Auer wrote:
>>> The device tree passed by the prior boot stage can be used to boot
>>> Linux. Store it as environment variable "prior_stage_dtb", so that
>>> it
>>> can be used as part of the boot command.
>>>
>>> Signed-off-by: Lukas Auer <lukas.auer at aisec.fraunhofer.de>
>>> ---
>>>
>>> Changes in v2:
>>> - New patch
>>>
>>>  arch/Kconfig                          | 1 +
>>>  arch/riscv/cpu/cpu.c                  | 7 +++++++
>>>  arch/riscv/include/asm/u-boot-riscv.h | 1 +
>>>  3 files changed, 9 insertions(+)
>>>
>>> diff --git a/arch/Kconfig b/arch/Kconfig
>>> index 9fdd2f7e66..883e4a9308 100644
>>> --- a/arch/Kconfig
>>> +++ b/arch/Kconfig
>>> @@ -74,6 +74,7 @@ config RISCV
>>>  	imply MTD
>>>  	imply TIMER
>>>  	imply CMD_DM
>>> +	imply ARCH_MISC_INIT
>>>  
>>>  config SANDBOX
>>>  	bool "Sandbox"
>>> diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
>>> index d9f820c44c..e06a8c6bab 100644
>>> --- a/arch/riscv/cpu/cpu.c
>>> +++ b/arch/riscv/cpu/cpu.c
>>> @@ -53,3 +53,10 @@ int print_cpuinfo(void)
>>>  
>>>  	return 0;
>>>  }
>>> +
>>> +int arch_misc_init(void)
>>> +{
>>> +	env_set_hex("prior_stage_dtb", prior_stage_fdt_address);
>>
>> Please reuse one of the many other variable names we have for this
>> already, such as "fdtaddr".
>>
> 
> I will change the variable name.
> 
>> One thing I would always recommend is that if you have a prior stage
>> DT
>> passed on to U-Boot is that U-Boot makes use of that
>> (CONFIG_OF_BOARD).
>> That again means that the DT is already available in $fdtcontroladdr
>> and
>> there is very little use for yet another env variable.
>>
>>
>> Alex
>>
> 
> We are actually using the device tree passed to U-Boot (using
> CONFIG_OF_PRIOR_STAGE). The reason I'm adding the device tree address
> to the environment is so that it can be used to boot Linux. RISC-V
> Linux does not include any device trees, they are instead stored
> directly on the SoC (though this might change). This is therefore
> important to have and this is the best way I could think of, of
> implementing it.

Oh, I'm in 100% agreement that this is the right choice. I'm just
surprised we have 2 Kconfig options to basically do the same thing. The
RPi uses CONFIG_OF_BOARD while newer BCM chips seem to use
CONFIG_PRIOR_STAGE. It's slightly counterintuitive :).

What I was saying is that U-Boot should be a consumer of said "platform
device tree" and thus exposes it as $fdtcontroladdr into the
environment. So instead of

  # bootefi $kernel_addr_r $fdtaddr

you could as well just use

  # bootefi $kernel_addr_r $fdtcontroladdr

which the distro scripts automatically do for you, so you already have
what you asked for :).


Alex