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Re: [Qemu-arm] [Qemu-devel] [PATCH v3 07/10] hw/arm/virt: Introduce opt-

From: Laszlo Ersek
Subject: Re: [Qemu-arm] [Qemu-devel] [PATCH v3 07/10] hw/arm/virt: Introduce opt-in feature "fdt"
Date: Tue, 2 Apr 2019 17:56:00 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 04/02/19 17:52, Laszlo Ersek wrote:
> On 04/02/19 17:42, Auger Eric wrote:

>>>>> The firmware does consume DT:
>>>>> - If you start QEMU *with* "-no-acpi", then the DT is both consumed by
>>>>> the firmware (for its own information needs), and passed on to the OS.
>>>>> - If you start QEMU *without* "-no-acpi" (the default), then the DT is
>>>>> consumed only by the firmware (for its own information needs), and the
>>>>> DT is hidden from the OS. The OS gets only the ACPI content
>>>>> (processed/prepared as described above).
>> I am confused by the above statement actually. In the above case what
>> does happen if you pass the acpi=off in the kernel boot parameters?
> If you launch QEMU with "-no-acpi" and you pass "acpi=off" to the guest
> kernel, then the kernel will not boot successfully, as it will not get
> DT from the firmware, and it will ignore the ACPI tables that it does
> get from the firmware.

Sorry, I ended up answering "what happens when you run QEMU *without*
-no-acpi and pass acpi=off to the guest kernel".

To explain what happens when you boot *with* -no-acpi: in that case,
"acpi=off" doesn't matter, since the guest kernel doesn't get ACPI
tables anyway. The kernel will go for DT.


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