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Re: [PATCH qemu v4] spapr: Kill SLOF

From: Alexey Kardashevskiy
Subject: Re: [PATCH qemu v4] spapr: Kill SLOF
Date: Fri, 10 Jan 2020 10:05:14 +1100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0

On 08/01/2020 17:18, Alexey Kardashevskiy wrote:
> The Petitboot bootloader is way more advanced than SLOF is ever going to
> be as Petitboot comes with the full-featured Linux kernel with all
> the drivers, and initramdisk with quite user friendly interface.
> The problem with ditching SLOF is that an unmodified pseries kernel can
> either start via:
> 1. kexec, this requires presence of RTAS and skips
> ibm,client-architecture-support entirely;
> 2. normal boot, this heavily relies on the OF1275 client interface to
> fetch the device tree and do early setup (claim memory).
> This adds a new bios-less mode to the pseries machine: "bios=on|off".
> When enabled, QEMU does not load SLOF and jumps to the kernel from
> "-kernel".
> The client interface is implemented exactly as RTAS - a 20 bytes blob,
> right next after the RTAS blob. The entry point is passed to the kernel
> via GPR5.
> This implements a handful of client interface methods just to get going.
> In particular, this implements the device tree fetching,
> ibm,client-architecture-support and instantiate-rtas.
> This implements changing FDT properties for RTAS (for vmlinux and zImage)
> and initramdisk location (for zImage). To make this work, this skips
> fdt_pack() when bios=off as not packing the blob leaves some room for
> appending.
> This assigns "phandles" to device tree nodes as there is no more SLOF
> and OF nodes addresses of which served as phandle values.
> This keeps predefined nodes (such as XICS/NVLINK/...) unchanged.
> phandles are regenerated at every FDT rebuild.
> This defines phandles for VIO devices to have phandle assigned to
> the default stdout device at the point when we write "/chosen/stdout"
> which an ihandle which the OS uses to write to the console.

And I do not really need to preallocate phandles for stdout as it is a
leftover from when I populated /chosen/stdout before populating VIO
nodes, now /chosen/stdout is added at the very end. Thanks,

> When bios=off, this adds "/chosen" every time QEMU builds a tree.
> This implements "claim" which the client (Linux) uses for memory
> allocation; this is also  used by QEMU for claiming kernel/initrd images,
> client interface entry point, RTAS and the initial stack.
> While at this, add a "kernel-addr" machine parameter to allow moving
> the kernel in memory. This is useful for debugging if the kernel is
> loaded at @0, although not necessary.
> This adds very basic instances support which are managed by a hashmap
> ihandle->phandle.
> Note that a 64bit PCI fix is required for Linux:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=df5be5be8735e


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