Re: [PATCH qemu v4] spapr: Kill SLOF

[David Gibson]

On Fri, Jan 10, 2020 at 11:51:32AM +1100, Alexey Kardashevskiy wrote:
> 
> 
> On 10/01/2020 10:32, Alexey Kardashevskiy wrote:
> > 
> > 
> > On 10/01/2020 10:05, Alexey Kardashevskiy wrote:
> >>
> >>
> >> 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,
> > 
> > 
> > Ah noo, I do, to implement "write" to the selected stdout as I need to
> > trace ihandle back to Object* and  object_resolve_path() does not know
> > about FDT path, it is /machine/peripheral/svty0 in QOM. The commit log
> > needs an update, or this needs a fix but I cannot think of a nicer one.
> > Thanks,
> 
> 
> I just might extend instances to do real instances, i.e. associate
> ihandle with phandle _and_ Object*, I just need a helper to find Object
> which matches what qdev_get_fw_dev_path() returns. Fun :)

If you only allow one instance per device, could you just make
ihandles == phandle | CONSTANT?

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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