We support the fw_cfg device on more architectures and machines that
we let on about in the documentation.  Luckily most of the new ones
(notably riscv and loongarch) have followed the straightforward layout
that the Arm virt board picked. Allowing every machine type to have
its own special-snowflake register layout has no particular benefits
and tends to result in guest OSes accumulating ifdef ladders to deal
with all the unnecessary variation.
    
This patchset:
 * updates the docs to present the arm/riscv/loongarch memory
   mapped layout as the "standard" layout to be used by all
   new architectures/machines in future
 * adds the layouts used by various existing boards that we
   didn't document (PA-RISC, SPARC, PPC and MIPS)
 * tightens up fw_cfg_init_mem_dma() and fw_cfg_init_io_dma()
   functions so that they don't provide flexibility to the
   caller to pick their own weird new layout. None of the
   callers were using this flexibility, so it's better to
   have fw_cfg_init_mem_dma() give the "standard MMIO" layout
   and fw_cfg_init_io_dma() give the x86 ioport layout.

thanks
-- PMM

Peter Maydell (5):
  docs/specs/fw_cfg: Document all architecture register layouts
  hw/nvram/fw_cfg: Enforce standard layout for fw_cfg_init_mem_dma()
  hw/nvram/fw_cfg: Enforce standard layout for x86 fw_cfg I/O ports
  hw/nvram/fw_cfg: Remove support for I/O port fw_cfg without DMA
  hw/nvram/fw_cfg: Document fw_cfg_init_mem_nodma()

 docs/specs/fw_cfg.rst     | 28 ++++++++++++++++---
 hw/arm/virt.c             |  2 +-
 hw/i386/fw_cfg.c          |  3 +-
 hw/i386/microvm.c         |  3 +-
 hw/i386/pc.c              |  3 +-
 hw/loongarch/fw_cfg.c     |  3 +-
 hw/nvram/fw_cfg.c         | 22 ++++++---------
 hw/riscv/virt.c           |  3 +-
 include/hw/nvram/fw_cfg.h | 58 +++++++++++++++++++++++++++++++++++----
 9 files changed, 92 insertions(+), 33 deletions(-)

-- 
2.43.0

These have all now been reviewed. Since fw_cfg is marked as
Orphaned in MAINTAINERS, I'm going to take the series via
target-arm.next. Let me know if anybody would prefer something else.

thanks
-- PMM

On Fri, 29 May 2026 at 18:46, Peter Maydell <peter.maydell@linaro.org> wrote:
>
> We support the fw_cfg device on more architectures and machines that
> we let on about in the documentation.  Luckily most of the new ones
> (notably riscv and loongarch) have followed the straightforward layout
> that the Arm virt board picked. Allowing every machine type to have
> its own special-snowflake register layout has no particular benefits
> and tends to result in guest OSes accumulating ifdef ladders to deal
> with all the unnecessary variation.
>
> This patchset:
>  * updates the docs to present the arm/riscv/loongarch memory
>    mapped layout as the "standard" layout to be used by all
>    new architectures/machines in future
>  * adds the layouts used by various existing boards that we
>    didn't document (PA-RISC, SPARC, PPC and MIPS)
>  * tightens up fw_cfg_init_mem_dma() and fw_cfg_init_io_dma()
>    functions so that they don't provide flexibility to the
>    caller to pick their own weird new layout. None of the
>    callers were using this flexibility, so it's better to
>    have fw_cfg_init_mem_dma() give the "standard MMIO" layout
>    and fw_cfg_init_io_dma() give the x86 ioport layout.
>
> thanks
> -- PMM
>
> Peter Maydell (5):
>   docs/specs/fw_cfg: Document all architecture register layouts
>   hw/nvram/fw_cfg: Enforce standard layout for fw_cfg_init_mem_dma()
>   hw/nvram/fw_cfg: Enforce standard layout for x86 fw_cfg I/O ports
>   hw/nvram/fw_cfg: Remove support for I/O port fw_cfg without DMA
>   hw/nvram/fw_cfg: Document fw_cfg_init_mem_nodma()
>
>  docs/specs/fw_cfg.rst     | 28 ++++++++++++++++---
>  hw/arm/virt.c             |  2 +-
>  hw/i386/fw_cfg.c          |  3 +-
>  hw/i386/microvm.c         |  3 +-
>  hw/i386/pc.c              |  3 +-
>  hw/loongarch/fw_cfg.c     |  3 +-
>  hw/nvram/fw_cfg.c         | 22 ++++++---------
>  hw/riscv/virt.c           |  3 +-
>  include/hw/nvram/fw_cfg.h | 58 +++++++++++++++++++++++++++++++++++----
>  9 files changed, 92 insertions(+), 33 deletions(-)

On Fri, Jul 03, 2026 at 10:41:32AM +0100, Peter Maydell wrote:
> These have all now been reviewed. Since fw_cfg is marked as
> Orphaned in MAINTAINERS,

I don't think fw cfg is good as orphaned.
Any takers? If not I guess I will have to add myself there.

> I'm going to take the series via
> target-arm.next. Let me know if anybody would prefer something else.
> 
> thanks
> -- PMM

Pls go ahead:
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>


> On Fri, 29 May 2026 at 18:46, Peter Maydell <peter.maydell@linaro.org> wrote:
> >
> > We support the fw_cfg device on more architectures and machines that
> > we let on about in the documentation.  Luckily most of the new ones
> > (notably riscv and loongarch) have followed the straightforward layout
> > that the Arm virt board picked. Allowing every machine type to have
> > its own special-snowflake register layout has no particular benefits
> > and tends to result in guest OSes accumulating ifdef ladders to deal
> > with all the unnecessary variation.
> >
> > This patchset:
> >  * updates the docs to present the arm/riscv/loongarch memory
> >    mapped layout as the "standard" layout to be used by all
> >    new architectures/machines in future
> >  * adds the layouts used by various existing boards that we
> >    didn't document (PA-RISC, SPARC, PPC and MIPS)
> >  * tightens up fw_cfg_init_mem_dma() and fw_cfg_init_io_dma()
> >    functions so that they don't provide flexibility to the
> >    caller to pick their own weird new layout. None of the
> >    callers were using this flexibility, so it's better to
> >    have fw_cfg_init_mem_dma() give the "standard MMIO" layout
> >    and fw_cfg_init_io_dma() give the x86 ioport layout.
> >
> > thanks
> > -- PMM
> >
> > Peter Maydell (5):
> >   docs/specs/fw_cfg: Document all architecture register layouts
> >   hw/nvram/fw_cfg: Enforce standard layout for fw_cfg_init_mem_dma()
> >   hw/nvram/fw_cfg: Enforce standard layout for x86 fw_cfg I/O ports
> >   hw/nvram/fw_cfg: Remove support for I/O port fw_cfg without DMA
> >   hw/nvram/fw_cfg: Document fw_cfg_init_mem_nodma()
> >
> >  docs/specs/fw_cfg.rst     | 28 ++++++++++++++++---
> >  hw/arm/virt.c             |  2 +-
> >  hw/i386/fw_cfg.c          |  3 +-
> >  hw/i386/microvm.c         |  3 +-
> >  hw/i386/pc.c              |  3 +-
> >  hw/loongarch/fw_cfg.c     |  3 +-
> >  hw/nvram/fw_cfg.c         | 22 ++++++---------
> >  hw/riscv/virt.c           |  3 +-
> >  include/hw/nvram/fw_cfg.h | 58 +++++++++++++++++++++++++++++++++++----
> >  9 files changed, 92 insertions(+), 33 deletions(-)

On 5/29/26 10:46, Peter Maydell wrote:
> Peter Maydell (5):
>    docs/specs/fw_cfg: Document all architecture register layouts
>    hw/nvram/fw_cfg: Enforce standard layout for fw_cfg_init_mem_dma()
>    hw/nvram/fw_cfg: Enforce standard layout for x86 fw_cfg I/O ports
>    hw/nvram/fw_cfg: Remove support for I/O port fw_cfg without DMA
>    hw/nvram/fw_cfg: Document fw_cfg_init_mem_nodma()

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~