linux-kernel - Re: [PATCH] dt-bindings: arm: Convert QEMU fw-cfg to DT schema

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Date:   Thu, 10 Mar 2022 08:19:49 -0600
From:   Rob Herring <robh@...nel.org>
To:     Laszlo Ersek <lersek@...hat.com>
Cc:     Krzysztof Kozlowski <krzk+dt@...nel.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dt-bindings: arm: Convert QEMU fw-cfg to DT schema

On Thu, Mar 10, 2022 at 10:05:04AM +0100, Laszlo Ersek wrote:
> On 03/10/22 02:35, Rob Herring wrote:
> > Convert the QEMU fw-cfg binding to DT schema format. As this binding is
> > also used on Risc-V now, drop any architecture references and move to a
> > common location. The fw-cfg interface has also gained some DMA support
> > which is coherent, so add the missing 'dma-coherent'.
> > 
> > Signed-off-by: Rob Herring <robh@...nel.org>
> > ---
> >  .../devicetree/bindings/arm/fw-cfg.txt        | 38 -------------
> >  .../bindings/firmware/qemu,fw-cfg-mmio.yaml   | 54 +++++++++++++++++++
> >  2 files changed, 54 insertions(+), 38 deletions(-)
> >  delete mode 100644 Documentation/devicetree/bindings/arm/fw-cfg.txt
> >  create mode 100644 Documentation/devicetree/bindings/firmware/qemu,fw-cfg-mmio.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/arm/fw-cfg.txt b/Documentation/devicetree/bindings/arm/fw-cfg.txt
> > deleted file mode 100644
> > index fd54e1db2156..000000000000
> > --- a/Documentation/devicetree/bindings/arm/fw-cfg.txt
> > +++ /dev/null
> > @@ -1,38 +0,0 @@
> > -* QEMU Firmware Configuration bindings for ARM
> > -
> > -QEMU's arm-softmmu and aarch64-softmmu emulation / virtualization targets
> > -provide the following Firmware Configuration interface on the "virt" machine
> > -type:
> > -
> > -- A write-only, 16-bit wide selector (or control) register,
> > -- a read-write, 64-bit wide data register.
> > -
> > -QEMU exposes the control and data register to ARM guests as memory mapped
> > -registers; their location is communicated to the guest's UEFI firmware in the
> > -DTB that QEMU places at the bottom of the guest's DRAM.
> > -
> > -The authoritative guest-side hardware interface documentation to the fw_cfg
> > -device can be found in "docs/specs/fw_cfg.txt" in the QEMU source tree.
> > -
> > -
> > -Required properties:
> > -
> > -- compatible: "qemu,fw-cfg-mmio".
> > -
> > -- reg: the MMIO region used by the device.
> > -  * Bytes 0x0 to 0x7 cover the data register.
> > -  * Bytes 0x8 to 0x9 cover the selector register.
> > -  * Further registers may be appended to the region in case of future interface
> > -    revisions / feature bits.
> > -
> > -Example:
> > -
> > -/ {
> > -	#size-cells = <0x2>;
> > -	#address-cells = <0x2>;
> > -
> > -	fw-cfg@...0000 {
> > -		compatible = "qemu,fw-cfg-mmio";
> > -		reg = <0x0 0x9020000 0x0 0xa>;
> > -	};
> > -};
> > diff --git a/Documentation/devicetree/bindings/firmware/qemu,fw-cfg-mmio.yaml b/Documentation/devicetree/bindings/firmware/qemu,fw-cfg-mmio.yaml
> > new file mode 100644
> > index 000000000000..3aac9448e7f1
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/firmware/qemu,fw-cfg-mmio.yaml
> > @@ -0,0 +1,54 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/firmware/qemu,fw-cfg-mmio.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: QEMU Firmware Configuration bindings
> > +
> > +maintainers:
> > +  - Laszlo Ersek <lersek@...hat.com>
> 
> Ugh :) I guess this is based on my authorship of historical commit
> 53275a61bc7a ("devicetree: document ARM bindings for QEMU's Firmware
> Config interface", 2015-01-13), and prehaps my R-b on commit
> 92aed5d6ba90 ("devicetree: update documentation for fw_cfg ARM
> bindings", 2016-02-09).
> 
> However -- I totally can't maintain this file. (I mean I've probably not
> done anything related to it in the past seven years, so I guess it's
> time to admit that fact!)
> 
> Rob, would you please consider taking it over?

Yeah, no problem.

> With my name+email replaced with yours:
> 
> Acked-by: Laszlo Ersek <lersek@...hat.com>
> 
> Thank you!
> Laszlo