Subject: Re: [PATCH v5 4/4] devicetree: update documentation for fw_cfg ARM
 bindings
To: "Gabriel L. Somlo" <somlo@cmu.edu>, gregkh@linuxfoundation.org,
        robh+dt@kernel.org, pawel.moll@arm.com, mark.rutland@arm.com,
        ijc+devicetree@hellion.org.uk, galak@codeaurora.org, arnd@arndb.de,
        ralf@linux-mips.org, rmk+kernel@arm.linux.org.uk, eric@anholt.net,
        hanjun.guo@linaro.org, zajec5@gmail.com, sudeep.holla@arm.com,
        agross@codeaurora.org, linux-api@vger.kernel.org,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
References: <1448294264-17388-1-git-send-email-somlo@cmu.edu>
 <1448294264-17388-5-git-send-email-somlo@cmu.edu>
Cc: qemu-devel@nongnu.org, jordan.l.justen@intel.com, mst@redhat.com,
        peter.maydell@linaro.org, leif.lindholm@linaro.org,
        ard.biesheuvel@linaro.org, pbonzini@redhat.com, kraxel@redhat.com,
        luto@amacapital.net, stefanha@gmail.com, revol@free.fr
From: Laszlo Ersek <lersek@redhat.com>
Message-ID: <56534067.6040401@redhat.com>
Date: Mon, 23 Nov 2015 17:35:51 +0100
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On 11/23/15 16:57, Gabriel L. Somlo wrote:
> From: Gabriel Somlo <somlo@cmu.edu>
> 
> Remove fw_cfg hardware interface details from
> Documentation/devicetree/bindings/arm/fw-cfg.txt,
> and replace them with a pointer to the authoritative
> documentation in the QEMU source tree.
> 
> Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
> Cc: Laszlo Ersek <lersek@redhat.com>
> ---
>  Documentation/devicetree/bindings/arm/fw-cfg.txt | 38 ++----------------------
>  1 file changed, 2 insertions(+), 36 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/arm/fw-cfg.txt b/Documentation/devicetree/bindings/arm/fw-cfg.txt
> index 953fb64..ce27386 100644
> --- a/Documentation/devicetree/bindings/arm/fw-cfg.txt
> +++ b/Documentation/devicetree/bindings/arm/fw-cfg.txt
> @@ -11,43 +11,9 @@ 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 guest writes a selector value (a key) to the selector register, and then
> -can read the corresponding data (produced by QEMU) via the data register. If
> -the selected entry is writable, the guest can rewrite it through the data
> -register.
> +The authoritative guest-side hardware interface documentation to the fw_cfg
> +device ca be found in "docs/specs/fw_cfg.txt" in the QEMU source tree.

ca[n] be found

>  
> -The selector register takes keys in big endian byte order.
> -
> -The data register allows accesses with 8, 16, 32 and 64-bit width (only at
> -offset 0 of the register). Accesses larger than a byte are interpreted as
> -arrays, bundled together only for better performance. The bytes constituting
> -such a word, in increasing address order, correspond to the bytes that would
> -have been transferred by byte-wide accesses in chronological order.
> -
> -The interface allows guest firmware to download various parameters and blobs
> -that affect how the firmware works and what tables it installs for the guest
> -OS. For example, boot order of devices, ACPI tables, SMBIOS tables, kernel and
> -initrd images for direct kernel booting, virtual machine UUID, SMP information,
> -virtual NUMA topology, and so on.
> -
> -The authoritative registry of the valid selector values and their meanings is
> -the QEMU source code; the structure of the data blobs corresponding to the
> -individual key values is also defined in the QEMU source code.
> -
> -The presence of the registers can be verified by selecting the "signature" blob
> -with key 0x0000, and reading four bytes from the data register. The returned
> -signature is "QEMU".
> -
> -The outermost protocol (involving the write / read sequences of the control and
> -data registers) is expected to be versioned, and/or described by feature bits.
> -The interface revision / feature bitmap can be retrieved with key 0x0001. The
> -blob to be read from the data register has size 4, and it is to be interpreted
> -as a uint32_t value in little endian byte order. The current value
> -(corresponding to the above outer protocol) is zero.
> -
> -The guest kernel is not expected to use these registers (although it is
> -certainly allowed to); the device tree bindings are documented here because
> -this is where device tree bindings reside in general.
>  
>  Required properties:
>  
> 

As long as Peter is fine with this, I don't object.

With the typo fixed:

Reviewed-by: Laszlo Ersek <lersek@redhat.com>
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