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Message-ID: <20240102152023.GA2821956-robh@kernel.org>
Date: Tue, 2 Jan 2024 08:20:23 -0700
From: Rob Herring <robh@...nel.org>
To: Alexander Graf <graf@...zon.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, linux-mm@...ck.org, devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, kexec@...ts.infradead.org, linux-doc@...r.kernel.org, x86@...nel.org, Eric Biederman <ebiederm@...ssion.com>, "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Steven Rostedt <rostedt@...dmis.org>, Andrew Morton <akpm@...ux-foundation.org>, Mark Rutland <mark.rutland@....com>, Tom Lendacky <thomas.lendacky@....com>, Ashish Kalra <ashish.kalra@....com>, James Gowans <jgowans@...zon.com>, Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>, arnd@...db.de, pbonzini@...hat.com, madvenka@...ux.microsoft.com, Anthony Yznaga <anthony.yznaga@...cle.com>, Usama Arif <usama.arif@...edance.com>, David Woodhouse <dwmw@...zon.co.uk>, Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH v2 17/17] devicetree: Add bindings for ftrace KHO
On Fri, Dec 22, 2023 at 07:51:44PM +0000, Alexander Graf wrote:
> With ftrace in KHO, we are creating an ABI between old kernel and new
> kernel about the state that they transfer. To ensure that we document
> that state and catch any breaking change, let's add its schema to the
> common devicetree bindings. This way, we can quickly reason about the
> state that gets passed.
Why so much data in DT rather than putting all this information into
memory in your own data structure and DT just has a single property
pointing to that? That's what is done with every other blob of data
passed by kexec.
>
> Signed-off-by: Alexander Graf <graf@...zon.com>
> ---
> .../bindings/kho/ftrace/ftrace-array.yaml | 46 +++++++++++++++
> .../bindings/kho/ftrace/ftrace-cpu.yaml | 56 +++++++++++++++++++
> .../bindings/kho/ftrace/ftrace.yaml | 48 ++++++++++++++++
> 3 files changed, 150 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/kho/ftrace/ftrace-array.yaml
> create mode 100644 Documentation/devicetree/bindings/kho/ftrace/ftrace-cpu.yaml
> create mode 100644 Documentation/devicetree/bindings/kho/ftrace/ftrace.yaml
>
> diff --git a/Documentation/devicetree/bindings/kho/ftrace/ftrace-array.yaml b/Documentation/devicetree/bindings/kho/ftrace/ftrace-array.yaml
> new file mode 100644
> index 000000000000..9960fefc292d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/kho/ftrace/ftrace-array.yaml
> @@ -0,0 +1,46 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/kho/ftrace/ftrace-array.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Ftrace trace array
> +
> +maintainers:
> + - Alexander Graf <graf@...zon.com>
> +
> +properties:
> + compatible:
> + enum:
> + - ftrace,array-v1
> +
> + trace_flags:
> + $ref: /schemas/types.yaml#/definitions/uint32
> + description:
> + Bitmap of all the trace flags that were enabled in the trace array at the
> + point of serialization.
> +
> +# Subnodes will be of type "ftrace,cpu-v1", one each per CPU
This can be expressed as a schema.
> +additionalProperties: true
> +
> +required:
> + - compatible
> + - trace_flags
> +
> +examples:
> + - |
> + ftrace {
> + compatible = "ftrace-v1";
> + events = <1 1 2 2 3 3>;
> +
> + global_trace {
> + compatible = "ftrace,array-v1";
> + trace_flags = < 0x3354601 >;
> +
> + cpu0 {
> + compatible = "ftrace,cpu-v1";
> + cpu = < 0x00 >;
> + mem = < 0x101000000ULL 0x38ULL 0x101000100ULL 0x1000ULL 0x101000038ULL 0x38ULL 0x101002000ULL 0x1000ULL>;
> + };
> + };
> + };
> diff --git a/Documentation/devicetree/bindings/kho/ftrace/ftrace-cpu.yaml b/Documentation/devicetree/bindings/kho/ftrace/ftrace-cpu.yaml
> new file mode 100644
> index 000000000000..58c715e93f37
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/kho/ftrace/ftrace-cpu.yaml
> @@ -0,0 +1,56 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/kho/ftrace/ftrace-cpu.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Ftrace per-CPU ring buffer contents
> +
> +maintainers:
> + - Alexander Graf <graf@...zon.com>
> +
> +properties:
> + compatible:
> + enum:
> + - ftrace,cpu-v1
> +
> + cpu:
> + $ref: /schemas/types.yaml#/definitions/uint32
'cpu' is already a defined property of type 'phandle'. While we can have
multiple types for a given property name, best practice is to avoid
that. The normal way to refer to a CPU would be a phandle to the CPU
node, but I can see that might not make sense here.
"CPU numbers" on arm64 are 64-bit values as well as they are the
CPU's MPIDR value.
> + description:
> + CPU number of the CPU that this ring buffer belonged to when it was
> + serialized.
> +
> + mem:
Too vague. Make the property name indicate what's in the memory.
> + $ref: /schemas/types.yaml#/definitions/uint32-array
> + description:
> + Array of { u64 phys_addr, u64 len } elements that describe a list of ring
> + buffer pages. Each page consists of two elements. The first element
> + describes the location of the struct buffer_page that contains metadata
> + for a given ring buffer page, such as the ring's head indicator. The
> + second element points to the ring buffer data page which contains the raw
> + trace data.
> +
> +additionalProperties: false
> +
> +required:
> + - compatible
> + - cpu
> + - mem
> +
> +examples:
> + - |
> + ftrace {
> + compatible = "ftrace-v1";
> + events = <1 1 2 2 3 3>;
> +
> + global_trace {
> + compatible = "ftrace,array-v1";
> + trace_flags = < 0x3354601 >;
> +
> + cpu0 {
> + compatible = "ftrace,cpu-v1";
> + cpu = < 0x00 >;
> + mem = < 0x101000000ULL 0x38ULL 0x101000100ULL 0x1000ULL 0x101000038ULL 0x38ULL 0x101002000ULL 0x1000ULL>;
> + };
> + };
> + };
> diff --git a/Documentation/devicetree/bindings/kho/ftrace/ftrace.yaml b/Documentation/devicetree/bindings/kho/ftrace/ftrace.yaml
> new file mode 100644
> index 000000000000..b87a64843af3
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/kho/ftrace/ftrace.yaml
> @@ -0,0 +1,48 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/kho/ftrace/ftrace.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Ftrace core data
> +
> +maintainers:
> + - Alexander Graf <graf@...zon.com>
> +
> +properties:
> + compatible:
> + enum:
> + - ftrace-v1
> +
> + events:
Again, too vague.
> + $ref: /schemas/types.yaml#/definitions/uint32-array
> + description:
> + Array of { u32 crc, u32 type } elements. Each element contains a unique
> + identifier for an event, followed by the identifier that this event had
> + in the previous kernel's trace buffers.
> +
> +# Other child nodes will be of type "ftrace,array-v1". Each of which describe
> +# a trace buffer
> +additionalProperties: true
> +
> +required:
> + - compatible
> + - events
> +
> +examples:
> + - |
> + ftrace {
This should go under /chosen. Show that here. Start the example with
'/{' to do that and not add the usual boilerplate we add when extracting
the examples.
Also, we don't need 3 examples. Just do 1 complete example here.
> + compatible = "ftrace-v1";
> + events = <1 1 2 2 3 3>;
> +
> + global_trace {
> + compatible = "ftrace,array-v1";
> + trace_flags = < 0x3354601 >;
> +
> + cpu0 {
> + compatible = "ftrace,cpu-v1";
> + cpu = < 0x00 >;
> + mem = < 0x101000000ULL 0x38ULL 0x101000100ULL 0x1000ULL 0x101000038ULL 0x38ULL 0x101002000ULL 0x1000ULL>;
> + };
> + };
> + };
> --
> 2.40.1
>
>
>
>
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