rvtrace: Add SiFive pre-ratified trace device support [LWN.net]

From:		Eric Lin <eric.lin-AT-sifive.com>
To:		Mayuresh Chitale <mchitale-AT-gmail.com>, Anup Patel <anup-AT-brainfault.org>, Rob Herring <robh-AT-kernel.org>, Krzysztof Kozlowski <krzk+dt-AT-kernel.org>, Conor Dooley <conor+dt-AT-kernel.org>, Paul Walmsley <pjw-AT-kernel.org>, Palmer Dabbelt <palmer-AT-dabbelt.com>, Albert Ou <aou-AT-eecs.berkeley.edu>, Alexandre Ghiti <alex-AT-ghiti.fr>, Samuel Holland <samuel.holland-AT-sifive.com>, Alexander Shishkin <alexander.shishkin-AT-linux.intel.com>
Subject:		[PATCH RFC 00/12] rvtrace: Add SiFive pre-ratified trace device support
Date:		Tue, 30 Jun 2026 17:46:23 +0800
Message-ID:		<20260630-dev-ericl-riscv_trace_support_v3-new_sifive-v3-v1-0-c9c1ffc64e4b@sifive.com>
Cc:		linux-riscv-AT-lists.infradead.org, devicetree-AT-vger.kernel.org, linux-kernel-AT-vger.kernel.org, Greentime Hu <greentime.hu-AT-sifive.com>, Eric Lin <dslin1010-AT-gmail.com>, Eric Lin <eric.lin-AT-sifive.com>, Nick Hu <nick.hu-AT-sifive.com>, Vincent Chen <vincent.chen-AT-sifive.com>
Archive-link:		Article

This series adds support for SiFive's pre-ratified trace devices on
top of the Linux RISC-V trace framework patch set [1].

The pre-ratified trace hardware is not fully compliant with the
RISC-V trace specification. The key differences are as follows:

1) The pre-ratified trace component major version is 0, and the
   implementation register bitfields are different. PATCH 2
   introduces a get_impl() callback to translate the pre-ratified
   hardware implementation register information into the standard
   RISC-V trace implementation register format.

2) A pre-ratified trace component might support different trace
   sinks, and its trace sink availability information is embedded
   within the implementation register. PATCH 3 introduces a
   get_data() callback to retrieve the component's supported trace
   sinks.

3) For routing trace data from a source to an output trace component,
   the pre-ratified hardware needs to configure the current
   component's control MMIO register, which differs from the standard
   RISC-V trace. PATCH 4 passes 'struct rvtrace_path_node' to the
   start callback to provide full path topology information,
   supporting data flow control for both ratified and pre-ratified
   trace components.

4) Unlike the standard RISC-V trace RAM sink, which is an independent
   device, the pre-ratified RAM sinks are embedded within the trace
   encoder or funnel MMIO registers and utilize a different register
   layout. PATCH 8 introduces 'struct rvtrace_ramsink_regs' to
   abstract register offsets, allowing pre-ratified trace sinks to
   leverage the existing rvtrace_ramsink_setup() functions.

This patch series has been tested on the HiFive Premier P550 board,
and the resulting trace logs match expectations.

Note: The PATCH 12 reset RAM sink write pointer on every context switch
      to avoid wrap quickly.

[1] https://lore.kernel.org/linux-riscv/20260429125135.198349...

Signed-off-by: Eric Lin <eric.lin@sifive.com>
---
Eric Lin (12):
      dt-bindings: riscv: Add SiFive pre-ratified trace components
      rvtrace: Add pre-ratified implementation callback
      rvtrace: Add pre-ratified private data callback
      rvtrace: Pass struct rvtrace_path_node to start callback
      rvtrace: encoder: Add pre-ratified support
      rvtrace: Add pre-ratified trace sink config
      rvtrace: Add pre-ratified trace funnel driver
      rvtrace: Introduce struct rvtrace_ramsink_regs to abstract register offsets
      rvtrace: Add pre-ratified ramsink setup
      rvtrace: Add copyto_auxbuf callback for pre-ratified encoder and funnel
      rvtrace: encoder: Add probe success message
      rvtrace: Reset RAM sink write pointer on every context switch

 .../bindings/riscv/riscv,trace-component.yaml      |  73 ++++++++-
 drivers/hwtracing/rvtrace/Kconfig                  |  16 ++
 drivers/hwtracing/rvtrace/Makefile                 |   2 +
 drivers/hwtracing/rvtrace/rvtrace-core.c           |  42 +++---
 drivers/hwtracing/rvtrace/rvtrace-encoder.c        |  54 +++++--
 drivers/hwtracing/rvtrace/rvtrace-funnel.c         | 127 ++++++++++++++++
 drivers/hwtracing/rvtrace/rvtrace-platform.c       |  32 +++-
 drivers/hwtracing/rvtrace/rvtrace-ramsink.c        | 166 +++++++++++++++------
 drivers/hwtracing/rvtrace/rvtrace-ramsink.h        |  13 ++
 drivers/hwtracing/rvtrace/rvtrace-v0.c             | 130 ++++++++++++++++
 drivers/hwtracing/rvtrace/rvtrace-v0.h             |  65 ++++++++
 include/linux/rvtrace.h                            |  26 +++-
 12 files changed, 658 insertions(+), 88 deletions(-)
---
base-commit: 79783024b7bd12897e21fecfaf6ac7dad02a8f0e
change-id: 20260630-dev-ericl-riscv_trace_support_v3-new_sifive-v3-e4534f9b45fd

Best regards,
--  
Eric Lin <eric.lin@sifive.com>