linux-kernel - Re: [PATCH 00/11] Linux RISC-V trace framework and drivers

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Message-ID: <30efd90b-ba9f-4291-b9a1-8739f1c5f24b@gmail.com>
Date: Thu, 2 Oct 2025 13:42:20 -0700
From: Bo Gan <ganboing@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>, Anup Patel <apatel@...tanamicro.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Paul Walmsley
 <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Ian Rogers <irogers@...gle.com>, Alexandre Ghiti <alex@...ti.fr>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
 Liang Kan <kan.liang@...ux.intel.com>, Mayuresh Chitale
 <mchitale@...il.com>, Anup Patel <anup@...infault.org>,
 Atish Patra <atish.patra@...ux.dev>, Andrew Jones <ajones@...tanamicro.com>,
 Sunil V L <sunilvl@...tanamicro.com>, linux-riscv@...ts.infradead.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/11] Linux RISC-V trace framework and drivers

On 10/1/25 23:44, Greg KH wrote:
> On Thu, Oct 02, 2025 at 12:09:23PM +0530, Anup Patel wrote:
>> On Thu, Oct 2, 2025 at 11:56 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>>>
>>> On Thu, Oct 02, 2025 at 11:37:21AM +0530, Anup Patel wrote:
>>>> This series adds initial support for RISC-V trace framework and drivers.
>>>> The RISC-V trace v1.0 specification is already ratified and can be found at:
>>>> https://github.com/riscv-non-isa/e-trace-encap/releases/tag/v1.0.0-ratified
>>>> https://github.com/riscv-non-isa/tg-nexus-trace/releases/tag/1.0_Ratified
>>>>
>>>> The RISC-V trace framework and drivers are designed to be agnostic to the
>>>> underlying trace protocol hence both RISC-V E-trace and RISC-V N-trace should
>>>> work fine. The discovery of trace protocl parameters are left to user-space
>>>> trace decoder.
>>>>
>>>> In ther future, there will be subsequent series adding:
>>>> 1) Sysfs support
>>>
>>> why does "trace" need sysfs support?  No other cpu platform uses that
>>> today, so why is a new user/kernel api needed?
>>
>> We saw trace support for other architectures (e.g. ARM coresight) allowing
>> trace start/stop through sysfs. If this is an obsolete or not preferred approach
>> then we will deprioritize and possibly never add it.
> 
> Why is that needed for coresight and other arches do not need it?
> Perhaps it should be deleted from that codebase instead?
> 
> thanks,
> 
> greg k-h

Hi Greg,

sysfs is helpful for controlling the trace if not utilized through perf
framework. It can also be used by userspace to discover the topology of
trace components and their capabilities. @Anup I assume this driver is
designed with other sinks in mind (not just ramsink), so it can be used
to emit trace to external probes, right?

Bo