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

[Bo Gan <ganboing@gmail.com>]

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@linuxfoundation.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