linux-kernel - Re: [PATCH v1 1/2] powerpc/mmiotrace: Add MMIO Tracing tool for PowerPC

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Date: Fri, 28 Jun 2024 17:02:48 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Jialong Yang <jialong.yang@...ngroup.cn>, Nicholas Piggin
 <npiggin@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>,
 "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>
Cc: luming.yu@...ngroup.cn, shenghui.qu@...ngroup.cn, Jialong Yang
 <jialong.yang@...ngroup.cn>, linuxppc-dev@...ts.ozlabs.org,
 linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>, Masami
 Hiramatsu <mhiramat@...nel.org>, Karol Herbst <karolherbst@...il.com>,
 Pekka Paalanen <ppaalanen@...il.com>, nouveau@...ts.freedesktop.org
Subject: Re: [PATCH v1 1/2] powerpc/mmiotrace: Add MMIO Tracing tool for
 PowerPC

Jialong Yang <jialong.yang@...ngroup.cn> writes:
> mmiotrace is a useful tool to trace MMIO accesses. Nowadays, it only
> supported on x86 and x86_64 platforms.

I've never used mmiotrace, and don't know it well.

I'm not necessarily opposed to merging it, but AFAIK it was mostly used
for reverse engineering proprietary drivers, where the driver itself
couldn't be easily instrumented. Is that what you're using it for?

For drivers where we have the source wouldn't it be easier to just use
tracepoints in the MMIO accessors?

Is it still in-use/maintained on the x86 side?

> Here is a support for powerpc.
> The manual is located at Documentation/trace/mmiotrace.rst which means
> I have not changed user API. People will be easy to use it.
> Almost all files are copied from x86/mm, there are only some
> differences from hardware and architectures software.
>
> LINK: https://lore.kernel.org/lkml/20080127195536.50809974@daedalus.pq.iki.fi/
>
> Signed-off-by: Jialong Yang <jialong.yang@...ngroup.cn>
> ---
>  arch/powerpc/Kconfig.debug       |   3 +
>  arch/powerpc/mm/Makefile         |   1 +
>  arch/powerpc/mm/kmmio.c          | 649 +++++++++++++++++++++++++++++++
>  arch/powerpc/mm/mmio-mod.c       | 414 ++++++++++++++++++++
>  arch/powerpc/mm/mmiotrace_arch.c | 149 +++++++
>  arch/powerpc/mm/mmiotrace_arch.h |  25 ++
>  arch/powerpc/mm/pf_in.c          | 185 +++++++++
>  arch/powerpc/mm/pf_in.h          |  33 ++
>  8 files changed, 1459 insertions(+)

At a glance most of that code could be shared between arches. I don't
think I can merge that as-is, without some attempt to split the generic
parts out.

cheers