From mboxrd@z Thu Jan  1 00:00:00 1970
From: Will Deacon <will.deacon@arm.com>
Subject: Re: [RFC PATCH 3/3] dynamic_debug: Add support for dynamic register
 trace
Date: Tue, 7 Aug 2018 17:57:14 +0100
Message-ID: <20180807165713.GJ21809@arm.com>
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To: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Cc: Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@redhat.com>, Laura Abbott <labbott@redhat.com>, Kees Cook <keescook@chromium.org>, Anton Vorontsov <anton@enomsg.org>, Colin Cross <ccross@android.com>, Jason Baron <jbaron@akamai.com>, Tony Luck <tony.luck@intel.com>, Arnd Bergmann <arnd@arndb.de>, Catalin Marinas <catalin.marinas@arm.com>, Joel Fernandes <joel@joelfernandes.org>, Masami Hiramatsu <mhiramat@kernel.org>, Joe Perches <joe@perches.com>, Jim Cromie <jim.cromie@gmail.com>, Rajendra Nayak <rnayak@codeaurora.org>, Vivek Gautam <vivek.gautam@codeaurora.org>, Sibi Sankar <sibis@codeaurora.org>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, Greg Kroah-Hartman <gregkh@linuxfoun>
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On Fri, Aug 03, 2018 at 07:58:44PM +0530, Sai Prakash Ranjan wrote:
> Introduce dynamic debug filtering mechanism to register
> tracing as dynamic_rtb() which will reduce a lot of
> overhead otherwise of tracing all the register reads/writes
> in all files.
> 
> Now we can just specify the file name or any wildcard pattern
> as any other dynamic debug facility in bootargs and dynamic rtb
> will just trace them and the output can be seen in pstore.
> 
> TODO: Now we use same 'p' flag but will add a separate flag for register trace
> later.
> 
> Example for tracing all register reads/writes in drivers/soc/qcom/* below:
> 
>   # dyndbg="file drivers/soc/qcom/* +p" in bootargs
>   # reboot -f
>   # mount -t pstore pstore /sys/fs/pstore
>   # cat /sys/fs/pstore/rtb-ramoops-0
>     [LOGK_WRITEL ] ts:1373030419  data:ffff00000d5065a4  <ffff00000867cb44>  qcom_smsm_probe+0x51c/0x668
>     [LOGK_WRITEL ] ts:1373360576  data:ffff00000d506608  <ffff00000867cb44>  qcom_smsm_probe+0x51c/0x668
> 
> Also we add uncached_logk api to readl/writel definitions for arm64
> as of now. This can be extended to arm as well later for tracing.
> 
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
> ---
>  arch/arm64/include/asm/io.h   | 93 +++++++++++++++++++++++++++++++++++

Putting all of this in the arch code, which basically duplicates everything,
feels very wrong to me. Perhaps take a look at the ongoing work for
instrumenting the atomics and take some inspiration from there?

Ideally, the architecture just needs to provide the low-level primivites
(which it already does) and the core can generate instruments versions if
required.

Will