Re: [RFC PATCH 3/3] dynamic_debug: Add support for dynamic register trace

From: Sai Prakash Ranjan
Date: Wed Aug 08 2018 - 10:29:45 EST

On 8/7/2018 10:27 PM, Will Deacon wrote:
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

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@xxxxxxxxxxxxxx>
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

Hi Will,

Thanks for the review. Will look at instrumented atomics implementation and get back. Let me know if anything else can be improved.

- Sai Prakash