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SubjectRe: [RFC PATCH 3/3] dynamic_debug: Add support for dynamic register trace
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
>> 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 <>
>> ---
>> 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.

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

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