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

[Sai Prakash Ranjan]

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 <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
> 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