Re: [Qemu-devel] [PATCH V3 2/2] sdhci: Change debug prints to compile unconditionally

[Markus Armbruster]

Sai Pavan Boddu <address@hidden> writes:

> Hi Markus,
>
>> -----Original Message-----
>> From: Markus Armbruster [mailto:address@hidden
>> Sent: Monday, September 07, 2015 2:35 PM
>> To: Sai Pavan Boddu
>> Cc: address@hidden; Alistair Francis; address@hidden;
>> address@hidden; Edgar Iglesias
>> Subject: Re: [Qemu-devel] [PATCH V3 2/2] sdhci: Change debug prints to
>> compile unconditionally
>> 
>> Sai Pavan Boddu <address@hidden> writes:
>> 
>> >> -----Original Message-----
>> >> From: Markus Armbruster [mailto:address@hidden
>> >> Sent: Monday, September 07, 2015 1:05 PM
>> >> To: Sai Pavan Boddu
>> >> Cc: address@hidden; address@hidden;
>> >> address@hidden; address@hidden; Sai Pavan Boddu; Edgar
>> >> Iglesias; Alistair Francis
>> >> Subject: Re: [Qemu-devel] [PATCH V3 2/2] sdhci: Change debug prints to
>> >> compile unconditionally
>> >>
>> >> Sai Pavan Boddu <address@hidden> writes:
>> >>
>> >> > Conditionaly compilation hides few type mismatch warnings, fix it to
>> >> > compile unconditioinal.
>> >> >
>> >> > Signed-off-by: Sai Pavan Boddu <address@hidden>
>> >> > Suggested-by: Eric Blake <address@hidden>
>> >>
>> >> No objection to this patch, but have you considered tracepoints?
>> >> See docs/tracing.txt.
>> >
>> > [Sai Pavan ] No, I didn’t do that. Actually no knowledge on that. Let
>> > me figure it out what it does. Even better if you can just explain in
>> > few lines, for what trace tool is used?
>> 
>> For a simple example of how to convert from debug prints to tracepoints,
>> check out commit f6e3534.
>> 
>> Perhaps the simplest way to get the debugging output then is the
>> "stderr" backend you get with "configure --enable-trace-backend=stderr".
>> Run QEMU with "-trace events=foo", where file foo contains a list of
>> events to enable.  To get all the tracepoints added by the commit above,
>> try this one-element list:
>> 
>>     fw_cfg_*
>> 
>> Hope this suffices to get you started.
>
> [Sai Pavan ] Thanks, this was useful. And I even tried to apply the
> same to sdhci. And the problems I faced in using this are as below.
>
> -> Present sdhci debug prints are not event oriented. i.e they are
> generic, so the number of arguments are changing for most of the
> DPRINT markers. Is there a way trace-events can manage variable
> arguments rather that fixed debug string and fixed number of
> arguments.
>
> i.e consider two prints like below, and convert them to use  trace_debug
>
> DPRINT("Read From %lx",READ_REG);
> DPRINT("Write to %lx with mask %lx",WRITE_REG, WRITE_MASK);
>
> We need to use two trace_debug* fuctions, as these are two different
> events. We cannot generically use the same for both.

Yes.  As in commit f6e3534, every DPRINT() becomes a distinct
tracepoint.

> -> And even the format specifiers cannot be changed as everything here
> is happening at run time.
>
> Yes, that was a very good idea to use trace tool. But much changes are
> needed in present code to get the same implementation. Will create the
> patches implementing the same later.
>
> Anyways that was a good intro to the tracer. Thanks!

You're welcome.