Re: [PATCH V2 0/2] OMAPDSS: Enable dynamic debug printing

On Thu, 2012-09-27 at 16:20 +0530, Mahapatra, Chandrabhanu wrote:

On Wed, Sep 26, 2012 at 7:59 PM, Tomi Valkeinen [off-list ref] wrote:

quoted

This doesn't work quite correctly. The problem is in dss.h, where we
define DEBUG if CONFIG_OMAP2_DSS_DEBUG_SUPPORT is set. The thing is,
DEBUG should be defined before including the kernel headers where the
pr_debug etc are defined.

So if you try the patches without dynamic debugging enabled, you won't
get any debug outputs at all, even if CONFIG_OMAP2_DSS_DEBUG_SUPPORT is
set.

And for dynamic debug, the Kconfig help says:

If a source file is compiled with DEBUG flag set, any
pr_debug() calls in it are enabled by default, but can be
disabled at runtime as below.  Note that DEBUG flag is
turned on by many CONFIG_*DEBUG* options.

So if we have CONFIG_OMAP2_DSS_DEBUG_SUPPORT set, all the pr_debugs
should be enabled by default, which is not the case, again because DEBUG
is defined too late.

I think setting DEBUG in dss.h should be removed, and instead DEBUG
should be set in the makefile if CONFIG_OMAP2_DSS_DEBUG_SUPPORT is set.

 Tomi

Well the documentation lags in describing about the DEBUG flag. I
should have checked DYNAMIC_DEBUG in Kconfig and pr_debug definition
in printk.h file.

#if defined(CONFIG_DYNAMIC_DEBUG)
/* dynamic_pr_debug() uses pr_fmt() internally so we don't need it here */
#define pr_debug(fmt, ...) \
        dynamic_pr_debug(fmt, ##__VA_ARGS__)
#elif defined(DEBUG)
#define pr_debug(fmt, ...) \
        printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
#else
#define pr_debug(fmt, ...) \
        no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
#endif

As per the definition above pr_debug is dynamic with
CONFIG_DYNAMIC_DEBUG set or else with DEBUG set it is just a normal
kernel debug printk as you have mentioned.
I still don't get how even if DEBUG is set before DSSDBG() is defined
in dss.c pr_debug() fails to enable.

Because printk.h is included without DEBUG, thus pr_debug is defined as
no_printk.

Well anyways, how to do the same in the Makefile? I tried adding
ccflags-$(CONFIG_OMAP2_DSS_DEBUG_SUPPORT) += -DEBUG
to makefile in dss directory but of no use.

-D option for the compiler is used to set defines. So it should be
-DDEBUG

 Tomi