Re: [PATCH] drm/amd/display: Make BREAK_TO_DEBUGGER() a debug print

[Michel Dänzer]

On 2020-05-22 8:03 p.m., Nicholas Kazlauskas wrote:
> [Why]
> Warnings in the kernel are generally treated as errors.
> 
> The BREAK_TO_DEBUGGER macro is not a critical error or warning, but
> rather intended for developer use to help investigate behavior and
> sequences for other issues.
> 
> We do still make use of DC_ERROR/ASSERT(0) in various places in the
> code for things that are genuine issues.
> 
> Since most developers don't actually KGDB while debugging the kernel
> these essentially would have no value on their own since the KGDB
> breakpoint wouldn't trigger - ASSERT(0) was used as a shortcut to get
> a stacktrace.
> 
> [How]
> Turn it into a DRM_DEBUG_DRIVER print instead. We unfortunately lose
> the stacktrace, but we still do retain some of the useful debug
> information this offers by having at least the function and line
> number loggable.
> 
> If KGDB is supported in the kernel this will still trigger a real
> breakpoint as well.

Not sure this makes sense now that WARN_ON_ONCE is used for ASSERT().
The name "BREAK_TO_DEBUGGER" implies that something unexpected happened
which needs to be investigated, so having a backtrace seems important to me.


-- 
Earthling Michel Dänzer   |   https://redhat.com
Libre software enthusiast | Mesa and X developer
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Re: [PATCH] drm/amd/display: Make BREAK_TO_DEBUGGER() a debug print

[Harry Wentland]

On 2020-05-22 2:03 p.m., Nicholas Kazlauskas wrote:
> [Why]
> Warnings in the kernel are generally treated as errors.
> 
> The BREAK_TO_DEBUGGER macro is not a critical error or warning, but
> rather intended for developer use to help investigate behavior and
> sequences for other issues.
> 
> We do still make use of DC_ERROR/ASSERT(0) in various places in the
> code for things that are genuine issues.
> 
> Since most developers don't actually KGDB while debugging the kernel
> these essentially would have no value on their own since the KGDB
> breakpoint wouldn't trigger - ASSERT(0) was used as a shortcut to get
> a stacktrace.
> 
> [How]
> Turn it into a DRM_DEBUG_DRIVER print instead. We unfortunately lose
> the stacktrace, but we still do retain some of the useful debug
> information this offers by having at least the function and line
> number loggable.
> 
> If KGDB is supported in the kernel this will still trigger a real
> breakpoint as well.
> 
> Cc: Harry Wentland 
> Cc: Leo Li 
> Cc: Bhawanpreet Lakha 
> Cc: Rodrigo Siqueira 
> Signed-off-by: Nicholas Kazlauskas 

Reviewed-by: Harry Wentland 

Harry

> ---
>  drivers/gpu/drm/amd/display/dc/os_types.h | 10 +-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/os_types.h 
> b/drivers/gpu/drm/amd/display/dc/os_types.h
> index 6d7bca562eec..604ceb6c0375 100644
> --- a/drivers/gpu/drm/amd/display/dc/os_types.h
> +++ b/drivers/gpu/drm/amd/display/dc/os_types.h
> @@ -111,7 +111,15 @@
>  #define ASSERT(expr) WARN_ON_ONCE(!(expr))
>  #endif
>  
> -#define BREAK_TO_DEBUGGER() ASSERT(0)
> +#if defined(CONFIG_HAVE_KGDB) || defined(CONFIG_KGDB)
> +#define BREAK_TO_DEBUGGER() \
> + do { \
> + DRM_DEBUG_DRIVER("%s():%d\n", __func__, __LINE__); \
> + kgdb_breakpoint(); \
> + } while (0)
> +#else
> +#define BREAK_TO_DEBUGGER() DRM_DEBUG_DRIVER("%s():%d\n", __func__, __LINE__)
> +#endif
>  
>  #define DC_ERR(...)  do { \
>   dm_error(__VA_ARGS__); \
> 
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