[v9,2/8] drm/print: Fix and add support for NULL as first argument in drm_* macros

  Comments say macros DRM_DEBUG_* are deprecated in favor of
drm_dbg_*(NULL, ...), but they have broken support for it,
as the macro will result in `(NULL) ? (NULL)->dev : NULL`.

Thus, fix them by separating logic to get dev ptr in a new
function, which will return the dev ptr if arg is not NULL.
Use it in drm_dbg_*, and also in __DRM_DEFINE_DBG_RATELIMITED,
where a similar (but correct) NULL check was in place.

Also, add support for NULL in __drm_printk, so that all the
drm_* macros will hence support NULL as the first argument.
This also means that deprecation comments mentioning pr_()*
can now be changed to the drm equivalents.

Signed-off-by: Siddh Raman Pant <code@siddh.me>
---
 include/drm/drm_print.h | 79 +++++++++++++++++++++++++++--------------
 1 file changed, 52 insertions(+), 27 deletions(-)
  

Hi Siddh,

Thank you for the patch.

On Tue, Jun 06, 2023 at 04:15:16PM +0530, Siddh Raman Pant wrote:
> Comments say macros DRM_DEBUG_* are deprecated in favor of
> drm_dbg_*(NULL, ...), but they have broken support for it,
> as the macro will result in `(NULL) ? (NULL)->dev : NULL`.

What's the problem there ?

> Thus, fix them by separating logic to get dev ptr in a new
> function, which will return the dev ptr if arg is not NULL.
> Use it in drm_dbg_*, and also in __DRM_DEFINE_DBG_RATELIMITED,
> where a similar (but correct) NULL check was in place.
> 
> Also, add support for NULL in __drm_printk, so that all the
> drm_* macros will hence support NULL as the first argument.
> This also means that deprecation comments mentioning pr_()*
> can now be changed to the drm equivalents.
> 
> Signed-off-by: Siddh Raman Pant <code@siddh.me>
> ---
>  include/drm/drm_print.h | 79 +++++++++++++++++++++++++++--------------
>  1 file changed, 52 insertions(+), 27 deletions(-)
> 
> diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
> index a93a387f8a1a..4b8532cf2ae6 100644
> --- a/include/drm/drm_print.h
> +++ b/include/drm/drm_print.h
> @@ -34,6 +34,7 @@
>  #include <linux/dynamic_debug.h>
>  
>  #include <drm/drm.h>
> +#include <drm/drm_device.h>
>  
>  /* Do *not* use outside of drm_print.[ch]! */
>  extern unsigned long __drm_debug;
> @@ -451,9 +452,32 @@ void __drm_dev_dbg(struct _ddebug *desc, const struct device *dev,
>   * Prefer drm_device based logging over device or prink based logging.
>   */
>  
> +/* Helpers for struct drm_device based logging. */
> +
> +/**
> + * __drm_dev_ptr - Helper function to get drm->dev pointer.
> + * @drm: struct drm_device pointer.
> + *
> + * RETURNS:
> + * The struct device pointer (NULL if @drm is NULL).
> + */
> +static inline struct device *__drm_dev_ptr(const struct drm_device *drm)
> +{
> +	if (drm)
> +		return drm->dev;
> +
> +	return NULL;
> +}
> +
>  /* Helper for struct drm_device based logging. */
>  #define __drm_printk(drm, level, type, fmt, ...)			\
> -	dev_##level##type((drm)->dev, "[drm] " fmt, ##__VA_ARGS__)
> +({									\
> +	struct device *__dev_ = __drm_dev_ptr(drm);			\
> +	if (__dev_)							\
> +		dev_##level##type(__dev_, "[drm] " fmt, ##__VA_ARGS__);	\
> +	else								\
> +		pr_##level##type("[drm] " fmt, ##__VA_ARGS__);		\

If I recall correctly, dev_*() handle a NULL dev pointer just fine. Do
we need to manually fall back to pr_*() ?

> +})
>  
>  
>  #define drm_info(drm, fmt, ...)					\
> @@ -487,25 +511,25 @@ void __drm_dev_dbg(struct _ddebug *desc, const struct device *dev,
>  
>  
>  #define drm_dbg_core(drm, fmt, ...)					\
> -	drm_dev_dbg((drm) ? (drm)->dev : NULL, DRM_UT_CORE, fmt, ##__VA_ARGS__)
> -#define drm_dbg_driver(drm, fmt, ...)						\
> -	drm_dev_dbg((drm) ? (drm)->dev : NULL, DRM_UT_DRIVER, fmt, ##__VA_ARGS__)
> +	drm_dev_dbg(__drm_dev_ptr(drm), DRM_UT_CORE, fmt, ##__VA_ARGS__)
> +#define drm_dbg_driver(drm, fmt, ...)					\
> +	drm_dev_dbg(__drm_dev_ptr(drm), DRM_UT_DRIVER, fmt, ##__VA_ARGS__)
>  #define drm_dbg_kms(drm, fmt, ...)					\
> -	drm_dev_dbg((drm) ? (drm)->dev : NULL, DRM_UT_KMS, fmt, ##__VA_ARGS__)
> +	drm_dev_dbg(__drm_dev_ptr(drm), DRM_UT_KMS, fmt, ##__VA_ARGS__)
>  #define drm_dbg_prime(drm, fmt, ...)					\
> -	drm_dev_dbg((drm) ? (drm)->dev : NULL, DRM_UT_PRIME, fmt, ##__VA_ARGS__)
> +	drm_dev_dbg(__drm_dev_ptr(drm), DRM_UT_PRIME, fmt, ##__VA_ARGS__)
>  #define drm_dbg_atomic(drm, fmt, ...)					\
> -	drm_dev_dbg((drm) ? (drm)->dev : NULL, DRM_UT_ATOMIC, fmt, ##__VA_ARGS__)
> +	drm_dev_dbg(__drm_dev_ptr(drm), DRM_UT_ATOMIC, fmt, ##__VA_ARGS__)
>  #define drm_dbg_vbl(drm, fmt, ...)					\
> -	drm_dev_dbg((drm) ? (drm)->dev : NULL, DRM_UT_VBL, fmt, ##__VA_ARGS__)
> +	drm_dev_dbg(__drm_dev_ptr(drm), DRM_UT_VBL, fmt, ##__VA_ARGS__)
>  #define drm_dbg_state(drm, fmt, ...)					\
> -	drm_dev_dbg((drm) ? (drm)->dev : NULL, DRM_UT_STATE, fmt, ##__VA_ARGS__)
> +	drm_dev_dbg(__drm_dev_ptr(drm), DRM_UT_STATE, fmt, ##__VA_ARGS__)
>  #define drm_dbg_lease(drm, fmt, ...)					\
> -	drm_dev_dbg((drm) ? (drm)->dev : NULL, DRM_UT_LEASE, fmt, ##__VA_ARGS__)
> +	drm_dev_dbg(__drm_dev_ptr(drm), DRM_UT_LEASE, fmt, ##__VA_ARGS__)
>  #define drm_dbg_dp(drm, fmt, ...)					\
> -	drm_dev_dbg((drm) ? (drm)->dev : NULL, DRM_UT_DP, fmt, ##__VA_ARGS__)
> +	drm_dev_dbg(__drm_dev_ptr(drm), DRM_UT_DP, fmt, ##__VA_ARGS__)
>  #define drm_dbg_drmres(drm, fmt, ...)					\
> -	drm_dev_dbg((drm) ? (drm)->dev : NULL, DRM_UT_DRMRES, fmt, ##__VA_ARGS__)
> +	drm_dev_dbg(__drm_dev_ptr(drm), DRM_UT_DRMRES, fmt, ##__VA_ARGS__)
>  
>  #define drm_dbg(drm, fmt, ...)	drm_dbg_driver(drm, fmt, ##__VA_ARGS__)
>  
> @@ -533,31 +557,31 @@ void __drm_err(const char *format, ...);
>  #define _DRM_PRINTK(once, level, fmt, ...)				\
>  	printk##once(KERN_##level "[" DRM_NAME "] " fmt, ##__VA_ARGS__)
>  
> -/* NOTE: this is deprecated in favor of pr_info(). */
> +/* NOTE: this is deprecated in favor of drm_info(NULL, ...). */
>  #define DRM_INFO(fmt, ...)						\
>  	_DRM_PRINTK(, INFO, fmt, ##__VA_ARGS__)
> -/* NOTE: this is deprecated in favor of pr_notice(). */
> +/* NOTE: this is deprecated in favor of drm_notice(NULL, ...). */
>  #define DRM_NOTE(fmt, ...)						\
>  	_DRM_PRINTK(, NOTICE, fmt, ##__VA_ARGS__)
> -/* NOTE: this is deprecated in favor of pr_warn(). */
> +/* NOTE: this is deprecated in favor of drm_warn(NULL, ...). */
>  #define DRM_WARN(fmt, ...)						\
>  	_DRM_PRINTK(, WARNING, fmt, ##__VA_ARGS__)
>  
> -/* NOTE: this is deprecated in favor of pr_info_once(). */
> +/* NOTE: this is deprecated in favor of drm_info_once(NULL, ...). */
>  #define DRM_INFO_ONCE(fmt, ...)						\
>  	_DRM_PRINTK(_once, INFO, fmt, ##__VA_ARGS__)
> -/* NOTE: this is deprecated in favor of pr_notice_once(). */
> +/* NOTE: this is deprecated in favor of drm_notice_once(NULL, ...). */
>  #define DRM_NOTE_ONCE(fmt, ...)						\
>  	_DRM_PRINTK(_once, NOTICE, fmt, ##__VA_ARGS__)
> -/* NOTE: this is deprecated in favor of pr_warn_once(). */
> +/* NOTE: this is deprecated in favor of drm_warn_once(NULL, ...). */
>  #define DRM_WARN_ONCE(fmt, ...)						\
>  	_DRM_PRINTK(_once, WARNING, fmt, ##__VA_ARGS__)
>  
> -/* NOTE: this is deprecated in favor of pr_err(). */
> +/* NOTE: this is deprecated in favor of drm_err(NULL, ...). */
>  #define DRM_ERROR(fmt, ...)						\
>  	__drm_err(fmt, ##__VA_ARGS__)
>  
> -/* NOTE: this is deprecated in favor of pr_err_ratelimited(). */
> +/* NOTE: this is deprecated in favor of drm_err_ratelimited(NULL, ...). */
>  #define DRM_ERROR_RATELIMITED(fmt, ...)					\
>  	DRM_DEV_ERROR_RATELIMITED(NULL, fmt, ##__VA_ARGS__)
>  
> @@ -593,13 +617,14 @@ void __drm_err(const char *format, ...);
>  #define DRM_DEBUG_DP(fmt, ...)						\
>  	__drm_dbg(DRM_UT_DP, fmt, ## __VA_ARGS__)
>  
> -#define __DRM_DEFINE_DBG_RATELIMITED(category, drm, fmt, ...)					\
> -({												\
> -	static DEFINE_RATELIMIT_STATE(rs_, DEFAULT_RATELIMIT_INTERVAL, DEFAULT_RATELIMIT_BURST);\
> -	const struct drm_device *drm_ = (drm);							\
> -												\
> -	if (drm_debug_enabled(DRM_UT_ ## category) && __ratelimit(&rs_))			\
> -		drm_dev_printk(drm_ ? drm_->dev : NULL, KERN_DEBUG, fmt, ## __VA_ARGS__);	\
> +#define __DRM_DEFINE_DBG_RATELIMITED(category, drm, fmt, ...)		\
> +({									\
> +	static DEFINE_RATELIMIT_STATE(rs_, DEFAULT_RATELIMIT_INTERVAL,	\
> +				      DEFAULT_RATELIMIT_BURST);		\
> +									\
> +	if (drm_debug_enabled(DRM_UT_ ## category) && __ratelimit(&rs_))\
> +		drm_dev_printk(__drm_dev_ptr(drm), KERN_DEBUG,		\
> +			       fmt, ## __VA_ARGS__);			\
>  })
>  
>  #define drm_dbg_kms_ratelimited(drm, fmt, ...) \
  

On Tue, 06 Jun 2023 19:35:12 +0530, Laurent Pinchart wrote:
> Hi Siddh,
> 
> Thank you for the patch.

Anytime :)

> On Tue, Jun 06, 2023 at 04:15:16PM +0530, Siddh Raman Pant wrote:
> > Comments say macros DRM_DEBUG_* are deprecated in favor of
> > drm_dbg_*(NULL, ...), but they have broken support for it,
> > as the macro will result in `(NULL) ? (NULL)->dev : NULL`.
> 
> What's the problem there ?

(NULL)->dev is invalid C. It's a macro, so preprocessor substitutes
that text directly, there is no evaluation. GCC will throw an error
regarding dereferencing a void* pointer.

> >  /* Helper for struct drm_device based logging. */
> >  #define __drm_printk(drm, level, type, fmt, ...)                     \
> > -     dev_##level##type((drm)->dev, "[drm] " fmt, ##__VA_ARGS__)
> > +({                                                                   \
> > +     struct device *__dev_ = __drm_dev_ptr(drm);                     \
> > +     if (__dev_)                                                     \
> > +             dev_##level##type(__dev_, "[drm] " fmt, ##__VA_ARGS__); \
> > +     else                                                            \
> > +             pr_##level##type("[drm] " fmt, ##__VA_ARGS__);          \
> 
> If I recall correctly, dev_*() handle a NULL dev pointer just fine. Do
> we need to manually fall back to pr_*() ?

I took drm_dev_printk (on line 261 of drm_print.c) as the reference,
wherein it uses a conditional for determining whether dev_printk or
printk should be called.

I suppose it is to avoid printing "(NULL device *)", which dev_printk
does if it gets a NULL device pointer (refer the definition on line
4831 of drivers/base/core.c). Though if I'm wrong, kindly let me know.

Thanks,
Siddh
  

On Tue, Jun 06, 2023 at 08:04:39PM +0530, Siddh Raman Pant wrote:
> On Tue, 06 Jun 2023 19:35:12 +0530, Laurent Pinchart wrote:
> > Hi Siddh,
> > 
> > Thank you for the patch.
> 
> Anytime :)
> 
> > On Tue, Jun 06, 2023 at 04:15:16PM +0530, Siddh Raman Pant wrote:
> > > Comments say macros DRM_DEBUG_* are deprecated in favor of
> > > drm_dbg_*(NULL, ...), but they have broken support for it,
> > > as the macro will result in `(NULL) ? (NULL)->dev : NULL`.
> > 
> > What's the problem there ?
> 
> (NULL)->dev is invalid C. It's a macro, so preprocessor substitutes
> that text directly, there is no evaluation. GCC will throw an error
> regarding dereferencing a void* pointer.
> 
> > >  /* Helper for struct drm_device based logging. */
> > >  #define __drm_printk(drm, level, type, fmt, ...)                     \
> > > -     dev_##level##type((drm)->dev, "[drm] " fmt, ##__VA_ARGS__)
> > > +({                                                                   \
> > > +     struct device *__dev_ = __drm_dev_ptr(drm);                     \
> > > +     if (__dev_)                                                     \
> > > +             dev_##level##type(__dev_, "[drm] " fmt, ##__VA_ARGS__); \
> > > +     else                                                            \
> > > +             pr_##level##type("[drm] " fmt, ##__VA_ARGS__);          \
> > 
> > If I recall correctly, dev_*() handle a NULL dev pointer just fine. Do
> > we need to manually fall back to pr_*() ?
> 
> I took drm_dev_printk (on line 261 of drm_print.c) as the reference,
> wherein it uses a conditional for determining whether dev_printk or
> printk should be called.
> 
> I suppose it is to avoid printing "(NULL device *)", which dev_printk
> does if it gets a NULL device pointer (refer the definition on line
> 4831 of drivers/base/core.c). Though if I'm wrong, kindly let me know.

You're right, it's probably best to avoid the "(NULL device *)".

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>