drm/amd/display: avoid passing enum as NULL pointer

Message ID 20190307103454.1637485-1-arnd@arndb.de
State New
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Series
  • drm/amd/display: avoid passing enum as NULL pointer
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Commit Message

Arnd Bergmann March 7, 2019, 10:34 a.m.
The mod_freesync_build_vrr_infopacket() function uses rather obscure
calling conventions, where an enum is passed in through a pointer,
and a NULL pointer is expected to behave the same way as the zero-value
(TRANSFER_FUNC_UNKNOWN).

Trying to build this with clang results in a warning:

drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:4601:3: error: expression which evaluates to zero treated
      as a null pointer constant of type 'const enum color_transfer_func *' [-Werror,-Wnon-literal-null-conversion]

Passing it by value instead of by reference makes the code simpler
and more conventional but should not change the behavior at all.

Fixes: c2791297013e ("drm/amd/display: Add color bit info to freesync infoframe")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

---
 drivers/gpu/drm/amd/display/modules/freesync/freesync.c | 7 +++----
 drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h  | 2 +-
 2 files changed, 4 insertions(+), 5 deletions(-)

-- 
2.20.0

Comments

Nathan Chancellor March 7, 2019, 3:34 p.m. | #1
On Thu, Mar 07, 2019 at 11:34:29AM +0100, Arnd Bergmann wrote:
> The mod_freesync_build_vrr_infopacket() function uses rather obscure

> calling conventions, where an enum is passed in through a pointer,

> and a NULL pointer is expected to behave the same way as the zero-value

> (TRANSFER_FUNC_UNKNOWN).

> 

> Trying to build this with clang results in a warning:

> 

> drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:4601:3: error: expression which evaluates to zero treated

>       as a null pointer constant of type 'const enum color_transfer_func *' [-Werror,-Wnon-literal-null-conversion]

> 

> Passing it by value instead of by reference makes the code simpler

> and more conventional but should not change the behavior at all.

> 

> Fixes: c2791297013e ("drm/amd/display: Add color bit info to freesync infoframe")

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

> ---

>  drivers/gpu/drm/amd/display/modules/freesync/freesync.c | 7 +++----

>  drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h  | 2 +-

>  2 files changed, 4 insertions(+), 5 deletions(-)

> 

> diff --git a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c

> index 94a84bc57c7a..6f32fe129880 100644

> --- a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c

> +++ b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c

> @@ -724,7 +724,7 @@ static void build_vrr_infopacket_v1(enum signal_type signal,

>  

>  static void build_vrr_infopacket_v2(enum signal_type signal,

>  		const struct mod_vrr_params *vrr,

> -		const enum color_transfer_func *app_tf,

> +		const enum color_transfer_func app_tf,

>  		struct dc_info_packet *infopacket)

>  {

>  	unsigned int payload_size = 0;

> @@ -732,8 +732,7 @@ static void build_vrr_infopacket_v2(enum signal_type signal,

>  	build_vrr_infopacket_header_v2(signal, infopacket, &payload_size);

>  	build_vrr_infopacket_data(vrr, infopacket);

>  

> -	if (app_tf != NULL)

> -		build_vrr_infopacket_fs2_data(*app_tf, infopacket);

> +	build_vrr_infopacket_fs2_data(app_tf, infopacket);

>  

>  	build_vrr_infopacket_checksum(&payload_size, infopacket);

>  

> @@ -757,7 +756,7 @@ void mod_freesync_build_vrr_infopacket(struct mod_freesync *mod_freesync,

>  		const struct dc_stream_state *stream,

>  		const struct mod_vrr_params *vrr,

>  		enum vrr_packet_type packet_type,

> -		const enum color_transfer_func *app_tf,

> +		const enum color_transfer_func app_tf,

>  		struct dc_info_packet *infopacket)

>  {

>  	/* SPD info packet for FreeSync

> diff --git a/drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h b/drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h

> index 4222e403b151..645793b924cf 100644

> --- a/drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h

> +++ b/drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h

> @@ -145,7 +145,7 @@ void mod_freesync_build_vrr_infopacket(struct mod_freesync *mod_freesync,

>  		const struct dc_stream_state *stream,

>  		const struct mod_vrr_params *vrr,

>  		enum vrr_packet_type packet_type,

> -		const enum color_transfer_func *app_tf,

> +		const enum color_transfer_func app_tf,

>  		struct dc_info_packet *infopacket);

>  

>  void mod_freesync_build_vrr_params(struct mod_freesync *mod_freesync,

> -- 

> 2.20.0

> 


Just as an FYI, I sent the same fix when the warning first hit which was
recently accepted:

https://cgit.freedesktop.org/~agd5f/linux/commit/?id=672e78cab819ebe31e3b9b8abac367be8a110472

Just waiting for it to hit mainline.

Cheers,
Nathan

Patch

diff --git a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
index 94a84bc57c7a..6f32fe129880 100644
--- a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
+++ b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
@@ -724,7 +724,7 @@  static void build_vrr_infopacket_v1(enum signal_type signal,
 
 static void build_vrr_infopacket_v2(enum signal_type signal,
 		const struct mod_vrr_params *vrr,
-		const enum color_transfer_func *app_tf,
+		const enum color_transfer_func app_tf,
 		struct dc_info_packet *infopacket)
 {
 	unsigned int payload_size = 0;
@@ -732,8 +732,7 @@  static void build_vrr_infopacket_v2(enum signal_type signal,
 	build_vrr_infopacket_header_v2(signal, infopacket, &payload_size);
 	build_vrr_infopacket_data(vrr, infopacket);
 
-	if (app_tf != NULL)
-		build_vrr_infopacket_fs2_data(*app_tf, infopacket);
+	build_vrr_infopacket_fs2_data(app_tf, infopacket);
 
 	build_vrr_infopacket_checksum(&payload_size, infopacket);
 
@@ -757,7 +756,7 @@  void mod_freesync_build_vrr_infopacket(struct mod_freesync *mod_freesync,
 		const struct dc_stream_state *stream,
 		const struct mod_vrr_params *vrr,
 		enum vrr_packet_type packet_type,
-		const enum color_transfer_func *app_tf,
+		const enum color_transfer_func app_tf,
 		struct dc_info_packet *infopacket)
 {
 	/* SPD info packet for FreeSync
diff --git a/drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h b/drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h
index 4222e403b151..645793b924cf 100644
--- a/drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h
+++ b/drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h
@@ -145,7 +145,7 @@  void mod_freesync_build_vrr_infopacket(struct mod_freesync *mod_freesync,
 		const struct dc_stream_state *stream,
 		const struct mod_vrr_params *vrr,
 		enum vrr_packet_type packet_type,
-		const enum color_transfer_func *app_tf,
+		const enum color_transfer_func app_tf,
 		struct dc_info_packet *infopacket);
 
 void mod_freesync_build_vrr_params(struct mod_freesync *mod_freesync,