[PATCH AUTOSEL 5.0 070/262] drm/amd/display: Pass app_tf by value rather than by reference

* [PATCH AUTOSEL 5.0 070/262] drm/amd/display: Pass app_tf by value rather than by reference
       [not found] ` <20190327180158.10245-1-sashal-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
@ 2019-03-27 17:58   ` Sasha Levin
  2019-03-28 10:04     ` Pavel Machek
  2019-03-27 18:00   ` [PATCH AUTOSEL 5.0 171/262] drm/amd/display: Don't re-program planes for DPMS changes Sasha Levin
  2019-03-27 18:00   ` [PATCH AUTOSEL 5.0 175/262] drm/amd/display: Disconnect mpcc when changing tg Sasha Levin
  2 siblings, 1 reply; 7+ messages in thread
From: Sasha Levin @ 2019-03-27 17:58 UTC (permalink / raw)
  To: linux-kernel-u79uwXL29TY76Z2rM5mHXA,
	stable-u79uwXL29TY76Z2rM5mHXA
  Cc: Alex Deucher, Sasha Levin, Nathan Chancellor,
	dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW,
	amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW

From: Nathan Chancellor <natechancellor@gmail.com>

[ Upstream commit 672e78cab819ebe31e3b9b8abac367be8a110472 ]

Clang warns when an expression that equals zero is used as a null
pointer constant (in lieu of NULL):

drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:4435:3:
warning: expression which evaluates to zero treated as a null pointer
constant of type 'const enum color_transfer_func *'
[-Wnon-literal-null-conversion]
                TRANSFER_FUNC_UNKNOWN,
                ^~~~~~~~~~~~~~~~~~~~~
1 warning generated.

This warning is caused by commit bb47de736661 ("drm/amdgpu: Set FreeSync
state using drm VRR properties") and it could be solved by using NULL
instead of TRANSFER_FUNC_UNKNOWN or casting TRANSFER_FUNC_UNKNOWN as a
pointer. However, after looking into it, there doesn't appear to be a
good reason to pass app_tf by reference as it is never mutated along the
way. This is the only code path in which app_tf is used:

mod_freesync_build_vrr_infopacket ->
    build_vrr_infopacket_v2 ->
        build_vrr_infopacket_fs2_data

Neither mod_freesync_build_vrr_infopacket or build_vrr_infopacket_v2
modify app_tf's value and build_vrr_infopacket_fs2_data expects just
the value so we can avoid dereferencing anything by just passing in
app_tf's value to mod_freesync_build_vrr_infopacket and
build_vrr_infopacket_v2.

There is no functional change because build_vrr_infopacket_fs2_data
doesn't do anything if TRANSFER_FUNC_UNKNOWN is passed to it, the same
as not calling build_vrr_infopacket_fs2_data at all like before this
change when NULL was used for app_tf.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 1544ed3f1747..945e845f3358 100644
--- a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
+++ b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
@@ -656,7 +656,7 @@ 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,
+		enum color_transfer_func app_tf,
 		struct dc_info_packet *infopacket)
 {
 	unsigned int payload_size = 0;
@@ -664,8 +664,7 @@ 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);
 
@@ -676,7 +675,7 @@ 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,
+		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 949a8b62aa98..063af6258fd9 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,
+		enum color_transfer_func app_tf,
 		struct dc_info_packet *infopacket);
 
 void mod_freesync_build_vrr_params(struct mod_freesync *mod_freesync,
-- 
2.19.1

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