linux-kernel - [PATCH] drm/scheduler: Simplify spsc_queue_count check in drm_sched_entity_select

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Date:   Mon,  1 Oct 2018 23:41:24 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     David Airlie <airlied@...ux.ie>
Cc:     dri-devel@...ts.freedesktop.org,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] drm/scheduler: Simplify spsc_queue_count check in drm_sched_entity_select_rq

Clang generates a warning when it sees a logical not followed by a
conditional operator like ==, >, or <.

drivers/gpu/drm/scheduler/sched_entity.c:470:6: warning: logical not is
only applied to the left hand side of this comparison
[-Wlogical-not-parentheses]
        if (!spsc_queue_count(&entity->job_queue) == 0 ||
            ^                                     ~~
drivers/gpu/drm/scheduler/sched_entity.c:470:6: note: add parentheses
after the '!' to evaluate the comparison first
        if (!spsc_queue_count(&entity->job_queue) == 0 ||
            ^
             (                                        )
drivers/gpu/drm/scheduler/sched_entity.c:470:6: note: add parentheses
around left hand side expression to silence this warning
        if (!spsc_queue_count(&entity->job_queue) == 0 ||
            ^
            (                                    )
1 warning generated.

It assumes the author might have made a mistake in their logic:

if (!a == b) -> if (!(a == b))

Sometimes that is the case; other times, it's just a super convoluted
way of saying 'if (a)' when b = 0:

if (!1 == 0) -> if (0 == 0) -> if (true)

Alternatively:

if (!1 == 0) -> if (!!1) -> if (1)

Simplify this comparison so that Clang doesn't complain.

Fixes: 35e160e781a0 ("drm/scheduler: change entities rq even earlier")
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
---
 drivers/gpu/drm/scheduler/sched_entity.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index 4e5e95c0cab5..3e22a54a99c2 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -467,8 +467,7 @@ void drm_sched_entity_select_rq(struct drm_sched_entity *entity)
 	struct dma_fence *fence;
 	struct drm_sched_rq *rq;
 
-	if (!spsc_queue_count(&entity->job_queue) == 0 ||
-	    entity->num_rq_list <= 1)
+	if (spsc_queue_count(&entity->job_queue) || entity->num_rq_list <= 1)
 		return;
 
 	fence = READ_ONCE(entity->last_scheduled);
-- 
2.19.0