drm/msm: Fix dirtyfb refcounting

refcount_t complains about 0->1 transitions, which isn't *quite* what we
wanted.  So use dirtyfb==1 to mean that the fb is not connected to any
output that requires dirtyfb flushing, so that we can keep the underflow
and overflow checking.

Fixes: ec882c8d0ec6 ("drm/msm: Avoid dirtyfb stalls on video mode displays (v2)")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Link: https://lore.kernel.org/r/20220304202146.845566-1-robdclark@gmail.com

diff --git a/drivers/gpu/drm/msm/msm_fb.c b/drivers/gpu/drm/msm/msm_fb.c
index 96b379a08327c1d4bae0c5571ce017790162fc00..7137492fe78e2890131dfaccd608c6df4e069db7 100644 (file)
--- a/drivers/gpu/drm/msm/msm_fb.c
+++ b/drivers/gpu/drm/msm/msm_fb.c
@@ -37,7 +37,7 @@ static int msm_framebuffer_dirtyfb(struct drm_framebuffer *fb,
        /* If this fb is not used on any display requiring pixel data to be
         * flushed, then skip dirtyfb
         */
-       if (refcount_read(&msm_fb->dirtyfb) == 0)
+       if (refcount_read(&msm_fb->dirtyfb) == 1)
                return 0;
 
        return drm_atomic_helper_dirtyfb(fb, file_priv, flags, color,
@@ -221,6 +221,8 @@ static struct drm_framebuffer *msm_framebuffer_init(struct drm_device *dev,
                goto fail;
        }
 
+       refcount_set(&msm_fb->dirtyfb, 1);
+
        drm_dbg_state(dev, "create: FB ID: %d (%p)", fb->base.id, fb);
 
        return fb;