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    Subject[PATCH 5.15 771/779] drm/msm: Fix dirtyfb refcounting
    Date
    From: Rob Clark <robdclark@chromium.org>

    commit 9225b337072a10bf9b09df8bf281437488dd8a26 upstream.

    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: 9e4dde28e9cd ("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
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/gpu/drm/msm/msm_fb.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- 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(struc
    /* 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_frame
    goto fail;
    }

    + refcount_set(&msm_fb->dirtyfb, 1);
    +
    drm_dbg_state(dev, "create: FB ID: %d (%p)", fb->base.id, fb);

    return fb;

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