[PATCH 5/8] drm/rockchip: vop2: Report POST_BUF_EMPTY at most once per frame
Chaoyi Chen
chaoyi.chen at rock-chips.com
Tue Nov 10 02:54:57 PST 2026
Hi Arun,
On 11/10/2026 3:18 PM, Arun Iyengar via B4 Relay wrote:
> From: Arun Iyengar <aiyengar1990 at gmail.com>
>
> POST_BUF_EMPTY is raised for every line on which the post processing
> stage of a video port finds no data. The interrupt handler only
> rate-limits the error message and leaves the interrupt enabled, so an
> underflowing video port keeps the CPU in the interrupt handler 50000 to
> 300000 times per second, for as long as the configuration that causes
> the underflow stays in place (e.g. 120000 interrupts per second for
> 3840x2160 at 120 with two full screen layers on one AXI port).
>
> Mask POST_BUF_EMPTY when it fires and unmask it at the next frame start.
> The frame start (FS) interrupt is enabled for that frame even when
> vblank reporting is off, and disabled again once POST_BUF_EMPTY is
> re-armed. A new per video port lock serialises the interrupt enable
> bookkeeping between the interrupt handler and the vblank callbacks.
> The error is still reported, now at most once per frame and video port.
>
> Signed-off-by: Arun Iyengar <aiyengar1990 at gmail.com>
> ---
> drivers/gpu/drm/rockchip/rockchip_drm_vop2.c | 63 ++++++++++++++++++++++++++--
> drivers/gpu/drm/rockchip/rockchip_drm_vop2.h | 10 +++++
> 2 files changed, 70 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
> index 9aeb90c6aa4b..3323e50224c5 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
> @@ -841,6 +841,48 @@ static void vop2_crtc_disable_irq(struct vop2_video_port *vp, u32 irq)
> vop2_writel(vop2, RK3568_VP_INT_EN(vp->id), irq << 16);
> }
>
> +/*
> + * POST_BUF_EMPTY is raised for every line the post processing stage finds
> + * no data for, so an underflowing video port can raise it 100000 times per
> + * second. Report it at most once per frame: mask it when it fires and
> + * unmask it at the next frame start, using the FS interrupt even when
> + * vblank reporting is off.
> + */
> +static void vop2_crtc_enable_post_buf_empty_irq(struct vop2_video_port *vp)
> +{
> + unsigned long flags;
> +
> + spin_lock_irqsave(&vp->irq_lock, flags);
> + vp->post_buf_empty_masked = false;
> + vop2_crtc_enable_irq(vp, VP_INT_POST_BUF_EMPTY);
> + spin_unlock_irqrestore(&vp->irq_lock, flags);
> +}
> +
> +static void vop2_crtc_handle_post_buf_empty(struct vop2_video_port *vp)
> +{
> + struct vop2 *vop2 = vp->vop2;
> +
> + spin_lock(&vp->irq_lock);
> + vop2_crtc_disable_irq(vp, VP_INT_POST_BUF_EMPTY);
> + vp->post_buf_empty_masked = true;
> + /* don't clear a pending FS, it may carry a vblank event */
> + vop2_writel(vop2, RK3568_VP_INT_EN(vp->id),
> + VP_INT_FS_FIELD << 16 | VP_INT_FS_FIELD);
Do we really need this? Disabling the POST_BUF_EMPTY IRQ should not
affect the FS_FIELD IRQ, because this register has write mask.
> + spin_unlock(&vp->irq_lock);
> +}
> +
> +static void vop2_crtc_rearm_post_buf_empty(struct vop2_video_port *vp)
> +{
> + spin_lock(&vp->irq_lock);
> + if (vp->post_buf_empty_masked) {
> + vp->post_buf_empty_masked = false;
> + vop2_crtc_enable_irq(vp, VP_INT_POST_BUF_EMPTY);
> + if (!vp->vblank_enabled)
> + vop2_crtc_disable_irq(vp, VP_INT_FS_FIELD);
> + }
> + spin_unlock(&vp->irq_lock);
> +}
> +
> static int vop2_core_clks_prepare_enable(struct vop2 *vop2)
> {
> int ret;
> @@ -1668,8 +1710,12 @@ static const struct drm_plane_funcs vop2_plane_funcs = {
> static int vop2_crtc_enable_vblank(struct drm_crtc *crtc)
> {
> struct vop2_video_port *vp = to_vop2_video_port(crtc);
> + unsigned long flags;
>
> + spin_lock_irqsave(&vp->irq_lock, flags);
> + vp->vblank_enabled = true;
> vop2_crtc_enable_irq(vp, VP_INT_FS_FIELD);
> + spin_unlock_irqrestore(&vp->irq_lock, flags);
>
> return 0;
> }
> @@ -1677,8 +1723,13 @@ static int vop2_crtc_enable_vblank(struct drm_crtc *crtc)
> static void vop2_crtc_disable_vblank(struct drm_crtc *crtc)
> {
> struct vop2_video_port *vp = to_vop2_video_port(crtc);
> + unsigned long flags;
>
> - vop2_crtc_disable_irq(vp, VP_INT_FS_FIELD);
> + spin_lock_irqsave(&vp->irq_lock, flags);
> + vp->vblank_enabled = false;
> + if (!vp->post_buf_empty_masked)
> + vop2_crtc_disable_irq(vp, VP_INT_FS_FIELD);
> + spin_unlock_irqrestore(&vp->irq_lock, flags);
> }
>
> static enum drm_mode_status vop2_crtc_mode_valid(struct drm_crtc *crtc,
> @@ -1977,7 +2028,7 @@ static void vop2_crtc_atomic_enable(struct drm_crtc *crtc,
>
> vcstate->yuv_overlay = is_yuv_output(vcstate->bus_format);
>
> - vop2_crtc_enable_irq(vp, VP_INT_POST_BUF_EMPTY);
> + vop2_crtc_enable_post_buf_empty_irq(vp);
>
> polflags = 0;
> if (vcstate->bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE)
> @@ -2535,6 +2586,7 @@ static irqreturn_t rk3576_vp_isr(int irq, void *data)
> }
>
> if (irqs & VP_INT_FS_FIELD) {
> + vop2_crtc_rearm_post_buf_empty(vp);
> drm_crtc_handle_vblank(crtc);
> spin_lock(&crtc->dev->event_lock);
> if (vp->event) {
> @@ -2552,6 +2604,7 @@ static irqreturn_t rk3576_vp_isr(int irq, void *data)
> }
>
> if (irqs & VP_INT_POST_BUF_EMPTY) {
> + vop2_crtc_handle_post_buf_empty(vp);
> drm_err_ratelimited(vop2->drm, "POST_BUF_EMPTY irq err at vp%d\n", vp->id);
> ret = IRQ_HANDLED;
> }
> @@ -2591,6 +2644,7 @@ static irqreturn_t vop2_isr(int irq, void *data)
> }
>
> if (irqs & VP_INT_FS_FIELD) {
> + vop2_crtc_rearm_post_buf_empty(vp);
> drm_crtc_handle_vblank(crtc);
> spin_lock(&crtc->dev->event_lock);
> if (vp->event) {
> @@ -2608,6 +2662,7 @@ static irqreturn_t vop2_isr(int irq, void *data)
> }
>
> if (irqs & VP_INT_POST_BUF_EMPTY) {
> + vop2_crtc_handle_post_buf_empty(vp);
> drm_err_ratelimited(vop2->drm,
> "POST_BUF_EMPTY irq err at vp%d\n",
> vp->id);
> @@ -2984,7 +3039,7 @@ static int vop2_bind(struct device *dev, struct device *master, void *data)
> struct vop2 *vop2;
> struct resource *res;
> size_t alloc_size;
> - int ret;
> + int ret, i;
>
> vop2_data = of_device_get_match_data(dev);
> if (!vop2_data)
> @@ -3102,6 +3157,8 @@ static int vop2_bind(struct device *dev, struct device *master, void *data)
> mutex_init(&vop2->vop2_lock);
> mutex_init(&vop2->ovl_lock);
> spin_lock_init(&vop2->axi_lock);
> + for (i = 0; i < ARRAY_SIZE(vop2->vps); i++)
> + spin_lock_init(&vop2->vps[i].irq_lock);
>
> ret = devm_request_irq(dev, vop2->irq, vop2_isr, IRQF_SHARED, dev_name(dev), vop2);
> if (ret)
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.h b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.h
> index f1e35967e67f..7de32bef8d7b 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.h
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.h
> @@ -272,6 +272,16 @@ struct vop2_video_port {
> struct drm_pending_vblank_event *event;
>
> unsigned int nlayers;
> +
> + /** @irq_lock: protects @vblank_enabled and @post_buf_empty_masked */
> + spinlock_t irq_lock;
> + /** @vblank_enabled: the FS interrupt is enabled for vblank reporting */
> + bool vblank_enabled;
> + /**
> + * @post_buf_empty_masked: POST_BUF_EMPTY is masked until the next
> + * frame start
> + */
> + bool post_buf_empty_masked;
> };
>
> /**
>
--
Best,
Chaoyi
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