drm/vc4: crtc: Reduce PV fifo threshold on hvs4

Experimentally have found PV on hvs4 reports fifo full
error with expected settings and does not with one less

This appears as:
[drm:drm_atomic_helper_wait_for_flip_done] *ERROR* [CRTC:82:crtc-3] flip_done timed out

with bit 10 of PV_STAT set "HVS driving pixels when the PV FIFO is full"

Fixes: c8b75bca92cb ("drm/vc4: Add KMS support for Raspberry Pi.")
Signed-off-by: Dom Cobley <popcornmix@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20210318161328.1471556-3-maxime@cerno.tech

diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4_crtc.c
index 269390b..76657dc 100644 (file)
--- a/drivers/gpu/drm/vc4/vc4_crtc.c
+++ b/drivers/gpu/drm/vc4/vc4_crtc.c
@@ -210,6 +210,7 @@ static u32 vc4_get_fifo_full_level(struct vc4_crtc *vc4_crtc, u32 format)
 {
        const struct vc4_crtc_data *crtc_data = vc4_crtc_to_vc4_crtc_data(vc4_crtc);
        const struct vc4_pv_data *pv_data = vc4_crtc_to_vc4_pv_data(vc4_crtc);
+       struct vc4_dev *vc4 = to_vc4_dev(vc4_crtc->base.dev);
        u32 fifo_len_bytes = pv_data->fifo_depth;
 
        /*
@@ -238,6 +239,22 @@ static u32 vc4_get_fifo_full_level(struct vc4_crtc *vc4_crtc, u32 format)
                if (crtc_data->hvs_output == 5)
                        return 32;
 
+               /*
+                * It looks like in some situations, we will overflow
+                * the PixelValve FIFO (with the bit 10 of PV stat being
+                * set) and stall the HVS / PV, eventually resulting in
+                * a page flip timeout.
+                *
+                * Displaying the video overlay during a playback with
+                * Kodi on an RPi3 seems to be a great solution with a
+                * failure rate around 50%.
+                *
+                * Removing 1 from the FIFO full level however
+                * seems to completely remove that issue.
+                */
+               if (!vc4->hvs->hvs5)
+                       return fifo_len_bytes - 3 * HVS_FIFO_LATENCY_PIX - 1;
+
                return fifo_len_bytes - 3 * HVS_FIFO_LATENCY_PIX;
        }
 }