On Thu, Dec 15, 2016 at 05:13:37PM +0100, Maarten Lankhorst wrote:
> Op 15-12-16 om 16:47 schreef Ville Syrjälä:
> > On Thu, Dec 15, 2016 at 04:34:58PM +0100, Maarten Lankhorst wrote:
> >> Op 12-12-16 om 21:35 schreef ville.syrjala@xxxxxxxxxxxxxxx:
> >>> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> >>>
> >>> On VLV/CHV enabling sprite0 when sprite1 has already been enabled may
> >>> lead to an underrun. This only happens when sprite0 FIFO size is zero
> >>> prior to enabling it. Hence an effective workaround is to always
> >>> allocate at least one cacheline for sprite0 when sprite1 is active.
> >>>
> >>> I've not observed this sort of failure during any other type of plane
> >>> enable/disable sequence.
> >>>
> >>> Testcase: igt/kms_plane_blinker
> >>> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> >>> ---
> >>> drivers/gpu/drm/i915/intel_pm.c | 24 +++++++++++++++++++++++-
> >>> 1 file changed, 23 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> >>> index fa882cdcac52..75a5bde43723 100644
> >>> --- a/drivers/gpu/drm/i915/intel_pm.c
> >>> +++ b/drivers/gpu/drm/i915/intel_pm.c
> >>> @@ -1006,6 +1006,12 @@ static uint16_t vlv_compute_wm_level(const struct intel_crtc_state *crtc_state,
> >>> return min_t(int, wm, USHRT_MAX);
> >>> }
> >>>
> >>> +static bool vlv_need_sprite0_fifo_workaround(unsigned int active_planes)
> >>> +{
> >>> + return (active_planes & (BIT(PLANE_SPRITE0) |
> >>> + BIT(PLANE_SPRITE1))) == BIT(PLANE_SPRITE1);
> >>> +}
> >>> +
> >>> static int vlv_compute_fifo(struct intel_crtc_state *crtc_state)
> >>> {
> >>> struct intel_crtc *crtc = to_intel_crtc(crtc_state->base.crtc);
> >>> @@ -1016,12 +1022,25 @@ static int vlv_compute_fifo(struct intel_crtc_state *crtc_state)
> >>> int num_active_planes = hweight32(active_planes);
> >>> const int fifo_size = 511;
> >>> int fifo_extra, fifo_left = fifo_size;
> >>> + int sprite0_fifo_extra = 0;
> >>> unsigned int total_rate;
> >>> enum plane_id plane_id;
> >>>
> >>> + /*
> >>> + * When enabling sprite0 after sprite1 has already been enabled
> >>> + * we tend to get an underrun unless sprite0 already has some
> >>> + * FIFO space allcoated. Hence we always allocate at least one
> >>> + * cacheline for sprite0 whenever sprite1 is enabled.
> >>> + *
> >>> + * All other plane enable sequences appear immune to this problem.
> >>> + */
> >>> + if (vlv_need_sprite0_fifo_workaround(active_planes))
> >>> + sprite0_fifo_extra = 1;
> >> I don't think you need crtc_state->active_planes just for this, it adds a lot of tracking for something that could be done by
> >>
> >> if (noninverted->plane[SPRITE1] && !noninverted->plane[SPRITE0])
> >> /* allocate 1 for sprite 0 */
> >>
> >> Maybe drop that patch?
> > We'll want it for other things outside of the vlv watermark code as
> > well. So figured this is a good excuse for getting the ball rolling,
> I haven't seen a good reason yet, at least not one that requires visible_mask = BIT(plane->id)
There are a lot of good reasons for tracking active planes: IPS and gen2
fifo underrun suppression come to mind immediately.
--
Ville Syrjälä
Intel OTC
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