On Wed, May 31, 2017 at 05:42:36PM +0200, Maarten Lankhorst wrote:
> On some systems there can be a race condition in which no crtc state is
> added to the first atomic commit. This results in all crtc's having a
> null DDB allocation, causing a FIFO underrun on any update until the
> first modeset.
>
> Changes since v1:
> - Do not take the connection_mutex, this is already done below.
>
> Reported-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Inspired-by: Mahesh Kumar <mahesh1.kumar@xxxxxxxxx>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Fixes: 98d39494d375 ("drm/i915/gen9: Compute DDB allocation at atomic
> check time (v4)")
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.8+
> Cc: Mahesh Kumar <mahesh1.kumar@xxxxxxxxx>
> Cc: Matt Roper <matthew.d.roper@xxxxxxxxx>
Reviewed-by: Matt Roper <matthew.d.roper@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_pm.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 936eef1634c7..fce4bc5ccc99 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4819,11 +4819,19 @@ skl_compute_wm(struct drm_atomic_state *state)
> struct drm_crtc_state *cstate;
> struct intel_atomic_state *intel_state = to_intel_atomic_state(state);
> struct skl_wm_values *results = &intel_state->wm_results;
> + struct drm_device *dev = state->dev;
> struct skl_pipe_wm *pipe_wm;
> bool changed = false;
> int ret, i;
>
> /*
> + * When we distrust bios wm we always need to recompute to set the
> + * expected DDB allocations for each CRTC.
> + */
> + if (to_i915(dev)->wm.distrust_bios_wm)
> + changed = true;
> +
> + /*
> * If this transaction isn't actually touching any CRTC's, don't
> * bother with watermark calculation. Note that if we pass this
> * test, we're guaranteed to hold at least one CRTC state mutex,
> @@ -4833,6 +4841,7 @@ skl_compute_wm(struct drm_atomic_state *state)
> */
> for_each_new_crtc_in_state(state, crtc, cstate, i)
> changed = true;
> +
> if (!changed)
> return 0;
>
> --
> 2.11.0
>
--
Matt Roper
Graphics Software Engineer
IoTG Platform Enabling & Development
Intel Corporation
(916) 356-2795