[Intel-gfx] [PATCH v8] drm/i915/dsc: Add Per connector debugfs node for DSC support/enable

[Chris Wilson]

Quoting Manasi Navare (2018-12-06 00:54:07)
> DSC can be supported per DP connector. This patch adds a per connector
> debugfs node to expose DSC support capability by the kernel.
> The same node can be used from userspace to force DSC enable.

So this has a nice deadlock that is killing icl sporadically...

> +static int i915_dsc_fec_support_show(struct seq_file *m, void *data)
> +{
> +       struct drm_connector *connector = m->private;
> +       struct drm_device *dev = connector->dev;
> +       struct drm_crtc *crtc;
> +       struct intel_dp *intel_dp;
> +       struct drm_modeset_acquire_ctx ctx;
> +       struct intel_crtc_state *crtc_state = NULL;
> +       int ret = 0;
> +       bool try_again = false;
> +
> +       drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
> +
> +       do {
> +               ret = drm_modeset_lock(&dev->mode_config.connection_mutex,
> +                                      &ctx);
> +               if (ret) {
> +                       ret = -EINTR;
> +                       break;
> +               }
> +               crtc = connector->state->crtc;
> +               if (connector->status != connector_status_connected || !crtc) {
> +                       ret = -ENODEV;
> +                       break;
> +               }
> +               ret = drm_modeset_lock(&crtc->mutex, &ctx);
> +               if (ret == -EDEADLK) {
> +                       ret = drm_modeset_backoff(&ctx);
> +                       if (!ret) {
> +                               try_again = true;

try_again is never cleared on the next loop, so after you hit the
backoff, we never escape on success.

Reported-by: Tomi Sarvela <tomi.p.sarvela at intel.com>
-Chris