Re: [PATCH 04/19] drm/i915: get/put PC8 when we get/put a CRTC

Rodrigo Vivi
2013-11-29T12:38:12Z

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>

On Wed, Nov 27, 2013 at 06:01:19PM -0200, Paulo Zanoni wrote:
> From: Paulo Zanoni <paulo.r.zanoni@intel.com>
>
> Currently, PC8 is enabled at modeset_global_resources, which is called
> after intel_modeset_update_state. Due to this, there's a small race
> condition on the case where we start enabling PC8, then do a modeset
> while PC8 is still being enabled. The racing condition triggers a WARN
> because intel_modeset_update_state will mark the CRTC as enabled, then
> the thread that's still enabling PC8 might look at the data structure
> and think that PC8 is being enabled while a pipe is enabled. Despite
> the WARN, this is not really a bug since we'll wait for the
> PC8-enabling thread to finish when we call modeset_global_resources.
>
> So this patch makes sure we get/put PC8 before we update
> drm_crtc->enabled, because if a get() call triggers a PC8 disable,
> we'll call cancel_delayed_work_sync(), which will wait for the thread
> that's enabling PC8, then, after this, we'll disable PC8.
>
> The side-effect benefit of this patch is that we have a nice place to
> track enabled/disabled CRTCs, so we may want to move some code from
> modeset_global_resources to intel_crtc_set_enabled in the future.
>
> The problem fixed by this patch can be reproduced by the
> modeset-lpsp-stress-no-wait subtest from the pc8 test of
> intel-gpu-tools.
>
> v2: - No need for pc8.lock since we already have
> cancel_delayed_work_sync().
> v3: - Rename to intel_crtc_set_enabled
>
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> ---
> drivers/gpu/drm/i915/intel_display.c | 27 +++++++++++++++++++++++----
> 1 file changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 0eb7053..5adf540 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -9129,6 +9129,24 @@ static bool intel_crtc_in_use(struct drm_crtc *crtc)
> return false;
> }
>
> +/* Sets crtc->base.enabled and gets/puts whatever resources are needed by the
> + * CRTC. */
> +static void intel_crtc_set_enabled(struct intel_crtc *crtc, bool enabled)
> +{
> + struct drm_device *dev = crtc->base.dev;
> + struct drm_i915_private *dev_priv = dev->dev_private;
> +
> + if (enabled == crtc->base.enabled)
> + return;
> +
> + if (enabled)
> + hsw_disable_package_c8(dev_priv);
> + else
> + hsw_enable_package_c8(dev_priv);
> +
> + crtc->base.enabled = enabled;
> +}
> +
> static void
> intel_modeset_update_state(struct drm_device *dev, unsigned prepare_pipes)
> {
> @@ -9152,7 +9170,8 @@ intel_modeset_update_state(struct drm_device *dev, unsigned prepare_pipes)
> /* Update computed state. */
> list_for_each_entry(intel_crtc, &dev->mode_config.crtc_list,
> base.head) {
> - intel_crtc->base.enabled = intel_crtc_in_use(&intel_crtc->base);
> + intel_crtc_set_enabled(intel_crtc,
> + intel_crtc_in_use(&intel_crtc->base));
> }
>
> list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
> @@ -10961,7 +10980,7 @@ static void intel_sanitize_crtc(struct intel_crtc *crtc)
> }
>
> WARN_ON(crtc->active);
> - crtc->base.enabled = false;
> + intel_crtc_set_enabled(crtc, false);
> }
>
> if (dev_priv->quirks & QUIRK_PIPEA_FORCE &&
> @@ -10988,7 +11007,7 @@ static void intel_sanitize_crtc(struct intel_crtc *crtc)
> crtc->base.enabled ? "enabled" : "disabled",
> crtc->active ? "enabled" : "disabled");
>
> - crtc->base.enabled = crtc->active;
> + intel_crtc_set_enabled(crtc, crtc->active);
>
> /* Because we only establish the connector -> encoder ->
> * crtc links if something is active, this means the
> @@ -11085,7 +11104,7 @@ static void intel_modeset_readout_hw_state(struct drm_device *dev)
> crtc->active = dev_priv->display.get_pipe_config(crtc,
> &crtc->config);
>
> - crtc->base.enabled = crtc->active;
> + intel_crtc_set_enabled(crtc, crtc->active);
> crtc->primary_enabled = crtc->active;
>
> DRM_DEBUG_KMS("[CRTC:%d] hw state readout: %s\n",
> --
> 1.8.3.1
>
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