Re: [PATCH v5 2/3] drm/atomic-helper: Implement subsystem-level suspend/resume

[Matt Roper <matthew.d.roper@intel.com>]

On Wed, Dec 02, 2015 at 05:50:04PM +0100, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
> 
> Provide subsystem-level suspend and resume helpers that can be used to
> implement suspend/resume on atomic mode-setting enabled drivers.
> 
> v2: simplify locking, enhance kerneldoc comments
> v3: pass lock acquisition context by parameter, improve kerneldoc
> v4: - remove redundant code (already provided by atomic helpers)
>       (Maarten Lankhorst)
>     - move backoff dance from drm_modeset_lock_all_ctx() into suspend
>       helper (Daniel Vetter)
> v5: handle potential EDEADLK from drm_atomic_helper_duplicate_state()
>     and drm_atomic_helper_disable_all() (Daniel Vetter)
> 
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 162 +++++++++++++++++++++++++++++++++++-
>  drivers/gpu/drm/drm_crtc_helper.c   |   6 ++
>  include/drm/drm_atomic_helper.h     |   6 ++
>  3 files changed, 173 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 3731a26979bc..ce2cfef08742 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1818,6 +1818,161 @@ commit:
>  }
>  
>  /**
> + * drm_atomic_helper_disable_all - disable all currently active outputs
> + * @dev: DRM device
> + * @ctx: lock acquisition context
> + *
> + * Loops through all connectors, finding those that aren't turned off and then
> + * turns them off by setting their DPMS mode to OFF and deactivating the CRTC
> + * that they are connected to.
> + *
> + * This is used for example in suspend/resume to disable all currently active
> + * functions when suspending.
> + *
> + * Note that if callers haven't already acquired all modeset locks this might
> + * return -EDEADLK, which must be handled by calling drm_modeset_backoff().
> + *
> + * Returns:
> + * 0 on success or a negative error code on failure.
> + *
> + * See also:
> + * drm_atomic_helper_suspend(), drm_atomic_helper_resume()
> + */
> +int drm_atomic_helper_disable_all(struct drm_device *dev,
> +				  struct drm_modeset_acquire_ctx *ctx)
> +{
> +	struct drm_atomic_state *state;
> +	struct drm_connector *conn;
> +	int err;
> +
> +	state = drm_atomic_state_alloc(dev);
> +	if (!state)
> +		return -ENOMEM;
> +
> +	state->acquire_ctx = ctx;
> +
> +	drm_for_each_connector(conn, dev) {

This iterator will raise a WARN() if the caller isn't already holding
either mode_config->mutex or mode_config->connection_mutex.  Should a
note about that be added to the kerneldoc above where you're talking
about locks?  Ditto for the iterator in
drm_atomic_helper_duplicate_state().


Matt

> +		struct drm_crtc *crtc = conn->state->crtc;
> +		struct drm_crtc_state *crtc_state;
> +
> +		if (!crtc || conn->dpms != DRM_MODE_DPMS_ON)
> +			continue;
> +
> +		crtc_state = drm_atomic_get_crtc_state(state, crtc);
> +		if (IS_ERR(crtc_state)) {
> +			err = PTR_ERR(crtc_state);
> +			goto free;
> +		}
> +
> +		crtc_state->active = false;
> +	}
> +
> +	err = drm_atomic_commit(state);
> +
> +free:
> +	if (err < 0)
> +		drm_atomic_state_free(state);
> +
> +	return err;
> +}
> +EXPORT_SYMBOL(drm_atomic_helper_disable_all);
> +
> +/**
> + * drm_atomic_helper_suspend - subsystem-level suspend helper
> + * @dev: DRM device
> + *
> + * Duplicates the current atomic state, disables all active outputs and then
> + * returns a pointer to the original atomic state to the caller. Drivers can
> + * pass this pointer to the drm_atomic_helper_resume() helper upon resume to
> + * restore the output configuration that was active at the time the system
> + * entered suspend.
> + *
> + * Note that it is potentially unsafe to use this. The atomic state object
> + * returned by this function is assumed to be persistent. Drivers must ensure
> + * that this holds true. Before calling this function, drivers must make sure
> + * to suspend fbdev emulation so that nothing can be using the device.
> + *
> + * Returns:
> + * A pointer to a copy of the state before suspend on success or an ERR_PTR()-
> + * encoded error code on failure. Drivers should store the returned atomic
> + * state object and pass it to the drm_atomic_helper_resume() helper upon
> + * resume.
> + *
> + * See also:
> + * drm_atomic_helper_duplicate_state(), drm_atomic_helper_disable_all(),
> + * drm_atomic_helper_resume()
> + */
> +struct drm_atomic_state *drm_atomic_helper_suspend(struct drm_device *dev)
> +{
> +	struct drm_modeset_acquire_ctx ctx;
> +	struct drm_atomic_state *state;
> +	int err;
> +
> +	drm_modeset_acquire_init(&ctx, 0);
> +
> +retry:
> +	err = drm_modeset_lock_all_ctx(dev, &ctx);
> +	if (err < 0) {
> +		state = ERR_PTR(err);
> +		goto unlock;
> +	}
> +
> +	state = drm_atomic_helper_duplicate_state(dev, &ctx);
> +	if (IS_ERR(state))
> +		goto unlock;
> +
> +	err = drm_atomic_helper_disable_all(dev, &ctx);
> +	if (err < 0) {
> +		drm_atomic_state_free(state);
> +		state = ERR_PTR(err);
> +		goto unlock;
> +	}
> +
> +unlock:
> +	if (PTR_ERR(state) == -EDEADLK) {
> +		drm_modeset_backoff(&ctx);
> +		goto retry;
> +	}
> +
> +	drm_modeset_drop_locks(&ctx);
> +	drm_modeset_acquire_fini(&ctx);
> +	return state;
> +}
> +EXPORT_SYMBOL(drm_atomic_helper_suspend);
> +
> +/**
> + * drm_atomic_helper_resume - subsystem-level resume helper
> + * @dev: DRM device
> + * @state: atomic state to resume to
> + *
> + * Calls drm_mode_config_reset() to synchronize hardware and software states,
> + * grabs all modeset locks and commits the atomic state object. This can be
> + * used in conjunction with the drm_atomic_helper_suspend() helper to
> + * implement suspend/resume for drivers that support atomic mode-setting.
> + *
> + * Returns:
> + * 0 on success or a negative error code on failure.
> + *
> + * See also:
> + * drm_atomic_helper_suspend()
> + */
> +int drm_atomic_helper_resume(struct drm_device *dev,
> +			     struct drm_atomic_state *state)
> +{
> +	struct drm_mode_config *config = &dev->mode_config;
> +	int err;
> +
> +	drm_mode_config_reset(dev);
> +	drm_modeset_lock_all(dev);
> +	state->acquire_ctx = config->acquire_ctx;
> +	err = drm_atomic_commit(state);
> +	drm_modeset_unlock_all(dev);
> +
> +	return err;
> +}
> +EXPORT_SYMBOL(drm_atomic_helper_resume);
> +
> +/**
>   * drm_atomic_helper_crtc_set_property - helper for crtc properties
>   * @crtc: DRM crtc
>   * @property: DRM property
> @@ -2429,7 +2584,9 @@ EXPORT_SYMBOL(drm_atomic_helper_connector_duplicate_state);
>   * @ctx: lock acquisition context
>   *
>   * Makes a copy of the current atomic state by looping over all objects and
> - * duplicating their respective states.
> + * duplicating their respective states. This is used for example by suspend/
> + * resume support code to save the state prior to suspend such that it can
> + * be restored upon resume.
>   *
>   * Note that this treats atomic state as persistent between save and restore.
>   * Drivers must make sure that this is possible and won't result in confusion
> @@ -2441,6 +2598,9 @@ EXPORT_SYMBOL(drm_atomic_helper_connector_duplicate_state);
>   * Returns:
>   * A pointer to the copy of the atomic state object on success or an
>   * ERR_PTR()-encoded error code on failure.
> + *
> + * See also:
> + * drm_atomic_helper_suspend(), drm_atomic_helper_resume()
>   */
>  struct drm_atomic_state *
>  drm_atomic_helper_duplicate_state(struct drm_device *dev,
> diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
> index 6b4cf25fed12..10d0989db273 100644
> --- a/drivers/gpu/drm/drm_crtc_helper.c
> +++ b/drivers/gpu/drm/drm_crtc_helper.c
> @@ -855,6 +855,12 @@ EXPORT_SYMBOL(drm_helper_mode_fill_fb_struct);
>   * due to slight differences in allocating shared resources when the
>   * configuration is restored in a different order than when userspace set it up)
>   * need to use their own restore logic.
> + *
> + * This function is deprecated. New drivers should implement atomic mode-
> + * setting and use the atomic suspend/resume helpers.
> + *
> + * See also:
> + * drm_atomic_helper_suspend(), drm_atomic_helper_resume()
>   */
>  void drm_helper_resume_force_mode(struct drm_device *dev)
>  {
> diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
> index 8cba54a2a0a0..8045cdea8cc9 100644
> --- a/include/drm/drm_atomic_helper.h
> +++ b/include/drm/drm_atomic_helper.h
> @@ -81,6 +81,12 @@ int drm_atomic_helper_set_config(struct drm_mode_set *set);
>  int __drm_atomic_helper_set_config(struct drm_mode_set *set,
>  		struct drm_atomic_state *state);
>  
> +int drm_atomic_helper_disable_all(struct drm_device *dev,
> +				  struct drm_modeset_acquire_ctx *ctx);
> +struct drm_atomic_state *drm_atomic_helper_suspend(struct drm_device *dev);
> +int drm_atomic_helper_resume(struct drm_device *dev,
> +			     struct drm_atomic_state *state);
> +
>  int drm_atomic_helper_crtc_set_property(struct drm_crtc *crtc,
>  					struct drm_property *property,
>  					uint64_t val);
> -- 
> 2.5.0
> 

-- 
Matt Roper
Graphics Software Engineer
IoTG Platform Enabling & Development
Intel Corporation
(916) 356-2795
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