Re: [PATCH] drm: Add crtc/encoder/bridge->mode_valid() callbacks

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Hi Daniel,


On 12-05-2017 08:31, Daniel Vetter wrote:
> From: Jose Abreu <Jose.Abreu@xxxxxxxxxxxx>
>
> This adds a new callback to crtc, encoder and bridge helper functions
> called mode_valid(). This callback shall be implemented if the
> corresponding component has some sort of restriction in the modes
> that can be displayed. A NULL callback implicates that the component
> can display all the modes.
>
> We also change the documentation so that the new and old callbacks
> are correctly documented.
>
> Only the callbacks were implemented to simplify review process,
> following patches will make use of them.
>
> Changes in v2 from Daniel:
> - Update the warning about how modes aren't filtered in atomic_check -
>   the heleprs help out a lot more now.
> - Consistenly roll out that warning, crtc/encoder's atomic_check
>   missed it.
> - Sprinkle more links all over the place, so it's easier to see where
>   this stuff is used and how the differen hooks are related.
> - Note that ->mode_valid is optional everywhere.
> - Explain why the connector's mode_valid is special and does _not_ get
>   called in atomic_check.
>
> Signed-off-by: Jose Abreu <joabreu@xxxxxxxxxxxx>
> Cc: Jose Abreu <joabreu@xxxxxxxxxxxx>
> Cc: Carlos Palminha <palminha@xxxxxxxxxxxx>
> Cc: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Dave Airlie <airlied@xxxxxxxx>
> Cc: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> Cc: Archit Taneja <architt@xxxxxxxxxxxxxx>
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx> (v2)

Thanks! Looks fine by me.

Reviewed-by: Jose Abreu <joabreu@xxxxxxxxxxxx>

Best regards,
Jose Miguel Abreu

> ---
>  include/drm/drm_bridge.h                 |  31 +++++++++
>  include/drm/drm_modeset_helper_vtables.h | 116 ++++++++++++++++++++++---------
>  2 files changed, 114 insertions(+), 33 deletions(-)
>
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index fdd82fcbf168..f694de756ecf 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -59,6 +59,31 @@ struct drm_bridge_funcs {
>  	void (*detach)(struct drm_bridge *bridge);
>  
>  	/**
> +	 * @mode_valid:
> +	 *
> +	 * This callback is used to check if a specific mode is valid in this
> +	 * bridge. This should be implemented if the bridge has some sort of
> +	 * restriction in the modes it can display. For example, a given bridge
> +	 * may be responsible to set a clock value. If the clock can not
> +	 * produce all the values for the available modes then this callback
> +	 * can be used to restrict the number of modes to only the ones that
> +	 * can be displayed.
> +	 *
> +	 * This hook is used by the probe helpers to filter the mode list in
> +	 * drm_helper_probe_single_connector_modes(), and it is used by the
> +	 * atomic helpers to validate modes supplied by userspace in
> +	 * drm_atomic_helper_check_modeset().
> +	 *
> +	 * This function is optional.
> +	 *
> +	 * RETURNS:
> +	 *
> +	 * drm_mode_status Enum
> +	 */
> +	enum drm_mode_status (*mode_valid)(struct drm_bridge *crtc,
> +					   const struct drm_display_mode *mode);
> +
> +	/**
>  	 * @mode_fixup:
>  	 *
>  	 * This callback is used to validate and adjust a mode. The paramater
> @@ -82,6 +107,12 @@ struct drm_bridge_funcs {
>  	 * NOT touch any persistent state (hardware or software) or data
>  	 * structures except the passed in @state parameter.
>  	 *
> +	 * Also beware that userspace can request its own custom modes, neither
> +	 * core nor helpers filter modes to the list of probe modes reported by
> +	 * the GETCONNECTOR IOCTL and stored in &drm_connector.modes. To ensure
> +	 * that modes are filtered consistently put any bridge constraints and
> +	 * limits checks into @mode_valid.
> +	 *
>  	 * RETURNS:
>  	 *
>  	 * True if an acceptable configuration is possible, false if the modeset
> diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
> index c01c328f6cc8..91d071ff1232 100644
> --- a/include/drm/drm_modeset_helper_vtables.h
> +++ b/include/drm/drm_modeset_helper_vtables.h
> @@ -106,6 +106,31 @@ struct drm_crtc_helper_funcs {
>  	void (*commit)(struct drm_crtc *crtc);
>  
>  	/**
> +	 * @mode_valid:
> +	 *
> +	 * This callback is used to check if a specific mode is valid in this
> +	 * crtc. This should be implemented if the crtc has some sort of
> +	 * restriction in the modes it can display. For example, a given crtc
> +	 * may be responsible to set a clock value. If the clock can not
> +	 * produce all the values for the available modes then this callback
> +	 * can be used to restrict the number of modes to only the ones that
> +	 * can be displayed.
> +	 *
> +	 * This hook is used by the probe helpers to filter the mode list in
> +	 * drm_helper_probe_single_connector_modes(), and it is used by the
> +	 * atomic helpers to validate modes supplied by userspace in
> +	 * drm_atomic_helper_check_modeset().
> +	 *
> +	 * This function is optional.
> +	 *
> +	 * RETURNS:
> +	 *
> +	 * drm_mode_status Enum
> +	 */
> +	enum drm_mode_status (*mode_valid)(struct drm_crtc *crtc,
> +					   const struct drm_display_mode *mode);
> +
> +	/**
>  	 * @mode_fixup:
>  	 *
>  	 * This callback is used to validate a mode. The parameter mode is the
> @@ -132,20 +157,11 @@ struct drm_crtc_helper_funcs {
>  	 * Atomic drivers which need to inspect and adjust more state should
>  	 * instead use the @atomic_check callback.
>  	 *
> -	 * Also beware that neither core nor helpers filter modes before
> -	 * passing them to the driver: While the list of modes that is
> -	 * advertised to userspace is filtered using the
> -	 * &drm_connector.mode_valid callback, neither the core nor the helpers
> -	 * do any filtering on modes passed in from userspace when setting a
> -	 * mode. It is therefore possible for userspace to pass in a mode that
> -	 * was previously filtered out using &drm_connector.mode_valid or add a
> -	 * custom mode that wasn't probed from EDID or similar to begin with.
> -	 * Even though this is an advanced feature and rarely used nowadays,
> -	 * some users rely on being able to specify modes manually so drivers
> -	 * must be prepared to deal with it. Specifically this means that all
> -	 * drivers need not only validate modes in &drm_connector.mode_valid but
> -	 * also in this or in the &drm_encoder_helper_funcs.mode_fixup callback
> -	 * to make sure invalid modes passed in from userspace are rejected.
> +	 * Also beware that userspace can request its own custom modes, neither
> +	 * core nor helpers filter modes to the list of probe modes reported by
> +	 * the GETCONNECTOR IOCTL and stored in &drm_connector.modes. To ensure
> +	 * that modes are filtered consistently put any CRTC constraints and
> +	 * limits checks into @mode_valid.
>  	 *
>  	 * RETURNS:
>  	 *
> @@ -341,6 +357,12 @@ struct drm_crtc_helper_funcs {
>  	 * state objects passed-in or assembled in the overall &drm_atomic_state
>  	 * update tracking structure.
>  	 *
> +	 * Also beware that userspace can request its own custom modes, neither
> +	 * core nor helpers filter modes to the list of probe modes reported by
> +	 * the GETCONNECTOR IOCTL and stored in &drm_connector.modes. To ensure
> +	 * that modes are filtered consistently put any CRTC constraints and
> +	 * limits checks into @mode_valid.
> +	 *
>  	 * RETURNS:
>  	 *
>  	 * 0 on success, -EINVAL if the state or the transition can't be
> @@ -457,6 +479,31 @@ struct drm_encoder_helper_funcs {
>  	void (*dpms)(struct drm_encoder *encoder, int mode);
>  
>  	/**
> +	 * @mode_valid:
> +	 *
> +	 * This callback is used to check if a specific mode is valid in this
> +	 * encoder. This should be implemented if the encoder has some sort
> +	 * of restriction in the modes it can display. For example, a given
> +	 * encoder may be responsible to set a clock value. If the clock can
> +	 * not produce all the values for the available modes then this callback
> +	 * can be used to restrict the number of modes to only the ones that
> +	 * can be displayed.
> +	 *
> +	 * This hook is used by the probe helpers to filter the mode list in
> +	 * drm_helper_probe_single_connector_modes(), and it is used by the
> +	 * atomic helpers to validate modes supplied by userspace in
> +	 * drm_atomic_helper_check_modeset().
> +	 *
> +	 * This function is optional.
> +	 *
> +	 * RETURNS:
> +	 *
> +	 * drm_mode_status Enum
> +	 */
> +	enum drm_mode_status (*mode_valid)(struct drm_encoder *crtc,
> +					   const struct drm_display_mode *mode);
> +
> +	/**
>  	 * @mode_fixup:
>  	 *
>  	 * This callback is used to validate and adjust a mode. The parameter
> @@ -482,21 +529,11 @@ struct drm_encoder_helper_funcs {
>  	 * Atomic drivers which need to inspect and adjust more state should
>  	 * instead use the @atomic_check callback.
>  	 *
> -	 * Also beware that neither core nor helpers filter modes before
> -	 * passing them to the driver: While the list of modes that is
> -	 * advertised to userspace is filtered using the connector's
> -	 * &drm_connector_helper_funcs.mode_valid callback, neither the core nor
> -	 * the helpers do any filtering on modes passed in from userspace when
> -	 * setting a mode. It is therefore possible for userspace to pass in a
> -	 * mode that was previously filtered out using
> -	 * &drm_connector_helper_funcs.mode_valid or add a custom mode that
> -	 * wasn't probed from EDID or similar to begin with.  Even though this
> -	 * is an advanced feature and rarely used nowadays, some users rely on
> -	 * being able to specify modes manually so drivers must be prepared to
> -	 * deal with it. Specifically this means that all drivers need not only
> -	 * validate modes in &drm_connector.mode_valid but also in this or in
> -	 * the &drm_crtc_helper_funcs.mode_fixup callback to make sure
> -	 * invalid modes passed in from userspace are rejected.
> +	 * Also beware that userspace can request its own custom modes, neither
> +	 * core nor helpers filter modes to the list of probe modes reported by
> +	 * the GETCONNECTOR IOCTL and stored in &drm_connector.modes. To ensure
> +	 * that modes are filtered consistently put any encoder constraints and
> +	 * limits checks into @mode_valid.
>  	 *
>  	 * RETURNS:
>  	 *
> @@ -686,6 +723,12 @@ struct drm_encoder_helper_funcs {
>  	 * state objects passed-in or assembled in the overall &drm_atomic_state
>  	 * update tracking structure.
>  	 *
> +	 * Also beware that userspace can request its own custom modes, neither
> +	 * core nor helpers filter modes to the list of probe modes reported by
> +	 * the GETCONNECTOR IOCTL and stored in &drm_connector.modes. To ensure
> +	 * that modes are filtered consistently put any encoder constraints and
> +	 * limits checks into @mode_valid.
> +	 *
>  	 * RETURNS:
>  	 *
>  	 * 0 on success, -EINVAL if the state or the transition can't be
> @@ -795,13 +838,20 @@ struct drm_connector_helper_funcs {
>  	 * (which is usually derived from the EDID data block from the sink).
>  	 * See e.g. drm_helper_probe_single_connector_modes().
>  	 *
> +	 * This function is optional.
> +	 *
>  	 * NOTE:
>  	 *
>  	 * This only filters the mode list supplied to userspace in the
> -	 * GETCONNECOTR IOCTL. Userspace is free to create modes of its own and
> -	 * ask the kernel to use them. It this case the atomic helpers or legacy
> -	 * CRTC helpers will not call this function. Drivers therefore must
> -	 * still fully validate any mode passed in in a modeset request.
> +	 * GETCONNECTOR IOCTL. Compared to &drm_encoder_helper_funcs.mode_valid,
> +	 * &drm_crtc_helper_funcs.mode_valid and &drm_bridge_funcs.mode_valid,
> +	 * which are also called by the atomic helpers from
> +	 * drm_atomic_helper_check_modeset(). This allows userspace to force and
> +	 * ignore sink constraint (like the pixel clock limits in the screen's
> +	 * EDID), which is useful for e.g. testing, or working around a broken
> +	 * EDID. Any source hardware constraint (which always need to be
> +	 * enforced) therefore should be checked in one of the above callbacks,
> +	 * and not this one here.
>  	 *
>  	 * To avoid races with concurrent connector state updates, the helper
>  	 * libraries always call this with the &drm_mode_config.connection_mutex

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