[PATCH v2] drm/vkms: Add documentation

[José Expósito]

Hi Louis,

> Add documentation around vkms_output and its initialization.
> 
> Signed-off-by: Louis Chauvet <louis.chauvet at bootlin.com>
> ---
> This series does not introduce functionnal changes, only some
> documentation and renaming to clarify the code.
> ---
> Changes in v2:
> - Dropped already applied patches
> - Dropped useless patch as its content is deleted later
> - Remove dependency on previous series
> - Apply Maíra's comments
> - Link to v1: https://lore.kernel.org/r/20240814-google-clarifications-v1-0-3ee76d7d0c28@bootlin.com

I think you missed my email in the previous patch:
https://patchwork.kernel.org/project/dri-devel/patch/20240814-google-clarifications-v1-3-3ee76d7d0c28@bootlin.com/#25983103

Minor comments, but it'd be nice to get them fixed if possible.

Jose

> ---
>  drivers/gpu/drm/vkms/vkms_drv.h    | 86 ++++++++++++++++++++++++++++++++------
>  drivers/gpu/drm/vkms/vkms_output.c | 12 ++++++
>  2 files changed, 86 insertions(+), 12 deletions(-)
> 
> 
> ---
> base-commit: 22bc22ccf95bfa6eb6288ba4bc33d7fc0078381e
> change-id: 20240520-google-clarifications-dede8dcbe38a
> 
> Best regards,
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index 5e46ea5b96dc..1fc068d4de4c 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -73,29 +73,56 @@ struct vkms_color_lut {
>  };
>  
>  /**
> - * vkms_crtc_state - Driver specific CRTC state
> + * struct vkms_crtc_state - Driver specific CRTC state
> + *
>   * @base: base CRTC state
>   * @composer_work: work struct to compose and add CRC entries
> - * @n_frame_start: start frame number for computed CRC
> - * @n_frame_end: end frame number for computed CRC
> + *
> + * @num_active_planes: Number of active planes
> + * @active_planes: List containing all the active planes (counted by
> + *  @num_active_planes). They should be stored in z-order.
> + * @active_writeback: Current active writeback job
> + * @gamma_lut: Look up table for gamma used in this CRTC
> + * @crc_pending: Protected by @vkms_output.composer_lock, true when the frame CRC is not computed
> + *		 yet. Used by vblank to detect if the composer is too slow.
> + * @wb_pending: Protected by @vkms_output.composer_lock, true when a writeback frame is requested.
> + * @frame_start: Protected by @vkms_output.composer_lock, saves the frame number before the start
> + *		 of the composition process.
> + * @frame_end: Protected by @vkms_output.composer_lock, saves the last requested frame number.
> + *	       This is used to generate enough CRC entries when the composition worker is too slow.
>   */
>  struct vkms_crtc_state {
>  	struct drm_crtc_state base;
>  	struct work_struct composer_work;
>  
>  	int num_active_planes;
> -	/* stack of active planes for crc computation, should be in z order */
>  	struct vkms_plane_state **active_planes;
>  	struct vkms_writeback_job *active_writeback;
>  	struct vkms_color_lut gamma_lut;
>  
> -	/* below four are protected by vkms_output.composer_lock */
>  	bool crc_pending;
>  	bool wb_pending;
>  	u64 frame_start;
>  	u64 frame_end;
>  };
>  
> +/**
> + * struct vkms_output - Internal representation of all output components in vkms
> + *
> + * @crtc: Base CRTC in DRM
> + * @encoder: DRM encoder used for this output
> + * @connector: DRM connector used for this output
> + * @wb_connecter: DRM writeback connector used for this output
> + * @vblank_hrtimer: Timer used to trigger the vblank
> + * @period_ns: Period of the vblank timer, used to configure @vblank_hrtimer and to compute
> + *	       vblank timestamps
> + * @composer_workq: Ordered workqueue for @composer_state.composer_work.
> + * @lock: Lock used to protect concurrent access to the composer
> + * @composer_enabled: Protected by @lock, true when the vkms composer is active (crc needed or
> + *		      writeback)
> + * @composer_state: Current state of this vkms output
> + * @composer_lock: Lock used internally to protect @composer_state members
> + */
>  struct vkms_output {
>  	struct drm_crtc crtc;
>  	struct drm_encoder encoder;
> @@ -103,28 +130,38 @@ struct vkms_output {
>  	struct drm_writeback_connector wb_connector;
>  	struct hrtimer vblank_hrtimer;
>  	ktime_t period_ns;
> -	/* ordered wq for composer_work */
>  	struct workqueue_struct *composer_workq;
> -	/* protects concurrent access to composer */
>  	spinlock_t lock;
>  
> -	/* protected by @lock */
>  	bool composer_enabled;
>  	struct vkms_crtc_state *composer_state;
>  
>  	spinlock_t composer_lock;
>  };
>  
> -struct vkms_device;
> -
> +/**
> + * struct vkms_config - General configuration for VKMS driver
> + *
> + * @writeback: If true, a writeback buffer can be attached to the CRTC
> + * @cursor: If true, a cursor plane is created in the VKMS device
> + * @overlay: If true, NUM_OVERLAY_PLANES will be created for the VKMS device
> + * @dev: Used to store the current vkms device. Only set when the device is instantiated.
> + */
>  struct vkms_config {
>  	bool writeback;
>  	bool cursor;
>  	bool overlay;
> -	/* only set when instantiated */
>  	struct vkms_device *dev;
>  };
>  
> +/**
> + * struct vkms_device - Description of a vkms device
> + *
> + * @drm - Base device in DRM
> + * @platform - Associated platform device
> + * @output - Configuration and sub-components of the vkms device
> + * @config: Configuration used in this vkms device
> + */
>  struct vkms_device {
>  	struct drm_device drm;
>  	struct platform_device *platform;
> @@ -132,6 +169,10 @@ struct vkms_device {
>  	const struct vkms_config *config;
>  };
>  
> +/*
> + * The following helpers are used to convert a member of a struct into its parent.
> + */
> +
>  #define drm_crtc_to_vkms_output(target) \
>  	container_of(target, struct vkms_output, crtc)
>  
> @@ -144,12 +185,33 @@ struct vkms_device {
>  #define to_vkms_plane_state(target)\
>  	container_of(target, struct vkms_plane_state, base.base)
>  
> -/* CRTC */
> +/**
> + * vkms_crtc_init() - Initialize a CRTC for vkms
> + * @dev: DRM device associated with the vkms buffer
> + * @crtc: uninitialized CRTC device
> + * @primary: primary plane to attach to the CRTC
> + * @cursor plane to attach to the CRTC
> + */
>  int vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
>  		   struct drm_plane *primary, struct drm_plane *cursor);
>  
> +/**
> + * vkms_output_init() - Initialize all sub-components needed for a vkms device.
> + *
> + * @vkmsdev: vkms device to initialize
> + * @possible_crtc_index: CRTC which can be attached to the planes. The caller must ensure that
> + * possible_crtc_index is positive and less or equals to 31.
> + */
>  int vkms_output_init(struct vkms_device *vkmsdev, int index);
>  
> +/**
> + * vkms_plane_init() - Initialize a plane
> + *
> + * @vkmsdev: vkms device containing the plane
> + * @type: type of plane to initialize
> + * @possible_crtc_index: CRTC which can be attached to the plane. The caller must ensure that
> + * possible_crtc_index is positive and less or equals to 31.
> + */
>  struct vkms_plane *vkms_plane_init(struct vkms_device *vkmsdev,
>  				   enum drm_plane_type type, int index);
>  
> diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
> index 5ce70dd946aa..da69beb43ab0 100644
> --- a/drivers/gpu/drm/vkms/vkms_output.c
> +++ b/drivers/gpu/drm/vkms/vkms_output.c
> @@ -21,6 +21,7 @@ static int vkms_conn_get_modes(struct drm_connector *connector)
>  {
>  	int count;
>  
> +	/* Use the default modes list from DRM */
>  	count = drm_add_modes_noedid(connector, XRES_MAX, YRES_MAX);
>  	drm_set_preferred_mode(connector, XRES_DEF, YRES_DEF);
>  
> @@ -58,6 +59,12 @@ int vkms_output_init(struct vkms_device *vkmsdev, int index)
>  	int writeback;
>  	unsigned int n;
>  
> +	/*
> +	 * Initialize used plane. One primary plane is required to perform the composition.
> +	 *
> +	 * The overlay and cursor planes are not mandatory, but can be used to perform complex
> +	 * composition.
> +	 */
>  	primary = vkms_plane_init(vkmsdev, DRM_PLANE_TYPE_PRIMARY, index);
>  	if (IS_ERR(primary))
>  		return PTR_ERR(primary);
> @@ -76,6 +83,7 @@ int vkms_output_init(struct vkms_device *vkmsdev, int index)
>  			return PTR_ERR(cursor);
>  	}
>  
> +	/* [1]: Allocation of a CRTC, its index will be 1 */
>  	ret = vkms_crtc_init(dev, crtc, &primary->base, &cursor->base);
>  	if (ret)
>  		return ret;
> @@ -95,6 +103,10 @@ int vkms_output_init(struct vkms_device *vkmsdev, int index)
>  		DRM_ERROR("Failed to init encoder\n");
>  		goto err_encoder;
>  	}
> +	/*
> +	 * This is an hardcoded value to select crtc for the encoder.
> +	 * 1 here designate the first registered CRTC, the one allocated in [1]
> +	 */
>  	encoder->possible_crtcs = 1;
>  
>  	ret = drm_connector_attach_encoder(connector, encoder);