[PATCH 3/3] drm/vkms: Add documentation

[José Expósito]

Hi Louis,

Thanks for this patch, adding some minor review comments:

> Add documentation around vkms_output and its initialization.
> 
> Signed-off-by: Louis Chauvet <louis.chauvet at bootlin.com>
> ---
>  drivers/gpu/drm/vkms/vkms_drv.h    | 81 ++++++++++++++++++++++++++++++++------
>  drivers/gpu/drm/vkms/vkms_output.c | 12 +++++-
>  2 files changed, 80 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index 3028678e4f9b..8f6c9e67e671 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -147,29 +147,51 @@ struct vkms_color_lut {
>  };
>  
>  /**
> - * vkms_crtc_state - Driver specific CRTC state
> + * struct vkms_crtc_state - Driver specific CRTC state

Not in this line, but around line 55, the documentation for vkms_plane_state
is missing the "struct" keyword:

- * vkms_plane_state - Driver specific plane state
+ * struct vkms_plane_state - Driver specific plane state

I'd be nice to add it since we are improving the documentation.

> + *
>   * @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.
> + * @wb_pending: Protected by @vkms_output.composer_lock.
> + * @frame_start: Protected by @vkms_output.composer_lock.
> + * @frame_end: Protected by @vkms_output.composer_lock.
>   */
>  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

I think that VKMS is usually spelled in capital letters in other places.

> + *
> + * @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:
> + * @period_ns:

My suggestion when reviewing a previous version of this patch in your
GitHub fork was:

 @vblank_hrtimer: Timer used to simulate vblank events
 @period_ns: vblank period, in nanoseconds

> + * @composer_workq: Ordered workqueue for composer_work
> + * @lock: Lock used to project concurrent acces to the composer
> + * @composer_enabled: Protected by @lock.
> + * @composer_state:

I think that @composer_state is "Protected by @lock" as well.

> + * @composer_lock: Lock used internally to protect @composer_state members
> + */
>  struct vkms_output {
>  	struct drm_crtc crtc;
>  	struct drm_encoder encoder;
> @@ -177,28 +199,38 @@ 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 instancied.

s/vkms/VKMS and s/instancied/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

s/vkms/VKMS

> + *
> + * @drm - Base device in drm
> + * @platform - Associated platform device
> + * @output - Configuration and sub-components of the vkms device

s/vkms/VKMS

> + * @config: Configuration used in this vkms device

s/vkms/VKMS

> + */
>  struct vkms_device {
>  	struct drm_device drm;
>  	struct platform_device *platform;
> @@ -206,6 +238,10 @@ 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)
>  
> @@ -218,12 +254,33 @@ 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

s/vkms/VKMS

> + * @dev: drm_device associated with the vkms buffer

s/vkms/VKMS

> + * @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.

s/vkms/VKMS

> + *
> + * @vkmsdev: vkms device to initialize

s/vkms/VKMS

> + * @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.

Missing "@". Also, since the second patch of this series won't be applied,
remember to rename the documentation to "@index".
> + */
>  
>  int vkms_output_init(struct vkms_device *vkmsdev, int possible_crtc_index);
>  
> +/**
> + * vkms_plane_init() - Initialize a plane
> + *
> + * @vkmsdev: vkms device containing the plane

s/vkms/VKMS

> + * @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 possible_crtc_index);
>  
> diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
> index d42ca7d10389..36db2c8923cb 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);
>  
> @@ -58,8 +59,13 @@ int vkms_output_init(struct vkms_device *vkmsdev, int possible_crtc_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, possible_crtc_index);
> -
>  	if (IS_ERR(primary))
>  		return PTR_ERR(primary);
>  
> @@ -96,6 +102,10 @@ int vkms_output_init(struct vkms_device *vkmsdev, int possible_crtc_index)
>  		DRM_ERROR("Failed to init encoder\n");
>  		goto err_encoder;
>  	}
> +	/*
> +	 * This is an hardcoded value to select crtc for the encoder.

s/an/a

> +	 * 1 here designate the first registered CRTC, the one allocated in [1]
> +	 */

I think that replacing "= 1;" with "= BIT(0);" might help to understand
that possible_crtcs is a bitmask and also that CRTC 0 is used by default.
We might even be able to drop the comment... Even though this will change
with our configfs changes quite a lot.

>  	encoder->possible_crtcs = 1;
>  
>  	ret = drm_connector_attach_encoder(connector, encoder);