Add documentation around vkms_output and its initialization.

Signed-off-by: Louis Chauvet <louis.chauvet@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
+ *
  * @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
+ *
+ * @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:
+ * @composer_workq: Ordered workqueue for composer_work
+ * @lock: Lock used to project concurrent acces to the composer
+ * @composer_enabled: Protected by @lock.
+ * @composer_state:
+ * @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.
+ */
 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;
@@ -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
+ * @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 possible_crtc_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 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.
+	 * 1 here designate the first registered CRTC, the one allocated in [1]
+	 */
 	encoder->possible_crtcs = 1;
 
 	ret = drm_connector_attach_encoder(connector, encoder);

-- 
2.44.2

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@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);

Le 19/08/24 - 17:07, José Expósito a écrit :
> 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@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:

This is fixed by [1], but I can move this patch here.

[1]: https://lore.kernel.org/all/20240802-yuv-v9-3-08a706669e16@bootlin.com/
 
> - * 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.

This comment was mainly for me to understand why there is this =1. 
I will change it to =BIT(0) for clarity, but keep the comment as it is not 
obvious why this value is hardcoded.

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

Hi Louis,

I'd make this patch more incremental. First, send me a patch based on
drm-misc-next with the new documentation for the things that already
exists. Then, when you add a new field, you add the documentation with
it.

On 8/14/24 05:47, Louis Chauvet wrote:
> Add documentation around vkms_output and its initialization.
> 
> Signed-off-by: Louis Chauvet <louis.chauvet@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
> + *
>    * @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.

Apart from being protected by @vkms_output.composer_lock, what those
variables represent?

>    */
>   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

s/crtc/CRTC and s/drm/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:

Empty?

> + * @composer_workq: Ordered workqueue for composer_work

Add reference to composer_work

> + * @lock: Lock used to project concurrent acces to the composer

s/acces/access

> + * @composer_enabled: Protected by @lock.
> + * @composer_state:

Empty?

> + * @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/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
> + *
> + * @drm - Base device in drm

s/drm/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;
> @@ -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
> + * @dev: drm_device associated with the vkms buffer

DRM device

> + * @crtc: uninitialized crtc device
> + * @primary: primary plane to attach to the crtc
> + * @cursor plane to attach to the crtc

s/crtc/CRTC everywhere

> + */

New line

>   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.
> + */
>   

Delete line

>   int vkms_output_init(struct vkms_device *vkmsdev, int possible_crtc_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

s/crtc/CRTC everywhere

> + * 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 */

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

Where is [1]?

Best Regards,
- Maíra

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