Message-ID: <ZtmxuPg1U3dOCWXg@louis-chauvet-laptop>
Date: Thu, 5 Sep 2024 15:27:20 +0200
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: José Expósito <jose.exposito89@...il.com>
Cc: airlied@...il.com, arthurgrillo@...eup.net, daniel@...ll.ch,
	dri-devel@...ts.freedesktop.org, hamohammed.sa@...il.com,
	jeremie.dautheribes@...tlin.com, linux-kernel@...r.kernel.org,
	maarten.lankhorst@...ux.intel.com, mairacanal@...eup.net,
	marcheu@...gle.com, melissa.srw@...il.com,
	miquel.raynal@...tlin.com, mripard@...nel.org,
	nicolejadeyee@...gle.com, rodrigosiqueiramelo@...il.com,
	seanpaul@...gle.com, thomas.petazzoni@...tlin.com,
	tzimmermann@...e.de
Subject: Re: [PATCH v3] drm/vkms: Add documentation

Le 05/09/24 - 14:33, José Expósito a écrit :
> Hi Louis,
> 
> Thanks for appling the suggested changes.
> 
> I added some minor style comments, but other than that patch looks
> good to me.
> 
> > Add documentation around vkms_output and its initialization.
> > Add some documentation on pixel conversion functions.
> > Update of outdated comments for pixel_write functions.
> > 
> > Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> 
> With the suggested changes, feel free to add:
> Reviewed-by: José Expósito <jose.exposito89@...il.com>

Thanks, the v4 is in your inbox!
 
> > ---
> > This series does not introduce functionnal changes, only some
> > documentation and renaming to clarify the code.
> > ---
> > Changes in v3:
> > - Merged https://lore.kernel.org/all/20240802-yuv-v9-3-08a706669e16@bootlin.com/
> >   as it also add documentation
> > - Apply José's comments, sorry
> > - Replace =1 by =BIT(0) for possible_crtc value
> > - Link to v2: https://lore.kernel.org/r/20240826-google-clarifications-v2-1-2574655b0b91@bootlin.com
> > 
> > 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
> > ---
> >  drivers/gpu/drm/vkms/vkms_composer.c |   7 +++
> >  drivers/gpu/drm/vkms/vkms_drv.h      | 101 ++++++++++++++++++++++++++++++-----
> >  drivers/gpu/drm/vkms/vkms_formats.c  |  62 +++++++++++++++++----
> >  drivers/gpu/drm/vkms/vkms_output.c   |  14 ++++-
> >  4 files changed, 161 insertions(+), 23 deletions(-)
> > 
> > 
> > ---
> > base-commit: 84addde447fd9d713e101437db0d4924855eff4f
> > change-id: 20240520-google-clarifications-dede8dcbe38a
> > 
> > Best regards,
> > 
> > diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> > index e7441b227b3c..57a5769fc994 100644
> > --- a/drivers/gpu/drm/vkms/vkms_composer.c
> > +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> > @@ -189,6 +189,13 @@ static void blend(struct vkms_writeback_job *wb,
> >  
> >  	size_t crtc_y_limit = crtc_state->base.crtc->mode.vdisplay;
> >  
> > +	/*
> > +	 * The planes are composed line-by-line to avoid heavy memory usage. It is a necessary
> > +	 * complexity to avoid poor blending performance.
> > +	 *
> > +	 * The function vkms_compose_row() is used to read a line, pixel-by-pixel, into the staging
> > +	 * buffer.
> > +	 */
> >  	for (size_t y = 0; y < crtc_y_limit; y++) {
> >  		fill_background(&background_color, output_buffer);
> >  
> > diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> > index 5e46ea5b96dc..12a11976f2fc 100644
> > --- a/drivers/gpu/drm/vkms/vkms_drv.h
> > +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> > @@ -25,6 +25,17 @@
> >  
> >  #define VKMS_LUT_SIZE 256
> >  
> > +/**
> > + * struct vkms_frame_info - Structure to store the state of a frame
> > + *
> > + * @fb: backing drm framebuffer
> > + * @src: source rectangle of this frame in the source framebuffer, stored in 16.16 fixed-point form
> > + * @dst: destination rectangle in the crtc buffer, stored in whole pixel units
> > + * @map: see drm_shadow_plane_state@...a
> 
> I think that the right format is "@drm_shadow_plane_state.data"?
> https://docs.kernel.org/doc-guide/kernel-doc.html#nested-structs-unions
> 
> > + * @rotation: rotation applied to the source.
> > + *
> > + * @src and @dst should have the same size modulo the rotation.
> > + */
> >  struct vkms_frame_info {
> >  	struct drm_framebuffer *fb;
> >  	struct drm_rect src, dst;
> > @@ -52,9 +63,11 @@ struct vkms_writeback_job {
> >  };
> >  
> >  /**
> > - * vkms_plane_state - Driver specific plane state
> > + * struct vkms_plane_state - Driver specific plane state
> >   * @base: base plane state
> >   * @frame_info: data required for composing computation
> > + * @pixel_read: function to read a pixel in this plane. The creator of a struct vkms_plane_state
> > + *	        must ensure that this pointer is valid
> >   */
> >  struct vkms_plane_state {
> >  	struct drm_shadow_plane_state base;
> > @@ -73,29 +86,56 @@ 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
> > + *
> 
> Sorry I missed this extra empty line in my previous review.
> You can delete this extra "*".
> 
> > + * @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: vblank period, in nanoseconds, 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: Protected by @lock, 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 +143,38 @@ 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 +182,10 @@ 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 +198,33 @@ 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
> 
> Missing ":" after "@cursor":
> 
>  * @cursor: 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
> > + * @index: CRTC which can be attached to the planes. The caller must ensure that
> > + *	   @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.
> 
> Should read:
> 
>  * @index: CRTC which can be attached to the plane. The caller must ensure that
>  *	   @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_formats.c b/drivers/gpu/drm/vkms/vkms_formats.c
> > index 040b7f113a3b..e8a5cc235ebb 100644
> > --- a/drivers/gpu/drm/vkms/vkms_formats.c
> > +++ b/drivers/gpu/drm/vkms/vkms_formats.c
> > @@ -9,24 +9,40 @@
> >  
> >  #include "vkms_formats.h"
> >  
> > +/**
> > + * pixel_offset() - Get the offset of the pixel at coordinates x/y in the first plane
> > + *
> > + * @frame_info: Buffer metadata
> > + * @x: The x coordinate of the wanted pixel in the buffer
> > + * @y: The y coordinate of the wanted pixel in the buffer
> > + *
> > + * The caller must ensure that the framebuffer associated with this request uses a pixel format
> > + * where block_h == block_w == 1.
> > + * If this requirement is not fulfilled, the resulting offset can point to an other pixel or
> > + * outside of the buffer.
> > + */
> >  static size_t pixel_offset(const struct vkms_frame_info *frame_info, int x, int y)
> >  {
> >  	return frame_info->offset + (y * frame_info->pitch)
> >  				  + (x * frame_info->cpp);
> >  }
> >  
> > -/*
> > - * packed_pixels_addr - Get the pointer to pixel of a given pair of coordinates
> > +/**
> > + * packed_pixels_addr() - Get the pointer to the block containing the pixel at the given
> > + * coordinates
> >   *
> >   * @frame_info: Buffer metadata
> > - * @x: The x(width) coordinate of the 2D buffer
> > - * @y: The y(Heigth) coordinate of the 2D buffer
> > + * @x: The x (width) coordinate inside the plane
> > + * @y: The y (height) coordinate inside the plane
> >   *
> >   * Takes the information stored in the frame_info, a pair of coordinates, and
> >   * returns the address of the first color channel.
> >   * This function assumes the channels are packed together, i.e. a color channel
> >   * comes immediately after another in the memory. And therefore, this function
> >   * doesn't work for YUV with chroma subsampling (e.g. YUV420 and NV21).
> > + *
> > + * The caller must ensure that the framebuffer associated with this request uses a pixel format
> > + * where block_h == block_w == 1, otherwise the returned pointer can be outside the buffer.
> >   */
> >  static void *packed_pixels_addr(const struct vkms_frame_info *frame_info,
> >  				int x, int y)
> > @@ -51,6 +67,13 @@ static int get_x_position(const struct vkms_frame_info *frame_info, int limit, i
> >  	return x;
> >  }
> >  
> > +/*
> > + * The following functions take pixel data from the buffer and convert them to the format
> > + * ARGB16161616 in @out_pixel.
> > + *
> > + * They are used in the vkms_compose_row() function to handle multiple formats.
> > + */
> > +
> >  static void ARGB8888_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
> >  {
> >  	/*
> > @@ -143,12 +166,11 @@ void vkms_compose_row(struct line_buffer *stage_buffer, struct vkms_plane_state
> >  }
> >  
> >  /*
> > - * The following  functions take an line of argb_u16 pixels from the
> > - * src_buffer, convert them to a specific format, and store them in the
> > - * destination.
> > + * The following functions take one &struct pixel_argb_u16 and convert it to a specific format.
> > + * The result is stored in @dst_pixels.
> >   *
> > - * They are used in the `compose_active_planes` to convert and store a line
> > - * from the src_buffer to the writeback buffer.
> > + * They are used in vkms_writeback_row() to convert and store a pixel from the src_buffer to
> > + * the writeback buffer.
> >   */
> >  static void argb_u16_to_ARGB8888(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
> >  {
> > @@ -214,6 +236,14 @@ static void argb_u16_to_RGB565(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
> >  	*pixels = cpu_to_le16(r << 11 | g << 5 | b);
> >  }
> >  
> > +/**
> > + * vkms_writeback_row() - Generic loop for all supported writeback format. It is executed just
> > + * after the blending to write a line in the writeback buffer.
> > + *
> > + * @wb: Job where to insert the final image
> > + * @src_buffer: Line to write
> > + * @y: Row to write in the writeback buffer
> > + */
> >  void vkms_writeback_row(struct vkms_writeback_job *wb,
> >  			const struct line_buffer *src_buffer, int y)
> >  {
> > @@ -227,6 +257,13 @@ void vkms_writeback_row(struct vkms_writeback_job *wb,
> >  		wb->pixel_write(dst_pixels, &in_pixels[x]);
> >  }
> >  
> > +/**
> > + * get_pixel_conversion_function() - Retrieve the correct read_pixel function for a specific
> > + * format. The returned pointer is NULL for unsupported pixel formats. The caller must ensure that
> > + * the pointer is valid before using it in a vkms_plane_state.
> > + *
> > + * @format: DRM_FORMAT_* value for which to obtain a conversion function (see [drm_fourcc.h])
> > + */
> >  void *get_pixel_conversion_function(u32 format)
> >  {
> >  	switch (format) {
> > @@ -245,6 +282,13 @@ void *get_pixel_conversion_function(u32 format)
> >  	}
> >  }
> >  
> > +/**
> > + * get_pixel_write_function() - Retrieve the correct write_pixel function for a specific format.
> > + * The returned pointer is NULL for unsupported pixel formats. The caller must ensure that the
> > + * pointer is valid before using it in a vkms_writeback_job.
> > + *
> > + * @format: DRM_FORMAT_* value for which to obtain a conversion function (see [drm_fourcc.h])
> > + */
> >  void *get_pixel_write_function(u32 format)
> >  {
> >  	switch (format) {
> > diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
> > index 5ce70dd946aa..56801e914208 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 */
> 
> It'd be great to clarify that BIT(0) == 1. Maybe?
> 
>   /* [1]: Allocation of a CRTC, its index will be BIT(0) = 1 */

Good catch, thanks!

> >  	ret = vkms_crtc_init(dev, crtc, &primary->base, &cursor->base);
> >  	if (ret)
> >  		return ret;
> > @@ -95,7 +103,11 @@ int vkms_output_init(struct vkms_device *vkmsdev, int index)
> >  		DRM_ERROR("Failed to init encoder\n");
> >  		goto err_encoder;
> >  	}
> > -	encoder->possible_crtcs = 1;
> > +	/*
> > +	 * This is a hardcoded value to select crtc for the encoder.
> > +	 * 1 here designate the first registered CRTC, the one allocated in [1]
> 
> BIT(0) here designate the first...
> 
> > +	 */
> > +	encoder->possible_crtcs = BIT(0);
> >  
> >  	ret = drm_connector_attach_encoder(connector, encoder);
> >  	if (ret) {

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