Message-ID: <Zzt2l0hZpKp4mniY@louis-chauvet-laptop>
Date: Mon, 18 Nov 2024 18:17:11 +0100
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: José Expósito <jose.exposito89@...il.com>
Cc: airlied@...il.com, arthurgrillo@...eup.net, corbet@....net,
	dri-devel@...ts.freedesktop.org, hamohammed.sa@...il.com,
	helen.koike@...labora.com, jeremie.dautheribes@...tlin.com,
	linux-doc@...r.kernel.org, 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, pekka.paalanen@...oniitty.fi,
	rdunlap@...radead.org, rodrigosiqueiramelo@...il.com,
	seanpaul@...gle.com, simona.vetter@...ll.ch, simona@...ll.ch,
	thomas.petazzoni@...tlin.com, tzimmermann@...e.de
Subject: Re: [PATCH v13 5/9] drm/vkms: Update pixels accessor to support
 packed and multi-plane formats.

On 18/11/24 - 18:10, José Expósito wrote:
> > Introduce the usage of block_h/block_w to compute the offset and the
> > pointer of a pixel. The previous implementation was specialized for
> > planes with block_h == block_w == 1. To avoid confusion and allow easier
> > implementation of tiled formats. It also remove the usage of the
> > deprecated format field `cpp`.
> > 
> > Introduce the plane_index parameter to get an offset/pointer on a
> > different plane.
> > 
> > Acked-by: Maíra Canal <mairacanal@...eup.net>
> > Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> > ---
> >  drivers/gpu/drm/vkms/vkms_formats.c | 114 ++++++++++++++++++++++++++++--------
> >  1 file changed, 91 insertions(+), 23 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/vkms/vkms_formats.c b/drivers/gpu/drm/vkms/vkms_formats.c
> > index 06aef5162529..7f932d42394d 100644
> > --- a/drivers/gpu/drm/vkms/vkms_formats.c
> > +++ b/drivers/gpu/drm/vkms/vkms_formats.c
> > @@ -10,22 +10,46 @@
> >  #include "vkms_formats.h"
> >  
> >  /**
> > - * pixel_offset() - Get the offset of the pixel at coordinates x/y in the first plane
> > + * packed_pixels_offset() - Get the offset of the block containing the pixel at coordinates x/y
> >   *
> >   * @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
> > + * @plane_index: The index of the plane to use
> > + * @offset: The returned offset inside the buffer of the block
> 
> The previous function (pixel_offset) returned a size_t for the offset rather
> than an int. Do you know if we are safe using an int in this case?

I think I used int everywhere because it may avoid strange issues with 
implicit casting and negative number. I don't remember exactly where, but 
Pekka suggested it.
 
> > + * @rem_x: The returned X coordinate of the requested pixel in the block
> > + * @rem_y: The returned Y coordinate of the requested pixel in the block
> >   *
> > - * 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.
> > + * As some pixel formats store multiple pixels in a block (DRM_FORMAT_R* for example), some
> > + * pixels are not individually addressable. This function return 3 values: the offset of the
> > + * whole block, and the coordinate of the requested pixel inside this block.
> > + * For example, if the format is DRM_FORMAT_R1 and the requested coordinate is 13,5, the offset
> > + * will point to the byte 5*pitches + 13/8 (second byte of the 5th line), and the rem_x/rem_y
> > + * coordinates will be (13 % 8, 5 % 1) = (5, 0)
> > + *
> > + * With this function, the caller just have to extract the correct pixel from the block.
> >   */
> > -static size_t pixel_offset(const struct vkms_frame_info *frame_info, int x, int y)
> > +static void packed_pixels_offset(const struct vkms_frame_info *frame_info, int x, int y,
> > +				 int plane_index, int *offset, int *rem_x, int *rem_y)
> >  {
> >  	struct drm_framebuffer *fb = frame_info->fb;
> > +	const struct drm_format_info *format = frame_info->fb->format;
> > +	/* Directly using x and y to multiply pitches and format->ccp is not sufficient because
> > +	 * in some formats a block can represent multiple pixels.
> > +	 *
> > +	 * Dividing x and y by the block size allows to extract the correct offset of the block
> > +	 * containing the pixel.
> > +	 */
> >  
> > -	return fb->offsets[0] + (y * fb->pitches[0]) + (x * fb->format->cpp[0]);
> > +	int block_x = x / drm_format_info_block_width(format, plane_index);
> > +	int block_y = y / drm_format_info_block_height(format, plane_index);
> > +	int block_pitch = fb->pitches[plane_index] * drm_format_info_block_height(format,
> > +										  plane_index);
> > +	*rem_x = x % drm_format_info_block_width(format, plane_index);
> > +	*rem_y = y % drm_format_info_block_height(format, plane_index);
> > +	*offset = fb->offsets[plane_index] +
> > +		  block_y * block_pitch +
> > +		  block_x * format->char_per_block[plane_index];
> >  }
> >  
> >  /**
> > @@ -35,30 +59,71 @@ static size_t pixel_offset(const struct vkms_frame_info *frame_info, int x, int
> >   * @frame_info: Buffer metadata
> >   * @x: The x (width) coordinate inside the plane
> >   * @y: The y (height) coordinate inside the plane
> > + * @plane_index: The index of the plane
> > + * @addr: The returned pointer
> > + * @rem_x: The returned X coordinate of the requested pixel in the block
> > + * @rem_y: The returned Y coordinate of the requested pixel in the block
> >   *
> > - * 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).
> > + * Takes the information stored in the frame_info, a pair of coordinates, and returns the address
> > + * of the block containing this pixel and the pixel position inside this block.
> >   *
> > - * 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.
> > + * See @packed_pixel_offset for details about rem_x/rem_y behavior.
> 
> Missing "s" in the name of the function. Should read "@packed_pixels_offset".

Thanks!

> >   */
> > -static void *packed_pixels_addr(const struct vkms_frame_info *frame_info,
> > -				int x, int y)
> > +static void packed_pixels_addr(const struct vkms_frame_info *frame_info,
> > +			       int x, int y, int plane_index, u8 **addr, int *rem_x,
> > +			       int *rem_y)
> >  {
> > -	size_t offset = pixel_offset(frame_info, x, y);
> > +	int offset;
> >  
> > -	return (u8 *)frame_info->map[0].vaddr + offset;
> > +	packed_pixels_offset(frame_info, x, y, plane_index, &offset, rem_x, rem_y);
> > +	*addr = (u8 *)frame_info->map[0].vaddr + offset;
> >  }
> >  
> > -static void *get_packed_src_addr(const struct vkms_frame_info *frame_info, int y)
> > +/**
> > + * packed_pixels_addr_1x1() - Get the pointer to the block containing the pixel at the given
> > + * coordinates
> > + *
> > + * @frame_info: Buffer metadata
> > + * @x: The x (width) coordinate inside the plane
> > + * @y: The y (height) coordinate inside the plane
> > + * @plane_index: The index of the plane
> > + * @addr: The returned pointer
> > + *
> > + * This function can only be used with format where block_h == block_w == 1.
> > + */
> > +static void packed_pixels_addr_1x1(const struct vkms_frame_info *frame_info,
> > +				   int x, int y, int plane_index, u8 **addr)
> > +{
> > +	int offset, rem_x, rem_y;
> 
> Nitpick, but it'd be nice if packed_pixels_offset() could take NULLs in
> the output values so we avoid declaring unused variables here and when
> calling packed_pixels_addr().

It is not a trivial change, and as I want this series to be merged I will 
send the v14 without it. But if I have the time I will send a new 
patch/series with this cleanup, thanks for the suggestion.

> > +
> > +	WARN_ONCE(drm_format_info_block_width(frame_info->fb->format,
> > +					      plane_index) != 1,
> > +		"%s() only support formats with block_w == 1", __func__);
> > +	WARN_ONCE(drm_format_info_block_height(frame_info->fb->format,
> > +					       plane_index) != 1,
> > +		"%s() only support formats with block_h == 1", __func__);
> > +
> > +	packed_pixels_offset(frame_info, x, y, plane_index, &offset, &rem_x,
> > +			     &rem_y);
> > +	*addr = (u8 *)frame_info->map[0].vaddr + offset;
> > +}
> > +
> > +static void *get_packed_src_addr(const struct vkms_frame_info *frame_info, int y,
> > +				 int plane_index)
> >  {
> >  	int x_src = frame_info->src.x1 >> 16;
> >  	int y_src = y - frame_info->rotated.y1 + (frame_info->src.y1 >> 16);
> > +	u8 *addr;
> > +	int rem_x, rem_y;
> > +
> > +	WARN_ONCE(drm_format_info_block_width(frame_info->fb->format, plane_index) != 1,
> > +		  "%s() only support formats with block_w == 1", __func__);
> > +	WARN_ONCE(drm_format_info_block_height(frame_info->fb->format, plane_index) != 1,
> > +		  "%s() only support formats with block_h == 1", __func__);
> >  
> > -	return packed_pixels_addr(frame_info, x_src, y_src);
> > +	packed_pixels_addr(frame_info, x_src, y_src, plane_index, &addr, &rem_x, &rem_y);
> > +
> > +	return addr;
> >  }
> >  
> >  static int get_x_position(const struct vkms_frame_info *frame_info, int limit, int x)
> > @@ -152,14 +217,14 @@ void vkms_compose_row(struct line_buffer *stage_buffer, struct vkms_plane_state
> >  {
> >  	struct pixel_argb_u16 *out_pixels = stage_buffer->pixels;
> >  	struct vkms_frame_info *frame_info = plane->frame_info;
> > -	u8 *src_pixels = get_packed_src_addr(frame_info, y);
> > +	u8 *src_pixels = get_packed_src_addr(frame_info, y, 0);
> >  	int limit = min_t(size_t, drm_rect_width(&frame_info->dst), stage_buffer->n_pixels);
> >  
> >  	for (size_t x = 0; x < limit; x++, src_pixels += frame_info->fb->format->cpp[0]) {
> >  		int x_pos = get_x_position(frame_info, limit, x);
> >  
> >  		if (drm_rotation_90_or_270(frame_info->rotation))
> > -			src_pixels = get_packed_src_addr(frame_info, x + frame_info->rotated.y1)
> > +			src_pixels = get_packed_src_addr(frame_info, x + frame_info->rotated.y1, 0)
> >  				+ frame_info->fb->format->cpp[0] * y;
> >  
> >  		plane->pixel_read(src_pixels, &out_pixels[x_pos]);
> > @@ -250,7 +315,10 @@ void vkms_writeback_row(struct vkms_writeback_job *wb,
> >  {
> >  	struct vkms_frame_info *frame_info = &wb->wb_frame_info;
> >  	int x_dst = frame_info->dst.x1;
> > -	u8 *dst_pixels = packed_pixels_addr(frame_info, x_dst, y);
> > +	u8 *dst_pixels;
> > +	int rem_x, rem_y;
> > +
> > +	packed_pixels_addr(frame_info, x_dst, y, 0, &dst_pixels, &rem_x, &rem_y);
> >  	struct pixel_argb_u16 *in_pixels = src_buffer->pixels;
> >  	int x_limit = min_t(size_t, drm_rect_width(&frame_info->dst), src_buffer->n_pixels);
> >  
> > 

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