Message-ID: <ZgLwSwck8iixjmjB@localhost.localdomain>
Date: Tue, 26 Mar 2024 16:56:59 +0100
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Pekka Paalanen <pekka.paalanen@...labora.com>
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
	Melissa Wen <melissa.srw@...il.com>,
	Maíra Canal <mairacanal@...eup.net>,
	Haneen Mohammed <hamohammed.sa@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, arthurgrillo@...eup.net,
	Jonathan Corbet <corbet@....net>, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, jeremie.dautheribes@...tlin.com,
	miquel.raynal@...tlin.com, thomas.petazzoni@...tlin.com,
	seanpaul@...gle.com, marcheu@...gle.com, nicolejadeyee@...gle.com
Subject: Re: [PATCH v5 07/16] drm/vkms: Update pixels accessor to support
 packed and multi-plane formats.

Le 25/03/24 - 14:40, Pekka Paalanen a écrit :
> On Wed, 13 Mar 2024 18:45:01 +0100
> Louis Chauvet <louis.chauvet@...tlin.com> 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.
> > 
> > Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> > ---
> >  drivers/gpu/drm/vkms/vkms_formats.c | 76 +++++++++++++++++++++++++------------
> >  1 file changed, 52 insertions(+), 24 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/vkms/vkms_formats.c b/drivers/gpu/drm/vkms/vkms_formats.c
> > index b2f8dfc26c35..649d75d05b1f 100644
> > --- a/drivers/gpu/drm/vkms/vkms_formats.c
> > +++ b/drivers/gpu/drm/vkms/vkms_formats.c
> > @@ -10,23 +10,43 @@
> >  #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
> > + * @rem_x,@rem_y: The returned 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);
> > +	*rem_x = x % drm_format_info_block_width(format, plane_index);
> > +	*rem_y = x % drm_format_info_block_height(format, plane_index);
> 
> typo: x should be y

Fixed in v6.
 
> 
> > +	*offset = fb->offsets[plane_index] +
> > +		  block_y * fb->pitches[plane_index] +
> > +		  block_x * format->char_per_block[plane_index];
> >  }
> 
> Ok, this function looks very much plausible for handling blocky
> formats. Good.

Thanks!

> >  
> >  /**
> > @@ -36,30 +56,35 @@ 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,@rem_y: The returned 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.
> >   */
> > -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)
> > +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;
> >  
> > -	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);
> 
> How can the caller be not interested in rem_x, rem_y?

At this point of the series, I did not change how the rest was working. As 
this function will be deleted later, I just adapted it to use the new 
packed_pixel_addr implementation.
 
> Maybe there is no IGT test that uses DRM_FORMAT_R1 FB on a plane and
> has a source rectangle whose x is not divisible by 8 pixels?
> Or maybe the FB is filled with a solid color instead of a pattern that
> would show source rectangle positioning problems?

Currently, there is no DRM_FORMAT_R1 test in IGT, and all formats 
supported by VKMS are aligned on 8/16 bits with block_w == block_h == 1, 
so rem_x and rem_y will be equal to zero.

> Maybe at this point of the series, this should assert that rem_x and
> rem_y are zero? That's what vkms_compose_row() assumes, right?

Even more specificaly, vkms_compose_row() assumes that
block_w == block_h == 1, so maybe more

	WARN_ONCE(drm_format_info_block_width(format, plane_index) != 1, "get_packed_pixel_addr() only support formats with block_w == 1");
	WARN_ONCE(drm_format_info_block_hieght(format, plane_index) != 1, "get_packed_pixel_addr() only support formats with block_h == 1");

Thanks,
Louis Chauvet

> 
> Thanks,
> pq
> 
> > +	return addr;
> >  }
> >  
> >  static int get_x_position(const struct vkms_frame_info *frame_info, int limit, int x)
> > @@ -168,14 +193,14 @@ 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]);
> > @@ -276,7 +301,10 @@ 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);
> >  
> > 
> 



-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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