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From: Melissa Wen <melissa.srw@gmail.com>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>,
	Sumera Priyadarsini <sylphrenadin@gmail.com>,
	Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>,
	David Airlie <airlied@linux.ie>,
	dri-devel@lists.freedesktop.org
Subject: Re: [PATCH v4 3/4] drm/vkms: add XRGB planes composition
Date: Mon, 26 Apr 2021 14:31:28 -0300	[thread overview]
Message-ID: <20210426173128.ybryk3taqf6usppv@smtp.gmail.com> (raw)
In-Reply-To: <YIbqF5IqofybM4k8@phenom.ffwll.local>

On 04/26, Daniel Vetter wrote:
> On Mon, Apr 26, 2021 at 11:03:15AM +0300, Pekka Paalanen wrote:
> > On Sat, 24 Apr 2021 05:25:31 -0300
> > Melissa Wen <melissa.srw@gmail.com> wrote:
> > 
> > > Add support for composing XRGB888 planes in addition to the ARGB8888
> > > format. In the case of an XRGB plane at the top, the composition consists
> > > of copying the RGB values of a pixel from src to dst and clearing alpha
> > > channel, without the need for alpha blending operations for each pixel.
> > > 
> > > Blend equations assume a completely opaque background, i.e., primary plane
> > > is not cleared before pixel blending but alpha channel is explicitly
> > > opaque (a = 0xff). Also, there is room for performance evaluation in
> > > switching pixel blend operation according to the plane format.
> > > 
> > > v4:
> > > - clear alpha channel (0xff) after blend color values by pixel
> > > - improve comments on blend ops to reflect the current state
> > > - describe in the commit message future improvements for plane composition
> > > 
> > > Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
> > > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > ---
> > >  drivers/gpu/drm/vkms/vkms_composer.c | 56 ++++++++++++++++++++++------
> > >  drivers/gpu/drm/vkms/vkms_plane.c    |  7 ++--
> > >  2 files changed, 48 insertions(+), 15 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> > > index 02642801735d..7e01bc39d2a1 100644
> > > --- a/drivers/gpu/drm/vkms/vkms_composer.c
> > > +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> > > @@ -4,6 +4,7 @@
> > >  
> > >  #include <drm/drm_atomic.h>
> > >  #include <drm/drm_atomic_helper.h>
> > > +#include <drm/drm_fourcc.h>
> > >  #include <drm/drm_gem_framebuffer_helper.h>
> > >  #include <drm/drm_gem_shmem_helper.h>
> > >  #include <drm/drm_vblank.h>
> > > @@ -64,7 +65,17 @@ static u8 blend_channel(u8 src, u8 dst, u8 alpha)
> > >  	return new_color;
> > >  }
> > >  
> > > -static void alpha_blending(const u8 *argb_src, u8 *argb_dst)
> > > +/**
> > > + * alpha_blend - alpha blending equation
> > > + * @argb_src: src pixel on premultiplied alpha mode
> > > + * @argb_dst: dst pixel completely opaque
> > > + *
> > > + * blend pixels using premultiplied blend formula. The current DRM assumption
> > > + * is that pixel color values have been already pre-multiplied with the alpha
> > > + * channel values. See more drm_plane_create_blend_mode_property(). Also, this
> > > + * formula assumes a completely opaque background.
> > > + */
> > > +static void alpha_blend(const u8 *argb_src, u8 *argb_dst)
> > >  {
> > >  	u8 alpha;
> > >  
> > > @@ -72,8 +83,16 @@ static void alpha_blending(const u8 *argb_src, u8 *argb_dst)
> > >  	argb_dst[0] = blend_channel(argb_src[0], argb_dst[0], alpha);
> > >  	argb_dst[1] = blend_channel(argb_src[1], argb_dst[1], alpha);
> > >  	argb_dst[2] = blend_channel(argb_src[2], argb_dst[2], alpha);
> > > -	/* Opaque primary */
> > > -	argb_dst[3] = 0xFF;
> > > +}
> > > +
> > > +/**
> > > + * x_blend - blending equation that ignores the pixel alpha
> > > + *
> > > + * overwrites RGB color value from src pixel to dst pixel.
> > > + */
> > > +static void x_blend(const u8 *xrgb_src, u8 *xrgb_dst)
> > > +{
> > > +	memcpy(xrgb_dst, xrgb_src, sizeof(u8) * 3);
> > 
> > Hi,
> > 
> > this function very clearly assumes a very specific pixel format on both
> > source and destination. I think it would be good if the code comments
> > called out exactly which DRM_FORMAT_* they assume. This would be good
> > to do on almost every function that makes such assumptions. I believe that
> > would help code readability, and also point out explicitly which things
> > need to be fixed when you add support for even more pixel formats.
> > 
> > "xrgb" and "argb" are IMO too vague. You might be referring to
> > DRM_FORMAT_XRGB* and DRM_FORMAT_ARGB*, or maybe you are referring to any
> > pixel format that happens to have or not have an alpha channel in
> > addition to the three RGB channels in some order and width.
> > 
> > Being explicit that these refer to specific DRM_FORMAT_* should also
> > help understanding how things work on big-endian CPUs. My current
> > understanding is that this memcpy is correct also on big-endian, given
> > DRM_FORMAT_XRGB8888.

This endianess issue seems a little tricky to me. I remember we have
already discussed something similar when introducing alpha blend ops.  I
took little endian as default by a code comment on
include/drm/drm_fourcc.h: DRM formats are little endian. But also, I am
not sure if I got it well.

> > 
> > Hmm, or rather, is this particular function intended to be general in
> > the sense that the order of RGB channels does not matter as long as it's
> > the same in both source and destination? Which would mean I had a wrong
> > assumption from the start.
> 
> Atm all vkms supports is X/ARGB8888, and even there we throw around random
> limits. Add support for more pixel formats is definitely on the list, and
> then all the blend/compose stuff needs to be quite drastically
> rearchitected.

yes, currently, we only have on vkms these two formats listed as
supported (X/ARGB8888), so, I think it is ok, since we do not expected
anything other than these two.

> 
> I think until we're there documenting what's already documented in the
> todo list feels like overkill.
> -Daniel
> 
> > 
> > >  }
> > >  
> > >  /**
> > > @@ -82,16 +101,20 @@ static void alpha_blending(const u8 *argb_src, u8 *argb_dst)
> > >   * @vaddr_src: source address
> > >   * @dst_composer: destination framebuffer's metadata
> > >   * @src_composer: source framebuffer's metadata
> > > + * @pixel_blend: blending equation based on plane format
> > >   *
> > > - * Blend the vaddr_src value with the vaddr_dst value using the pre-multiplied
> > > - * alpha blending equation, since DRM currently assumes that the pixel color
> > > - * values have already been pre-multiplied with the alpha channel values. See
> > > - * more drm_plane_create_blend_mode_property(). This function uses buffer's
> > > - * metadata to locate the new composite values at vaddr_dst.
> > > + * Blend the vaddr_src value with the vaddr_dst value using a pixel blend
> > > + * equation according to the plane format and clearing alpha channel to an
> > > + * completely opaque background. This function uses buffer's metadata to locate
> > > + * the new composite values at vaddr_dst.
> > > + *
> > > + * TODO: completely clear the primary plane (a = 0xff) before starting to blend
> > > + * pixel color values
> > >   */
> > >  static void blend(void *vaddr_dst, void *vaddr_src,
> > >  		  struct vkms_composer *dst_composer,
> > > -		  struct vkms_composer *src_composer)
> > > +		  struct vkms_composer *src_composer,
> > > +		  void (*pixel_blend)(const u8 *, u8 *))
> > >  {
> > >  	int i, j, j_dst, i_dst;
> > >  	int offset_src, offset_dst;
> > > @@ -119,7 +142,9 @@ static void blend(void *vaddr_dst, void *vaddr_src,
> > >  
> > >  			pixel_src = (u8 *)(vaddr_src + offset_src);
> > >  			pixel_dst = (u8 *)(vaddr_dst + offset_dst);
> > > -			alpha_blending(pixel_src, pixel_dst);
> > > +			pixel_blend(pixel_src, pixel_dst);
> > > +			/* clearing alpha channel (0xff)*/
> > > +			memset(vaddr_dst + offset_dst + 3, 0xff, 1);
> > 
> > A one byte memset?
> > 
> > Wouldn't pixel_dst[3] = 0xff; be more clear?

yes, I will change it.

Thanks for these suggestions,

Melissa
> > 
> > 
> > Thanks,
> > pq
> > 
> > >  		}
> > >  		i_dst++;
> > >  	}
> > > @@ -131,6 +156,8 @@ static void compose_plane(struct vkms_composer *primary_composer,
> > >  {
> > >  	struct drm_gem_object *plane_obj;
> > >  	struct drm_gem_shmem_object *plane_shmem_obj;
> > > +	struct drm_framebuffer *fb = &plane_composer->fb;
> > > +	void (*pixel_blend)(const u8 *p_src, u8 *p_dst);
> > >  
> > >  	plane_obj = drm_gem_fb_get_obj(&plane_composer->fb, 0);
> > >  	plane_shmem_obj = to_drm_gem_shmem_obj(plane_obj);
> > > @@ -138,8 +165,13 @@ static void compose_plane(struct vkms_composer *primary_composer,
> > >  	if (WARN_ON(!plane_shmem_obj->vaddr))
> > >  		return;
> > >  
> > > -	blend(vaddr_out, plane_shmem_obj->vaddr,
> > > -	      primary_composer, plane_composer);
> > > +	if (fb->format->format == DRM_FORMAT_ARGB8888)
> > > +		pixel_blend = &alpha_blend;
> > > +	else
> > > +		pixel_blend = &x_blend;
> > > +
> > > +	blend(vaddr_out, plane_shmem_obj->vaddr, primary_composer,
> > > +	      plane_composer, pixel_blend);
> > >  }
> > >  
> > >  static int compose_active_planes(void **vaddr_out,
> > > diff --git a/drivers/gpu/drm/vkms/vkms_plane.c b/drivers/gpu/drm/vkms/vkms_plane.c
> > > index 135140f8e87a..da4251aff67f 100644
> > > --- a/drivers/gpu/drm/vkms/vkms_plane.c
> > > +++ b/drivers/gpu/drm/vkms/vkms_plane.c
> > > @@ -16,8 +16,9 @@ static const u32 vkms_formats[] = {
> > >  	DRM_FORMAT_XRGB8888,
> > >  };
> > >  
> > > -static const u32 vkms_cursor_formats[] = {
> > > +static const u32 vkms_plane_formats[] = {
> > >  	DRM_FORMAT_ARGB8888,
> > > +	DRM_FORMAT_XRGB8888
> > >  };
> > >  
> > >  static struct drm_plane_state *
> > > @@ -200,8 +201,8 @@ struct vkms_plane *vkms_plane_init(struct vkms_device *vkmsdev,
> > >  	int nformats;
> > >  
> > >  	if (type == DRM_PLANE_TYPE_CURSOR) {
> > > -		formats = vkms_cursor_formats;
> > > -		nformats = ARRAY_SIZE(vkms_cursor_formats);
> > > +		formats = vkms_plane_formats;
> > > +		nformats = ARRAY_SIZE(vkms_plane_formats);
> > >  		funcs = &vkms_primary_helper_funcs;
> > >  	} else {
> > >  		formats = vkms_formats;
> > 
> 
> 
> 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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  reply	other threads:[~2021-04-26 17:31 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-24  8:22 [PATCH v4 0/4] drm/vkms: add overlay plane support Melissa Wen
2021-04-24  8:23 ` [PATCH v4 1/4] drm/vkms: init plane using drmm_universal_plane_alloc Melissa Wen
2021-04-24  8:24 ` [PATCH v4 2/4] drm/vkms: rename cursor to plane on ops of planes composition Melissa Wen
2021-04-24  8:25 ` [PATCH v4 3/4] drm/vkms: add XRGB " Melissa Wen
2021-04-26  8:03   ` Pekka Paalanen
2021-04-26 16:28     ` Daniel Vetter
2021-04-26 17:31       ` Melissa Wen [this message]
2021-04-27  8:10         ` Pekka Paalanen
2021-04-27  8:31           ` Melissa Wen
2021-04-27  9:04           ` Daniel Vetter
2021-04-24  8:26 ` [PATCH v4 4/4] drm/vkms: add overlay support Melissa Wen
2021-04-26  8:07   ` Pekka Paalanen
2021-04-26 17:07     ` Melissa Wen

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