On Tue, Apr 27, 2021 at 11:10:59AM +0300, Pekka Paalanen wrote: > On Mon, 26 Apr 2021 14:31:28 -0300 > Melissa Wen <melissa.srw@xxxxxxxxx> wrote: > > > 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@xxxxxxxxx> 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@xxxxxxxxx> > > > > > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > > > > > --- > > > > > 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. > > DRM format *definitions* are written on a little-endian CPU. When you > have a big-endian CPU, the byte-to-byte memory contents still remain > the same. That means if you have a uint32_t pixel in a certain > DRM_FORMAT_*, you must always access the bits of it like a > little-endian CPU would. > > I think this was the "recently" agreed definition, and drivers who do > not follow this still exist because fixing them would break userspace? Legacy AddFb might give you a big endia drm_fourcc on some drivers. AddFb2 will not play such tricks. Also big-endian is dead, imo if someone cares enough about it they could make "fix vkms for big-endian" a nice project :-) -Daniel > So if you make the assumption that your machine is little-endian, you > have no worries, but you might want to document that you are making > this assumption, so that people know it might not be correct on > big-endian. It is important to document that it is *unknown* if the > code is correct on big-endian, to make people think rather than blindly > add a #ifdef big-endian then swap bytes, because the code might be > correct already - you just don't know yet. > > I wouldn't personally bother thinking about big-endian, other than > acknowledging that I don't think about big-endian when writing code, and > noticing places where it might make a difference (prime example: > accessing pixel components via bytes vs. bits-of-uint32). > > > > > 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. > > If there are arbitrary limitations, then IMO those are especially > important to mention. > > > 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. > > I'm literally asking for single-sentence comments added, like: > > /* DRM_FORMAT_XRGB8888 */ > > It makes all the difference to anyone seeing the code for the first > time. Particularly if people want to review patches into this area, > because patches are sent via email and therefore completely lack the > context of the surrounding code at large and knowledge of which kernel > tree they apply to (I'm not a kernel dev), not to mention the trouble > of having to apply a patch to be able to look at more context. > > Thanks for mentioning https://lkml.org/lkml/2020/8/30/163 in the other > email! > > > Thanks, > pq > > > > > -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@xxxxxxxxxxxxxxxxxxxxx > > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > > > > > > -- > > > Daniel Vetter > > > Software Engineer, Intel Corporation > > > http://blog.ffwll.ch > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel