Hi Pekka,
On Thu, Feb 17, 2022 at 11:10 AM Pekka Paalanen <ppaalanen@xxxxxxxxx> wrote:
On Tue, 15 Feb 2022 17:52:26 +0100
Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
Introduce a fourcc code for a single-channel frame buffer format with two
darkness levels. This can be used for two-level dark-on-light displays.
As the number of bits per pixel is less than eight, this relies on
proper block handling for the calculation of bits per pixel and pitch.
Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
--- a/drivers/gpu/drm/drm_fourcc.c
+++ b/drivers/gpu/drm/drm_fourcc.c
@@ -151,6 +151,8 @@ const struct drm_format_info *__drm_format_info(u32 format)
{ .format = DRM_FORMAT_C4, .depth = 4, .num_planes = 1,
.char_per_block = { 1, }, .block_w = { 2, }, .block_h = { 1, }, .hsub = 1, .vsub = 1 },
{ .format = DRM_FORMAT_C8, .depth = 8, .num_planes = 1, .cpp = { 1, 0, 0 }, .hsub = 1, .vsub = 1 },
+ { .format = DRM_FORMAT_D1, .depth = 1, .num_planes = 1,
+ .char_per_block = { 1, }, .block_w = { 8, }, .block_h = { 1, }, .hsub = 1, .vsub = 1 },
{ .format = DRM_FORMAT_R1, .depth = 1, .num_planes = 1,
.char_per_block = { 1, }, .block_w = { 8, }, .block_h = { 1, }, .hsub = 1, .vsub = 1 },
{ .format = DRM_FORMAT_R2, .depth = 2, .num_planes = 1,
diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
index 8605a1acc6813e6c..c15c6efcc65e5827 100644
--- a/include/uapi/drm/drm_fourcc.h
+++ b/include/uapi/drm/drm_fourcc.h
@@ -104,6 +104,9 @@ extern "C" {
#define DRM_FORMAT_C4 fourcc_code('C', '4', ' ', ' ') /* [3:0] C */
#define DRM_FORMAT_C8 fourcc_code('C', '8', ' ', ' ') /* [7:0] C */
+/* 1 bpp Darkness */
+#define DRM_FORMAT_D1 fourcc_code('D', '1', ' ', ' ') /* [0] D */
+
the same comment here as for C1 and R1 formats, need to specify pixel
ordering inside a byte.
Right, will do.
I think it would also be good to explain the rationale why C1 and R1
are not suitable for this case and we need yet another 1-bit format in
the commit message.
For posterity, of course. I roughly remember the discussions.
C1 is color-indexed, which can be any two colors.
R1 is light-on-dark.
D1 is dark-on-light.
I also wonder if anyone would actually use D1. Should it be added
anyway? There is no rule that a pixel format must be used inside the
kernel AFAIK, but is there even a prospective userspace wanting this?
Exposing R1 and inverting bits while copying to hardware might be
enough?
That's an option. The repaper driver does that:
drm_fb_xrgb8888_to_gray8(buf, 0, cma_obj->vaddr, fb, &clip);
repaper_gray8_to_mono_reversed(buf, fb->width, fb->height);
Can drm_framebuffer objects be backed by graphics memory, i.e.
can they be displayed without copying?
/* 1 bpp Red */
#define DRM_FORMAT_R1 fourcc_code('R', '1', ' ', ' ') /* [0] R */
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
