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| -rw-r--r-- | src/commonlib/include/commonlib/coreboot_tables.h | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/src/commonlib/include/commonlib/coreboot_tables.h b/src/commonlib/include/commonlib/coreboot_tables.h index eaa3c4eec0..f411ff206b 100644 --- a/src/commonlib/include/commonlib/coreboot_tables.h +++ b/src/commonlib/include/commonlib/coreboot_tables.h @@ -211,6 +211,45 @@ struct lb_forward { uint64_t forward; }; +/** + * coreboot framebuffer + * + * The coreboot framebuffer uses a very common format usually referred + * to as "linear framebuffer": + * + * The first pixel of the framebuffer is the upper left corner, its + * address is given by `physical_address`. + * + * Each pixel is represented by exactly `bits_per_pixel` bits. If a + * pixel (or a color component therein) doesn't fill a whole byte or + * doesn't start on a byte boundary, it starts at the least signifi- + * cant bit not occupied by the previous pixel (or color component). + * Pixels (or color components) that span multiple bytes always start + * in the byte with the lowest address. + * + * The framebuffer provides a visible rectangle of `x_resolution` * + * `y_resolution` pixels. However, the lines always start at a byte + * boundary given by `bytes_per_line`, which may leave a gap after + * each line of pixels. Thus, the data for a pixel with the coordi- + * nates (x, y) from the upper left corner always starts at + * + * physical_address + y * bytes_per_line + x * bits_per_pixel / 8 + * + * `bytes_per_line` is always big enough to hold `x_resolution` + * pixels. It can, however, be arbitrarily higher (e.g. to fulfill + * hardware constraints or for optimization purposes). The size of + * the framebuffer is always `y_resolution * bytes_per_line`. + * + * The coreboot framebuffer only supports RGB color formats. The + * position and size of each color component are specified indivi- + * dually by <color>_mask_pos and <color>_mask_size. To allow byte + * or word aligned pixels, a fourth (padding) component may be + * specified by `reserved_mask_pos` and `reserved_mask_size`. + * + * Software utilizing the coreboot framebuffer shall consider all + * fields described above. It may, however, only implement a subset + * of the possible color formats. + */ #define LB_TAG_FRAMEBUFFER 0x0012 struct lb_framebuffer { uint32_t tag; |