Builds upon the existing NVIDIA 16Bx2 block linear
format modifiers by adding more "fields" to the
existing parameterized
DRM_FORMAT_MOD_NVIDIA_16BX2_BLOCK format modifier
macro that allow fully defining a unique-across-
all-NVIDIA-hardware bit layout using a minimal
set of fields and values. The new modifier macro
DRM_FORMAT_MOD_NVIDIA_BLOCK_LINEAR_2D is
effectively backwards compatible with the existing
macro, introducing a superset of the previously
definable format modifiers.
Backwards compatibility has two quirks. First,
the zero value for the "kind" field, which is
implied by the DRM_FORMAT_MOD_NVIDIA_16BX2_BLOCK
macro, must be special cased in drivers and
assumed to map to the pre-Turing generic kind of
0xfe, since a kind of "zero" is reserved for
linear buffer layouts on all GPUs.
Second, it is assumed backwards compatibility
is only needed when running on Tegra GPUs, and
specifically Tegra GPUs prior to Xavier. This
is based on two assertions:
-Tegra GPUs prior to Xavier used a slightly
different raw bit layout than desktop GPUs,
making it impossible to directly share block
linear buffers between the two.
-Support for the existing block linear modifiers
was incomplete, making them useful only for
exporting buffers created by nouveau and
importing them to Tegra DRM as framebuffers for
scan out. There was no support for adding
framebuffers using format modifiers in nouveau,
nor importing dma-buf/PRIME GEM objects into
nouveau userspace drivers with modifiers in Mesa.
Hence it is assumed the prior modifiers were not
intended for use on desktop GPUs, and as a
corrolary, were not intended to support sharing
block linear buffers across two different NVIDIA
GPUs.
Signed-off-by: James Jones <jajo...@nvidia.com>
---
include/uapi/drm/drm_fourcc.h | 108 +++++++++++++++++++++++++++++++---
1 file changed, 100 insertions(+), 8 deletions(-)
diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
index 3feeaa3f987a..cc9853d42a24 100644
--- a/include/uapi/drm/drm_fourcc.h
+++ b/include/uapi/drm/drm_fourcc.h
@@ -497,7 +497,99 @@ extern "C" {
#define DRM_FORMAT_MOD_NVIDIA_TEGRA_TILED fourcc_mod_code(NVIDIA, 1)
/*
- * 16Bx2 Block Linear layout, used by desktop GPUs, and Tegra K1 and later
+ * Generalized Block Linear layout, used by desktop GPUs starting with
NV50/G80,
+ * and Tegra GPUs starting with Tegra K1.
+ *
+ * Pixels are arranged in Groups of Bytes (GOBs). GOB size and layout varies
+ * based on the architecture generation. GOBs themselves are then arranged in
+ * 3D blocks, with the block dimensions (in terms of GOBs) always being a power
+ * of two, and hence expressible as their log2 equivalent (E.g., "2" represents
+ * a block depth or height of "4").
+ *
+ * Chapter 20 "Pixel Memory Formats" of the Tegra X1 TRM describes this format
+ * in full detail.
+ *
+ * Macro
+ * Bits Param Description
+ * ---- -----
-----------------------------------------------------------------
+ *
+ * 3:0 h log2(height) of each block, in GOBs. Placed here for
+ * compatibility with the existing
+ * DRM_FORMAT_MOD_NVIDIA_16BX2_BLOCK()-based modifiers.
+ *
+ * 4:4 - Must be 1, to indicate block-linear layout. Necessary for
+ * compatibility with the existing
+ * DRM_FORMAT_MOD_NVIDIA_16BX2_BLOCK()-based modifiers.
+ *
+ * 8:5 - Reserved (To support 3D-surfaces with variable log2(depth) block
+ * size). Must be zero.
+ *
+ * Note there is no log2(width) parameter. Some portions of the
+ * hardware support a block width of two gobs, but it is
impractical
+ * to use due to lack of support elsewhere, and has no known
+ * benefits.
+ *
+ * 11:9 - Reserved (To support 2D-array textures with variable array
stride
+ * in blocks, specified via log2(tile width in blocks)). Must be
+ * zero.
+ *
+ * 19:12 k Page Kind. This value directly maps to a field in the page
+ * tables of all GPUs >= NV50. It affects the exact layout of bits
+ * in memory and can be derived from the tuple
+ *
+ * (format, GPU model, compression type, samples per pixel)
+ *
+ * Where compression type is defined below. If GPU model were
+ * implied by the format modifier, format, or memory buffer, page
+ * kind would not need to be included in the modifier itself, but
+ * since the modifier should define the layout of the associated
+ * memory buffer independent from any device or other context, it
+ * must be included here.
+ *
+ * To grandfather in prior block linear format modifiers to this
+ * layout, the page kind "0", which corresponds to "pitch/linear"
+ * and hence is unusable with block-linear layouts, is remapped
+ * within drivers to the value 0xfe, which corresponds to the
+ * "generic" kind used for simple single-sample color formats on
+ * pre-Turing GPUs.
