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
corollary, were not intended to support sharing
block linear buffers across two different NVIDIA
GPUs.
v2:
- Added canonicalize helper function
v3:
- Added additional bit to compression field to
support Tesla (NV5x,G8x,G9x,GT1xx,GT2xx) class
chips.
Signed-off-by: James Jones <jajones@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
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