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iris: Explain how conditional aux accesses work

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Apart from an issue with fast clears that will be addressed soon,
aux-state tracking with conditional rendering works because the
aux-state info needed for performing required resolves is never lost.

Add comments explaining how this works. Assertions are omitted to avoid
having to pass render_condition variables into
iris_resource_prepare_access and iris_resource_finish_write.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7762>
This commit is contained in:
Nanley Chery 2021-01-08 10:18:28 -08:00 • committed by Marge Bot
parent 2d08711a2c
commit fc06683d07
1 changed files with 16 additions and 0 deletions
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16
src/gallium/drivers/iris/iris_resolve.c
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@ -709,6 +709,12 @@ iris_resource_prepare_access(struct iris_context *ice,
const enum isl_aux_op aux_op =
isl_aux_prepare_access(aux_state, aux_usage, fast_clear_supported);
/* Prepare the aux buffer for a conditional or unconditional access.
* A conditional access is handled by assuming that the access will
* not evaluate to a no-op. If the access does in fact occur, the aux
* will be in the required state. If it does not, no data is lost
* because the aux_op performed is lossless.
*/
if (aux_op == ISL_AUX_OP_NONE) {
/* Nothing to do here. */
} else if (isl_aux_usage_has_mcs(res->aux.usage)) {
@ -746,8 +752,18 @@ iris_resource_finish_write(struct iris_context *ice,
const uint32_t layer = start_layer + a;
const enum isl_aux_state aux_state =
iris_resource_get_aux_state(res, level, layer);
/* Transition the aux state for a conditional or unconditional write. A
* conditional write is handled by assuming that the write applies to
* only part of the render target. This prevents the new state from
* losing the types of compression that might exist in the current state
* (e.g. CLEAR). If the write evaluates to a no-op, the state will still
* be able to communicate when resolves are necessary (but it may
* falsely communicate this as well).
*/
const enum isl_aux_state new_aux_state =
isl_aux_state_transition_write(aux_state, aux_usage, false);
iris_resource_set_aux_state(ice, res, level, layer, 1, new_aux_state);
}
}