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core/opregion: Avoid needless loads for fields marked Preserve #146

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core/opregion: Avoid needless loads for fields marked Preserve #146

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12 changes: 11 additions & 1 deletion core/opregion.c
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Original file line number Diff line number Diff line change
Expand Up @@ -482,7 +482,17 @@ void lai_write_field_internal(uint8_t *source, lai_nsnode_t *field) {

uint64_t value;
if (write_flag == FIELD_PRESERVE) {
if (field->type == LAI_NAMESPACE_FIELD || field->type == LAI_NAMESPACE_BANKFIELD) {
if (access_size == access_bits) {
// Don't needlessly read from the field if we're going to replace all of the bits.
// This is more in line with ACPICA's behavior, and the additional reads could've
// potentially confused hardware.

// If we're accessing the whole word, we can't start anywhere else.
LAI_ENSURE(bit_offset == 0);

value = 0;
} else if (field->type == LAI_NAMESPACE_FIELD
|| field->type == LAI_NAMESPACE_BANKFIELD) {
value = lai_perform_read(field->fld_region_node, access_size, offset);
} else if (field->type == LAI_NAMESPACE_INDEXFIELD) {
value = lai_perform_indexfield_read(field, access_size, offset);
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