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[acpi] Generalise DSDT/SSDT data extraction logic

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Allow for the DSDT/SSDT signature-scanning and value extraction code
to be reused for extracting a pass-through MAC address.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2021-09-08 12:53:12 +01:00
parent e09e1142a3
commit 02ec659b73
3 changed files with 98 additions and 68 deletions
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70
src/arch/x86/interface/pcbios/acpipwr.c
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@@ -42,6 +42,69 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
/** _S5_ signature */
#define S5_SIGNATURE ACPI_SIGNATURE ( '_', 'S', '5', '_' )
/**
* Extract \_Sx value from DSDT/SSDT
*
* @v zsdt DSDT or SSDT
* @v len Length of DSDT/SSDT
* @v offset Offset of signature within DSDT/SSDT
* @v data Data buffer
* @ret rc Return status code
*
* In theory, extracting the \_Sx value from the DSDT/SSDT requires a
* full ACPI parser plus some heuristics to work around the various
* broken encodings encountered in real ACPI implementations.
*
* In practice, we can get the same result by scanning through the
* DSDT/SSDT for the signature (e.g. "_S5_"), extracting the first
* four bytes, removing any bytes with bit 3 set, and treating
* whatever is left as a little-endian value. This is one of the
* uglier hacks I have ever implemented, but it's still prettier than
* the ACPI specification itself.
*/
static int acpi_extract_sx ( userptr_t zsdt, size_t len, size_t offset,
void *data ) {
unsigned int *sx = data;
uint8_t bytes[4];
uint8_t *byte;
/* Skip signature and package header */
offset += ( 4 /* signature */ + 3 /* package header */ );
/* Sanity check */
if ( ( offset + sizeof ( bytes ) /* value */ ) > len ) {
return -EINVAL;
}
/* Read first four bytes of value */
copy_from_user ( bytes, zsdt, offset, sizeof ( bytes ) );
DBGC ( colour, "ACPI found \\_Sx containing %02x:%02x:%02x:%02x\n",
bytes[0], bytes[1], bytes[2], bytes[3] );
/* Extract \Sx value. There are three potential encodings
* that we might encounter:
*
* - SLP_TYPa, SLP_TYPb, rsvd, rsvd
*
* - <byteprefix>, SLP_TYPa, <byteprefix>, SLP_TYPb, ...
*
* - <dwordprefix>, SLP_TYPa, SLP_TYPb, 0, 0
*
* Since <byteprefix> and <dwordprefix> both have bit 3 set,
* and valid SLP_TYPx must have bit 3 clear (since SLP_TYPx is
* a 3-bit field), we can just skip any bytes with bit 3 set.
*/
byte = bytes;
if ( *byte & 0x08 )
byte++;
*sx = *(byte++);
if ( *byte & 0x08 )
byte++;
*sx |= ( *byte << 8 );
return 0;
}
/**
* Power off the computer using ACPI
*
@@ -56,7 +119,7 @@ int acpi_poweroff ( void ) {
unsigned int pm1b_cnt;
unsigned int slp_typa;
unsigned int slp_typb;
int s5;
unsigned int s5;
int rc;
/* Locate FADT */
@@ -74,9 +137,8 @@ int acpi_poweroff ( void ) {
pm1b_cnt = ( pm1b_cnt_blk + ACPI_PM1_CNT );
/* Extract \_S5 from DSDT or any SSDT */
s5 = acpi_sx ( S5_SIGNATURE );
if ( s5 < 0 ) {
rc = s5;
if ( ( rc = acpi_extract ( S5_SIGNATURE, &s5,
acpi_extract_sx ) ) != 0 ) {
DBGC ( colour, "ACPI could not extract \\_S5: %s\n",
strerror ( rc ) );
return rc;