[PATCH] acpi/gpex: Inform os to keep firmware resource map

[Jiahui Cen <cenjiahui@huawei.com>]

There may be some differences in pci resource assignment between guest os
and firmware.

Eg. A Bridge with Bus [d2]
    -+-[0000:d2]---01.0-[d3]----01.0

    where [d2:01.00] is a pcie-pci-bridge with BAR0 (mem, 64-bit, non-pref) [size=256]
          [d3:01.00] is a PCI Device with BAR0 (mem, 64-bit, pref) [size=128K]
                                          BAR4 (mem, 64-bit, pref) [size=64M]

    In EDK2, the Resource Map would be:
        PciBus: Resource Map for Bridge [D2|01|00]
        Type = PMem64; Base = 0x8004000000;     Length = 0x4100000;     Alignment = 0x3FFFFFF
           Base = 0x8004000000; Length = 0x4000000;     Alignment = 0x3FFFFFF;  Owner = PCI [D3|01|00:20]
           Base = 0x8008000000; Length = 0x20000;       Alignment = 0x1FFFF;    Owner = PCI [D3|01|00:10]
        Type =  Mem64; Base = 0x8008100000;     Length = 0x100; Alignment = 0xFFF

    While in Linux, kernel will use 0x2FFFFFF as the alignment to calculate
    the PMem64 size, which would be 0x6000000.

The diffences could result in resource assignment failure.

Using _DSM #5 method to inform guest os not to ignore the PCI configuration
that firmware has done at boot time could handle the differences.

Signed-off-by: Jiahui Cen <cenjiahui@huawei.com>
---
 hw/pci-host/gpex-acpi.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/hw/pci-host/gpex-acpi.c b/hw/pci-host/gpex-acpi.c
index 071aa11b5c..2b490f3379 100644
--- a/hw/pci-host/gpex-acpi.c
+++ b/hw/pci-host/gpex-acpi.c
@@ -112,10 +112,19 @@ static void acpi_dsdt_add_pci_osc(Aml *dev)
     UUID = aml_touuid("E5C937D0-3553-4D7A-9117-EA4D19C3434D");
     ifctx = aml_if(aml_equal(aml_arg(0), UUID));
     ifctx1 = aml_if(aml_equal(aml_arg(2), aml_int(0)));
-    uint8_t byte_list[1] = {1};
+    uint8_t byte_list[1] = {0x21};
     buf = aml_buffer(1, byte_list);
     aml_append(ifctx1, aml_return(buf));
     aml_append(ifctx, ifctx1);
+
+    /* PCI Firmware Specification 3.2
+     * 4.6.5. _DSM for Ignoring PCI Boot Configurations
+     * The UUID in _DSM in this context is
+     * {E5C937D0-3553-4D7A-9117-EA4D19C3434D}
+     */
+    ifctx1 = aml_if(aml_equal(aml_arg(2), aml_int(5)));
+    aml_append(ifctx1, aml_return(aml_int(0)));
+    aml_append(ifctx, ifctx1);
     aml_append(method, ifctx);
 
     byte_list[0] = 0;
-- 
2.28.0