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Add a 'preserve_config' field in struct GPEXConfig and, if set, generate the _DSM function #5 for preserving PCI boot configurations. This will be used for SMMUv3 accel=on support in subsequent patch. When SMMUv3 acceleration (accel=on) is enabled, QEMU exposes IORT Reserved Memory Region (RMR) nodes to support MSI doorbell translations. As per the Arm IORT specification, using IORT RMRs mandates the presence of _DSM function #5 so that the OS retains the firmware-assigned PCI configuration. Hence, this patch adds conditional support for generating _DSM #5. According to the ACPI Specification, Revision 6.6, Section 9.1.1 - “_DSM (Device Specific Method)”, " If Function Index is zero, the return is a buffer containing one bit for each function index, starting with zero. Bit 0 indicates whether there is support for any functions other than function 0 for the specified UUID and Revision ID. If set to zero, no functions are supported (other than function zero) for the specified UUID and Revision ID. If set to one, at least one additional function is supported. For all other bits in the buffer, a bit is set to zero to indicate if that function index is not supported for the specific UUID and Revision ID. (For example, bit 1 set to 0 indicates that function index 1 is not supported for the specific UUID and Revision ID.) " Please refer PCI Firmware Specification, Revision 3.3, Section 4.6.5 — "_DSM for Preserving PCI Boot Configurations" for Function 5 of _DSM method. Also, while at it, move the byte_list declaration to the top of the function for clarity. At the moment, DSM generation is not yet enabled. The resulting AML when preserve_config=true is: Method (_DSM, 4, NotSerialized) { If ((Arg0 == ToUUID ("e5c937d0-3553-4d7a-9117-ea4d19c3434d"))) { If ((Arg2 == Zero)) { Return (Buffer (One) { 0x21 }) } If ((Arg2 == 0x05)) { Return (Zero) } } ... } Cc: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Eric Auger <eric.auger@redhat.com> Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com> Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org> Tested-by: Eric Auger <eric.auger@redhat.com> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Message-id: 20260126104342.253965-23-skolothumtho@nvidia.com [Shameer: Removed possible duplicate _DSM creations] Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com> Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Tested-by: Eric Auger <eric.auger@redhat.com> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>