[Xen-devel] Xen: ARM: Support for mapping OperationRegion in ACPI ASL

[Jiandi An <anjiandi@xxxxxxxxxxxxxx>]

Hi Guys,

Xen currently does not handle mapping of MMIO regions specified under 
OperationRegion in ACPI ASL.  OperationRegion is well defined in ACPI 
specification.  I'm seeking for architectural direction on adding support for 
mapping OperationRegion.

Some context here.  Mapping of resources specificed under _CRS in ACPI is 
handled by dom0 requesting Xen to map as platform devices are added.  
https://lwn.net/Articles/674666/ provided service xen_map_device_mmio() in dom0 
to call Xen to map and it's done so by registering xen_platform_notifier() 
platform bus driver.  This covers the platform devices.

The OperationRegion access in dom0 is in acpica path.  The following is a stack 
of the code path where OperationRegion is parsed.  
acpi_ex_system_memory_space_handler() gets the parsed address specified in 
OperationRegion in ACPI and maps it then performs the memory read or write.  

acpi_ex_system_memory_space_handler+0x378/0x424
acpi_ev_address_space_dispatch+0x294/0x310
acpi_ex_access_region+0x3c0/0x468
acpi_ex_field_datum_io+0x14c/0x380
acpi_ex_extract_from_field+0xe8/0x2f4
acpi_ex_read_data_from_field+0x330/0x38c
acpi_ex_resolve_node_to_value+0x310/0x3fc
acpi_ex_resolve_to_value+0x354/0x3e8
acpi_ds_evaluate_name_path+0xa4/0x15c
acpi_ds_exec_end_op+0xbc/0x6c8
acpi_ps_parse_loop+0x7ac/0x840
acpi_ps_parse_aml+0x1c4/0x434
acpi_ps_execute_method+0x1f0/0x2a0
acpi_ns_evaluate+0x2e4/0x424
acpi_ut_evaluate_object+0xb0/0x250
acpi_ut_execute_STA+0xb0/0x164
acpi_ns_init_one_device+0xac/0x250
acpi_ns_walk_namespace+0x108/0x254
acpi_ns_initialize_devices+0x274/0x35c
acpi_initialize_objects+0x90/0xf0
acpi_init+0xc0/0x30c
do_one_initcall+0x44/0x138
kernel_init_freeable+0x148/0x1ec
kernel_init+0x18/0x108

The workaround in testing for handling OperationRegion I did is to call 
xen_map_device_mmio() to map the resource specificied in OperationRegion if 
it's dom0 running under XEN in acpi_ex_system_memory_space_handler().  But this 
is a fairly generic ACPI code path.  Looking for achitectural suggestion to 
properly handle OperationRegion for Xen on ARM.

Thanks.

-- 
Jiandi An
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm 
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux 
Foundation Collaborative Project.

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