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For certain address spaces, like the PCC (Platform Communications Channel), all access size values in a GAS (Generic Address Structure) are valid. Therefore, while this might make sense for other address spaces (like system memory), we cannot keep the enum with a subset of valid values.
The PCCT (Platform Communications Channel Table) is a generic mechanism for OSPM to communicate with an entity in the platform (e.g. a platform controller, or a Baseboard Management Controller (BMC)). The table provides access to a new namespace, to which Generic Address Structures (GAS) in other tables can refer to. Each entry in the PCCT is an addressable subspace, which provides the address and length of a shared memory region that can be used for communication with the platform. Subspaces may also have a doorbell register to notify the platform of certain events, as well as additional registers.
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@IsaacWoods have you had time to review this? |
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Wow, thanks for working on this and apologies for the delay in reviewing. I have not had the chance to look into the PCC very much, but have just glanced over the section in the spec. Have you managed to test this with a machine that actually has the tables for the PCC - I can imagine it existing mainly on servers with BMCs but maybe it is present on e.g. enterprise thin-clients with BMCs for remote management? I'll hopefully have a chance to sit and look through the structures in detail soon, but they don't look unreasonable at first glance. One thing you could address is the master/slave terminology - I can see that they're the terms used by the spec, but I generally try to avoid them, and this is an instance where they don't even really seem to make sense. I'll leave an alternative up to you - something like Ospm and Firmware / Controller and Platform, whatever really. |
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The PCCT (Platform Communications Channel Table) is a generic mechanism for OSPM to communicate with an entity in the platform (e.g. a platform controller, or a Baseboard Management Controller (BMC)).
The table provides access to a new namespace, to which Generic Address Structures (GAS) in other tables can refer to. Each entry in the PCCT is an addressable subspace, which provides the address and length of a shared memory region that can be used for communication with the platform. Subspaces may also have a doorbell register to notify the platform of certain events, as well as additional registers.
See the ACPI spec for more information: https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/14_Platform_Communications_Channel/Platform_Comm_Channel.html
Unfortunately for us, the PCC address space allows all access size values (as opposed to e.g. system memory, which only allows 1, 2, 4 and 8-byte access sizes), which means we must remove the
AccessSizeenum, and have a regularu8in theGenericAddressstruct.