From: Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@...>
Sent: Friday, April 30, 2021 2:05 PM
To: devel@edk2.groups.io; Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@...>; Andrei Warkentin (awarkentin@...) <awarkentin@...>; Jeremy Linton <Jeremy.Linton@...>
Cc: Ard Biesheuvel <Ard.Biesheuvel@...>; leif@...; pete@...; Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@...>
Subject: RE: [edk2-devel] [PATCH 3/3] Platform/RaspberryPi/AcpiTables: Correct _DMA consumer

 

Update: UEFI Forum ASWG (ACPI spec working group) approved the submitted ECR as an errata for future ACPI 6.4 spec publication.

 

We can go ahead and proceed with this patch as submitted, based on that ECR clarification.

 

With that,

 

Reviewed-By: Samer El-Haj-Mahmoud Samer.El-Haj-Mahmoud@...

 

Thanks,

--Samer

 

 

 

Any further comments on the ACPI ECR documented in: https://bugzilla.tianocore.org/show_bug.cgi?id=3335 ?

 

I already have comments from Jeremey and Andrew saying it looks good. If there are no objections, I will let ASWG know to approve the ECR for future ACPI spec publication.

 

Thanks,

--Samer

 

 

 

 

 

I just got to this thread. Apologies for the delay.

 

I went through the ACPI spec. Here is what I see:

 

https://uefi.org/specs/ACPI/6.4/19_ASL_Reference/ACPI_Source_Language_Reference.html#qwordmemory-qword-memory-resource-descriptor-macro

 

“ResourceUsage specifies whether the Memory range is consumed by this device (ResourceConsumer) or passed on to child devices (ResourceProducer). If nothing is specified, then ResourceConsumer is assumed.”

https://uefi.org/specs/ACPI/6.4/06_Device_Configuration/Device_Configuration.html#dma-direct-memory-access

“ It specifies the ranges the bus controller (bridge) decodes on the child-side of its interface. (This is analogous to the _CRS object, which describes the resources that the bus controller decodes on the parent-side of its interface.) Any ranges described in the resources of a _DMA object can be used by child devices for DMA or bus master transactions..”

The way I read the spec, this wording in the _DMA definition “Any ranges described in the resources of a _DMA object can be used by child devices..” suggests that this should be a ResourceProducer, per the QWordMemory resource descriptor definition above

The _DMA example in section 6.2.4 uses a “ResourceConsumer”, when it should really be “ResourceProducer” according to these definitions: It describes , the child devices view of the address range, so the "translation" added is the CPU's view of the same range.

I submitted a “code first” ECR to correct the ACPI spec example (here : https://bugzilla.tianocore.org/show_bug.cgi?id=3335). Please provide feedback on the BZ (or this thread) whether you agree or not, so we can take this to ASWG/UEFI Forum for discussion and approval

Thanks,

--Samer

 

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