Message-ID: <CAMj1kXHmu=ykgBMRiFqG4_ra3FJtHa=GASoMUJswdMFa9v4Xgw@mail.gmail.com>
Date: Thu, 21 Dec 2023 15:30:40 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: "Chiu, Chasel" <chasel.chiu@...el.com>
Cc: Simon Glass <sjg@...omium.org>, 
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, Mark Rutland <mark.rutland@....com>, 
	Rob Herring <robh@...nel.org>, "Tan, Lean Sheng" <sheng.tan@...ements.com>, 
	lkml <linux-kernel@...r.kernel.org>, Dhaval Sharma <dhaval@...osinc.com>, 
	"Brune, Maximilian" <maximilian.brune@...ements.com>, Yunhui Cui <cuiyunhui@...edance.com>, 
	"Dong, Guo" <guo.dong@...el.com>, Tom Rini <trini@...sulko.com>, 
	ron minnich <rminnich@...il.com>, "Guo, Gua" <gua.guo@...el.com>, 
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>, U-Boot Mailing List <u-boot@...ts.denx.de>
Subject: Re: [PATCH v7 2/2] schemas: Add some common reserved-memory usages

On Tue, 28 Nov 2023 at 21:31, Chiu, Chasel <chasel.chiu@...el.com> wrote:
>
>
>
>
> > -----Original Message-----
> > From: Ard Biesheuvel <ardb@...nel.org>
> > Sent: Tuesday, November 28, 2023 10:08 AM
> > To: Chiu, Chasel <chasel.chiu@...el.com>
> > Cc: Simon Glass <sjg@...omium.org>; devicetree@...r.kernel.org; Mark Rutland
> > <mark.rutland@....com>; Rob Herring <robh@...nel.org>; Tan, Lean Sheng
> > <sheng.tan@...ements.com>; lkml <linux-kernel@...r.kernel.org>; Dhaval
> > Sharma <dhaval@...osinc.com>; Brune, Maximilian
> > <maximilian.brune@...ements.com>; Yunhui Cui <cuiyunhui@...edance.com>;
> > Dong, Guo <guo.dong@...el.com>; Tom Rini <trini@...sulko.com>; ron minnich
> > <rminnich@...il.com>; Guo, Gua <gua.guo@...el.com>; linux-
> > acpi@...r.kernel.org; U-Boot Mailing List <u-boot@...ts.denx.de>
> > Subject: Re: [PATCH v7 2/2] schemas: Add some common reserved-memory
> > usages
> >
> > You are referring to a 2000 line patch so it is not 100% clear where to look tbh.
> >
> >
> > On Tue, 21 Nov 2023 at 19:37, Chiu, Chasel <chasel.chiu@...el.com> wrote:
> > >
> > >
> > > In PR, UefiPayloadPkg/Library/FdtParserLib/FdtParserLib.c, line 268 is for
> > related example code.
> > >
> >
> > That refers to a 'memory-allocation' node, right? How does that relate to the
> > 'reserved-memory' node?
> >
> > And crucially, how does this clarify in which way "runtime-code" and "runtime-
> > data" reservations are being used?
> >
> > Since the very beginning of this discussion, I have been asking repeatedly for
> > examples that describe the wider context in which these reservations are used.
> > The "runtime" into runtime-code and runtime-data means that these regions have
> > a special significance to the operating system, not just to the next bootloader
> > stage. So I want to understand exactly why it is necessary to describe these
> > regions in a way where the operating system might be expected to interpret this
> > information and act upon it.
> >
>
>
> I think runtime code and data today are mainly for supporting UEFI runtime services - some BIOS functions for OS to utilize, OS may follow below ACPI spec to treat them as reserved range:
> https://uefi.org/specs/ACPI/6.5/15_System_Address_Map_Interfaces.html#uefi-memory-types-and-mapping-to-acpi-address-range-types
>
> Like I mentioned earlier, that PR is still in early phase and has not reflected all the required changes yet, but the idea is to build gEfiMemoryTypeInformationGuid HOB from FDT reserved-memory nodes.
> UEFI generic Payload has DxeMain integrated, however Memory Types are platform-specific, for example, some platforms may need bigger runtime memory for their implementation, that's why we want such FDT reserved-memory node to tell DxeMain.
>

> The Payload flow will be like this:
>   Payload creates built-in default MemoryTypes table ->
>     FDT reserved-memory node to override if required (this also ensures the same memory map cross boots so ACPI S4 works) ->
>       Build gEfiMemoryTypeInformationGuid HOB by "platfom specific" MemoryTypes Table ->
>         DxeMain/GCD to consume this MemoryTypes table and setup memory service ->
>           Install memory types table to UEFI system table.Configuration table...
>
> Note: if Payload built-in default MemoryTypes table works fine for the platform, then FDT reserved-memory node does not need to provide such 'usage' compatible strings. (optional)
> This FDT node could allow flexibility/compatibility without rebuilding Payload binary.
>
> Not sure if I answered all your questions, please highlight which area you need more information.
>

The gEfiMemoryTypeInformationGuid HOB typically carries platform
defaults, and the actual memory type information is kept in a
non-volatile EFI variable, which gets updated when the memory usage
changes. Is this different for UefiPayloadPkg?

(For those among the cc'ees less versed in EFI/EDK2: when you get the
'config changed -rebooting' message from the boot firmware, it
typically means that this memory type table has changed, and a reboot
is necessary.)

So the platform init needs to read this variable, or get the
information in a different way. I assume it is the payload, not the
platform init that updates the variable when necessary. This means the
information flows from payload(n) to platform init(n+1), where n is a
monotonic index tracking consecutive boots of the system.

Can you explain how the DT fits into this? How are the runtime-code
and runtime-data memory reservation nodes under /reserved-memory used
to implement this information exchange between platform init and
payload? And how do the HOB and the EFI variable fit into this
picture?

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