Re: [PATCH v3 3/8] DynamicTablesPkg: AcpiSsdtPcieLibArm: Fix _PRT description

["Ard Biesheuvel" <ardb@kernel.org>]

(+ Marc)

On Fri, 28 Jan 2022 at 16:41, <Pierre.Gondois@arm.com> wrote:
>
> From: Pierre Gondois <Pierre.Gondois@arm.com>
>
> In ACPI 6.4, s6.2.13, _PRT objects describing PCI legacy interrupts
> can be defined following 2 models.
> In the first model, a _SRS object must be described to modify the PCI
> interrupt. The _CRS and _PRS object allows to describe the PCI
> interrupt (level/edge triggered, active high/low).
> In the second model, the PCI interrupt cannot be described with a
> similar granularity. PCI interrupts are by default level triggered,
> active low.
>
> GicV2 SPI interrupts are level or edge triggered, active high. To
> correctly describe PCI interrupts, the first model is used, even though
> Arm Base Boot Requirements v1.0 requires to use the second mode.
>

There are two different issues here:

- using separate 'interrupt link' device objects with an Interrupt()
resource rather than a simple GSIV number
- whether _PRS and _SRS need to be implemented on those link objects.

The latter is simply not true - _PRS and _SRS are optional, and
pointless if there is only a single possible value, so there is really
no need to add them here.

As for the choice between the link object or the GSIV number: I don't
think INTx interrupts on ARM systems are actually level low, and the
GSIV option is widely used, also in platforms that exist in
edk2-platforms, without any reported issues.

I've cc'ed Marc, perhaps he can shed some light on this, but I'd
prefer to stick to the GSIV approach if we can, as it is much simpler.



> Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com>
> ---
>
> Notes:
>     v3:
>      - New patch. [Pierre]
>
>  .../AcpiSsdtPcieLibArm/SsdtPcieGenerator.c    | 47 +++++++++++++++++--
>  1 file changed, 44 insertions(+), 3 deletions(-)
>
> diff --git a/DynamicTablesPkg/Library/Acpi/Arm/AcpiSsdtPcieLibArm/SsdtPcieGenerator.c b/DynamicTablesPkg/Library/Acpi/Arm/AcpiSsdtPcieLibArm/SsdtPcieGenerator.c
> index 3e22587d4a25..6823a98795c8 100644
> --- a/DynamicTablesPkg/Library/Acpi/Arm/AcpiSsdtPcieLibArm/SsdtPcieGenerator.c
> +++ b/DynamicTablesPkg/Library/Acpi/Arm/AcpiSsdtPcieLibArm/SsdtPcieGenerator.c
> @@ -1,7 +1,7 @@
>  /** @file
>    SSDT Pcie Table Generator.
>
> -  Copyright (c) 2021, Arm Limited. All rights reserved.<BR>
> +  Copyright (c) 2021 - 2022, Arm Limited. All rights reserved.<BR>
>
>    SPDX-License-Identifier: BSD-2-Clause-Patent
>
> @@ -295,6 +295,10 @@ GeneratePciDeviceInfo (
>      Method (_CRS, 0) {
>        Return CRS0
>        })
> +    Method (_PRS, 0) {
> +      Return CRS0
> +      })
> +    Method (_SRS, 1) { }
>      Method (_DIS) { }
>    }
>
> @@ -302,9 +306,12 @@ GeneratePciDeviceInfo (
>    PCI Firmware Specification - Revision 3.3,
>    s3.5. "Device State at Firmware/Operating System Handoff"
>
> -  The _PRS and _SRS are not supported, cf Arm Base Boot Requirements v1.0:
> +  Warning: The Arm Base Boot Requirements v1.0 states the following:
>    "The _PRS (Possible Resource Settings) and _SRS (Set Resource Settings)
>    are not supported."
> +  However, the first model to describe PCI legacy interrupts is used (cf. ACPI
> +  6.4 s6.2.13) as PCI defaults (Level Triggered, Active Low) are not compatible
> +  with GICv2 (must be Active High).
>
>    @param [in]       Irq         Interrupt controller interrupt.
>    @param [in]       IrqFlags    Interrupt flags.
> @@ -416,7 +423,41 @@ GenerateLinkDevice (
>      return Status;
>    }
>
> -  // ASL:Method (_DIS, 1) {}
> +  // ASL:
> +  // Method (_PRS, 0) {
> +  //   Return (CRS0)
> +  // }
> +  Status = AmlCodeGenMethodRetNameString (
> +             "_PRS",
> +             "CRS0",
> +             0,
> +             FALSE,
> +             0,
> +             LinkNode,
> +             NULL
> +             );
> +  if (EFI_ERROR (Status)) {
> +    ASSERT (0);
> +    return Status;
> +  }
> +
> +  // ASL:Method (_SRS, 1) {}
> +  // Not possible to disable interrupts.
> +  Status = AmlCodeGenMethodRetNameString (
> +             "_SRS",
> +             NULL,
> +             1,
> +             FALSE,
> +             0,
> +             LinkNode,
> +             NULL
> +             );
> +  if (EFI_ERROR (Status)) {
> +    ASSERT (0);
> +    return Status;
> +  }
> +
> +  // ASL:Method (_DIS, 0) {}
>    // Not possible to disable interrupts.
>    Status = AmlCodeGenMethodRetNameString (
>               "_DIS",
> --
> 2.25.1
>