Re: [edk2-platforms][PATCH 1/1] Platform/RaspberryPi/RPi4: Add _DSM ACPI method for 32-bit MMIO xHCI access

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

On Wed, 1 Sept 2021 at 18:46, Pete Batard <pete@akeo.ie> wrote:
>
> With the upcoming release of Windows 11, Microsoft has introduced a new USB
> Device-Specific Method (_DSM) function to enforce 64-bit xHCI registers to
> be accessed through two sequential 32-bit requests. The new function (Query
> controller register access type - Function 6) is documented at:
> https://docs.microsoft.com/en-us/windows-hardware/drivers/bringup/usb-device-specific-method---dsm-
>
> Support for this feature is required on the raspberry Pi 4 where there is
> a bug/limitation in the xHCI stack that prevents full range 64-bit access
> from working correctly. It should be noted that an equivalent for this _DSM
> is not required on Linux, as 64-bit xHCI register access is already broken
> down into 2x32-bit by the drivers there.
>
> With this _DSM, and unlike what is the case for Windows 10, Windows 11 can
> now be installed on the Raspberry Pi 4 without having to alter any of the
> installation files, as we were able to validate using the latest Windows 11
> Build 22000 Insider image.
>

Very nice!

> Signed-off-by: Pete Batard <pete@akeo.ie>
> Tested-by: Pete Batard <pete@akeo.ie>

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

Pushed as 6e68849e5545..901d3c52ed23

> ---
>  Platform/RaspberryPi/AcpiTables/Xhci.asl | 21 ++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/Platform/RaspberryPi/AcpiTables/Xhci.asl b/Platform/RaspberryPi/AcpiTables/Xhci.asl
> index 9b37277956d9..00b0cd29c69c 100644
> --- a/Platform/RaspberryPi/AcpiTables/Xhci.asl
> +++ b/Platform/RaspberryPi/AcpiTables/Xhci.asl
> @@ -138,6 +138,27 @@ DefinitionBlock (__FILE__, "SSDT", 5, "RPIFDN", "RPI4XHCI", 2)
>              Debug = "xHCI enable"
>              Store (0x6, CMND)
>          }
> +
> +        /*
> +         * Microsoft's USB Device-Specific Methods. See:
> +         * https://docs.microsoft.com/en-us/windows-hardware/drivers/bringup/usb-device-specific-method---dsm-
> +         */
> +        Name (DSMU, ToUUID ("ce2ee385-00e6-48cb-9f05-2edb927c4899"))
> +
> +        Method (_DSM, 4, Serialized) {
> +            If (LEqual (Arg0, DSMU)) {              // USB capabilities UUID
> +                Switch (ToInteger (Arg2)) {
> +                Case (0) {                          // Function 0: List of supported functions
> +                    Return (Buffer () { 0x41 })     // 0x41 - Functions 0 and 6 supported
> +                }
> +                Case (6) {                          // Function 6: RegisterAccessType
> +                    Return (Buffer () { 0x01 })     // 0x01 - Must use 32bit register access
> +                }
> +                Default { }                         // Unsupported
> +                }
> +            }
> +            return (Buffer () { 0x00 })             // Return 0x00 for anything unsupported
> +        }
>        } // end XHC0
>      } //end SCB0
>    } //end scope sb
> --
> 2.30.2.windows.1
>