Re: [PATCH v1 4/6] ArmVirtPkg: Save DT base address from X0 in PCD

[Laszlo Ersek <lersek@redhat.com>]

On 10/12/18 16:40, Sami Mujawar wrote:
> Some virtual machine managers provide the base address of the DT
> in memory in the X0 register. Save the DT Base address in the
> PcdDeviceTreeInitialBaseAddress so that the firmware can use the
> PCD to parse the DT and obtain the platform information subsequently.
> 
> This change also requires that the PcdDeviceTreeInitialBaseAddress
> be a Dynamic PCD.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
> ---
> The changes can be seen at https://github.com/samimujawar/edk2/commit/57ffa0da043fd73907b24a6833d2797ea3dae564
> 
> Notes:
>     v1:
>     - Enable loading of DT from base address passed in X0.            [SAMI]
> 
>  ArmVirtPkg/ArmVirtPkg.dec                   | 12 ++++++++----
>  ArmVirtPkg/PrePi/AArch64/ModuleEntryPoint.S |  9 +++++++--
>  2 files changed, 15 insertions(+), 6 deletions(-)

This patch seems to overlap with a feature that (I think) Ard, Drew and
Eric have discussed earlier, for QEMU (floating RAM base). I suggest
coordinating as early as possible.

Thanks
Laszlo

> diff --git a/ArmVirtPkg/ArmVirtPkg.dec b/ArmVirtPkg/ArmVirtPkg.dec
> index 8f656fd2739dd1460891029f53953c765396f8fb..9d4b782a43e505079263ded2347dff2304c2a75c 100644
> --- a/ArmVirtPkg/ArmVirtPkg.dec
> +++ b/ArmVirtPkg/ArmVirtPkg.dec
> @@ -42,15 +42,19 @@ [Guids.common]
>  [Protocols]
>    gFdtClientProtocolGuid = { 0xE11FACA0, 0x4710, 0x4C8E, { 0xA7, 0xA2, 0x01, 0xBA, 0xA2, 0x59, 0x1B, 0x4C } }
>  
> -[PcdsFixedAtBuild, PcdsPatchableInModule]
> +[PcdsFixedAtBuild.common, PcdsDynamic.common, PcdsPatchableInModule.common]
>    #
>    # This is the physical address where the device tree is expected to be stored
> -  # upon first entry into UEFI. This needs to be a FixedAtBuild PCD, so that we
> -  # can do a first pass over the device tree in the SEC phase to discover the
> -  # UART base address.
> +  # upon first entry into UEFI. In some cases this needs to be a FixedAtBuild
> +  # PCD, so that we can do a first pass over the device tree in the SEC phase
> +  # to discover the UART base address. In other cases where the base address
> +  # for the DT is passed in X0 (by an earlier firmware stage or by a virtual
> +  # machine manager), this needs to be a PcdsDynamic so that the value can be
> +  # updated.
>    #
>    gArmVirtTokenSpaceGuid.PcdDeviceTreeInitialBaseAddress|0x0|UINT64|0x00000001
>  
> +[PcdsFixedAtBuild]
>    #
>    # Padding in bytes to add to the device tree allocation, so that the DTB can
>    # be modified in place (default: 256 bytes)
> diff --git a/ArmVirtPkg/PrePi/AArch64/ModuleEntryPoint.S b/ArmVirtPkg/PrePi/AArch64/ModuleEntryPoint.S
> index 891cf1fcab400c0842035be6a2fb003bafd63040..b5f8c9dd3c6a2bd2c937ff3891b2f51be65094d4 100644
> --- a/ArmVirtPkg/PrePi/AArch64/ModuleEntryPoint.S
> +++ b/ArmVirtPkg/PrePi/AArch64/ModuleEntryPoint.S
> @@ -1,5 +1,5 @@
>  //
> -//  Copyright (c) 2011-2013, ARM Limited. All rights reserved.
> +//  Copyright (c) 2011-2018, ARM Limited. All rights reserved.
>  //  Copyright (c) 2015-2016, Linaro Limited. All rights reserved.
>  //
>  //  This program and the accompanying materials
> @@ -143,8 +143,13 @@ ASM_PFX(DiscoverDramFromDt):
>    //
>    cbnz  x0, 0f
>    ldr   x0, PcdGet64 (PcdDeviceTreeInitialBaseAddress)
> +  b     1f
>  
> -0:mov   x29, x30            // preserve LR
> +  // Store the device tree base address.
> +0:adr   x8, PcdGet64 (PcdDeviceTreeInitialBaseAddress)
> +  str   x0, [x8]
> +
> +1:mov   x29, x30            // preserve LR
>    mov   x28, x0             // preserve DTB pointer
>    mov   x27, x1             // preserve base of image pointer
>  
>