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Subject: Re: [PATCH v3 07/15] ArmVirtPkg: Early serial port initialisation
To: Sami Mujawar <sami.mujawar@arm.com>, devel@edk2.groups.io
Cc: leif@nuviainc.com, lersek@redhat.com, Alexandru.Elisei@arm.com,
 Andre.Przywara@arm.com, Matteo.Carlini@arm.com, Laura.Moretta@arm.com,
 nd@arm.com, Julien Grall <julien@xen.org>
References: <20200624133458.61920-1-sami.mujawar@arm.com>
 <20200624133458.61920-8-sami.mujawar@arm.com>
From: "Ard Biesheuvel" <ard.biesheuvel@arm.com>
Message-ID: <2b729fe3-83f3-52f0-9124-f908cbaf61cd@arm.com>
Date: Thu, 25 Jun 2020 13:42:01 +0200
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(+ Julien)

On 6/24/20 3:34 PM, Sami Mujawar wrote:
> Initialise serial port early so that the platform
> memory map can be logged.
> 
> Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
> ---
>   ArmVirtPkg/PrePi/PrePi.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/ArmVirtPkg/PrePi/PrePi.c b/ArmVirtPkg/PrePi/PrePi.c
> index 4f0c3f98bad63d0682cccd76a0a062d1fd4f46ab..5e144f4bdefb810708238097a3373f11d150bfe5 100755
> --- a/ArmVirtPkg/PrePi/PrePi.c
> +++ b/ArmVirtPkg/PrePi/PrePi.c
> @@ -1,6 +1,6 @@
>   /** @file
>   *
> -*  Copyright (c) 2011-2014, ARM Limited. All rights reserved.
> +*  Copyright (c) 2011-2020, ARM Limited. All rights reserved.
>   *
>   *  SPDX-License-Identifier: BSD-2-Clause-Patent
>   *
> @@ -60,16 +60,16 @@ PrePiMain (
>     //
>     InvalidateDataCacheRange((VOID *)(UINTN)PcdGet64 (PcdFdBaseAddress), PcdGet32 (PcdFdSize));
>   
> -  // Initialize MMU and Memory HOBs (Resource Descriptor HOBs)
> -  Status = MemoryPeim (UefiMemoryBase, FixedPcdGet32 (PcdSystemMemoryUefiRegionSize));
> -  ASSERT_EFI_ERROR (Status);
> -
>     // Initialize the Serial Port
>     SerialPortInitialize ();
>     CharCount = AsciiSPrint (Buffer,sizeof (Buffer),"UEFI firmware (version %s built at %a on %a)\n\r",
>       (CHAR16*)PcdGetPtr(PcdFirmwareVersionString), __TIME__, __DATE__);
>     SerialPortWrite ((UINT8 *) Buffer, CharCount);
>   
> +  // Initialize MMU and Memory HOBs (Resource Descriptor HOBs)
> +  Status = MemoryPeim (UefiMemoryBase, FixedPcdGet32 (PcdSystemMemoryUefiRegionSize));
> +  ASSERT_EFI_ERROR (Status);
> +
>     // Create the Stacks HOB (reserve the memory for all stacks)
>     StacksSize = PcdGet32 (PcdCPUCorePrimaryStackSize);
>     BuildStackHob (StacksBase, StacksSize);
> 

We need to check whether this works on Xen - I don't remember whether we 
use some kind of cache coherent shared memory ring there for the serial 
console that only works if the MMU and caches are enabled. Julien?