Re: [PATCH v3 06/16] ArmPkg/ArmLib: add support for reading the max physical address space size

[Laszlo Ersek <lersek@redhat.com>]

On 11/28/18 15:33, Ard Biesheuvel wrote:
> Add a helper function that returns the maximum physical address space
> size as supported by the current CPU.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  ArmPkg/Include/Library/ArmLib.h               |  6 ++++++
>  ArmPkg/Library/ArmLib/AArch64/ArmLibSupport.S | 17 +++++++++++++++++
>  ArmPkg/Library/ArmLib/Arm/ArmLibSupport.S     |  8 ++++++++
>  ArmPkg/Library/ArmLib/Arm/ArmLibSupport.asm   |  8 ++++++++
>  4 files changed, 39 insertions(+)
> 
> diff --git a/ArmPkg/Include/Library/ArmLib.h b/ArmPkg/Include/Library/ArmLib.h
> index ffda50e9d767..9a804c15fdb6 100644
> --- a/ArmPkg/Include/Library/ArmLib.h
> +++ b/ArmPkg/Include/Library/ArmLib.h
> @@ -733,4 +733,10 @@ ArmWriteCntvOff (
>    UINT64   Val
>    );
>  
> +UINTN
> +EFIAPI
> +ArmGetPhysicalAddressBits (
> +  VOID
> +  );
> +
>  #endif // __ARM_LIB__
> diff --git a/ArmPkg/Library/ArmLib/AArch64/ArmLibSupport.S b/ArmPkg/Library/ArmLib/AArch64/ArmLibSupport.S
> index 1ef2f61f5979..b7173e00b039 100644
> --- a/ArmPkg/Library/ArmLib/AArch64/ArmLibSupport.S
> +++ b/ArmPkg/Library/ArmLib/AArch64/ArmLibSupport.S
> @@ -196,4 +196,21 @@ ASM_FUNC(ArmWriteSctlr)
>  3:msr   sctlr_el3, x0
>  4:ret
>  
> +ASM_FUNC(ArmGetPhysicalAddressBits)
> +  mrs   x0, id_aa64mmfr0_el1
> +  adr   x1, .LPARanges
> +  and   x0, x0, #0xf
> +  ldrb  w0, [x1, x0]
> +  ret
> +
> +//
> +// Bits 0..3 of the AA64MFR0_EL1 system register encode the size of the
> +// physical address space support on this CPU:
> +// 0 == 32 bits, 1 == 36 bits, etc etc
> +// 7 and up are reserved
> +//
> +.LPARanges:
> +  .byte 32, 36, 40, 42, 44, 48, 52,  0
> +  .byte  0,  0,  0,  0,  0,  0,  0,  0
> +
>  ASM_FUNCTION_REMOVE_IF_UNREFERENCED
> diff --git a/ArmPkg/Library/ArmLib/Arm/ArmLibSupport.S b/ArmPkg/Library/ArmLib/Arm/ArmLibSupport.S
> index f2a517671f0a..0e9f9d0453e4 100644
> --- a/ArmPkg/Library/ArmLib/Arm/ArmLibSupport.S
> +++ b/ArmPkg/Library/ArmLib/Arm/ArmLibSupport.S
> @@ -165,4 +165,12 @@ ASM_FUNC(ArmWriteCpuActlr)
>    isb
>    bx      lr
>  
> +ASM_FUNC (ArmGetPhysicalAddressBits)
> +  mrc     p15, 0, r0, c0, c1, 4   // MMFR0
> +  and     r0, r0, #0xf            // VMSA [3:0]
> +  cmp     r0, #5                  // >= 5 implies LPAE support
> +  movlt   r0, #32                 // 32 bits if no LPAE
> +  movge   r0, #40                 // 40 bits if LPAE
> +  bx      lr
> +
>  ASM_FUNCTION_REMOVE_IF_UNREFERENCED
> diff --git a/ArmPkg/Library/ArmLib/Arm/ArmLibSupport.asm b/ArmPkg/Library/ArmLib/Arm/ArmLibSupport.asm
> index 219140c22b13..3eb52875971d 100644
> --- a/ArmPkg/Library/ArmLib/Arm/ArmLibSupport.asm
> +++ b/ArmPkg/Library/ArmLib/Arm/ArmLibSupport.asm
> @@ -169,4 +169,12 @@
>    isb
>    bx      lr
>  
> + RVCT_ASM_EXPORT ArmGetPhysicalAddressBits
> +  mrc     p15, 0, r0, c0, c1, 4   ; MMFR0
> +  and     r0, r0, #0xf            ; VMSA [3:0]
> +  cmp     r0, #5                  ; >= 5 implies LPAE support
> +  movlt   r0, #32                 ; 32 bits if no LPAE
> +  movge   r0, #40                 ; 40 bits if LPAE
> +  bx      lr
> +
>    END
> 

I didn't review the assembly code, but formally, the patch looks OK to me.

Acked-by: Laszlo Ersek <lersek@redhat.com>