[linux-sunxi] Re: [PATCH 6/9] sunxi: allow 32-bit builds for 64-bit SoCs

[Andre Przywara]

Hi Alex,

On 2/22/19 2:13 AM, Alexander Graf wrote:


On 21.02.19 02:30, Andre Przywara wrote:
At the moment we build the SPL and U-Boot proper for the 64-bit AArch64
instruction set. But since the cores provide an AArch32 compatibility mode
and in fact the BootROM runs in 32-bit mode, it can be useful to have at
least the SPL run in AArch32 as well. This has two advantages:
- As AArch32 features the compact Thumb2 instruction encoding, we can
   get a much smaller image size, which is a relief for our SPL.
- Staying in AArch32, with the MMU turned off, allows an easy return to
   the BootROM and its FEL mode. This enables FEL booting on those SoCs.

Introduce a Kconfig option which toggles between CONFIG_ARM64 and
CONFIG_CPU_V7A, to allow easy switching between the two modes. This can
be manually selected in menuconfig, but follow-up patches will introduce
a separate defconfig for that purpose.

Signed-off-by: Andre Przywara <andre.przyw...@arm.com>
---
  arch/arm/mach-sunxi/Kconfig | 13 ++++++++++---
  1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/arm/mach-sunxi/Kconfig b/arch/arm/mach-sunxi/Kconfig
index 74e234cded..347d737fd0 100644
--- a/arch/arm/mach-sunxi/Kconfig
+++ b/arch/arm/mach-sunxi/Kconfig
@@ -146,6 +146,10 @@ config SUNXI_DRAM_MAX_SIZE
        default 0xC0000000 if MACH_SUN50I || MACH_SUN50I_H5 || MACH_SUN50I_H6
        default 0x80000000
  
+config SUNXI_ARMV8_32BIT_BUILD
+       bool "Build 32-bit binaries for ARMv8 SoCs"
+       default n
+
  choice
        prompt "Sunxi SoC Variant"
        optional
@@ -275,7 +279,8 @@ config MACH_SUN9I
  
  config MACH_SUN50I
        bool "sun50i (Allwinner A64)"
-       select ARM64
+       select ARM64 if !SUNXI_ARMV8_32BIT_BUILD

Can't you make this "imply ARM64" instead and then just set
ARM64=n;CPU_V7A=y in the defconfig?

Ha, that indeed sounds tempting, and actually I tried this before, but 
it doesn't work. The kernel doc says that an "imply" setting can be 
overwritten by a direct dependency or a visible prompt. ARM64 is not 
visible (empty bool), so I figured that introducing this simple symbol 
is the smallest pain to tackle this issue.

Cheers,
Andre.


Alex

+       select CPU_V7A if SUNXI_ARMV8_32BIT_BUILD
        select DM_I2C
        select PHY_SUN4I_USB
        select SUN6I_PRCM
@@ -291,14 +296,16 @@ config MACH_SUN50I
  
  config MACH_SUN50I_H5
        bool "sun50i (Allwinner H5)"
-       select ARM64
+       select ARM64 if !SUNXI_ARMV8_32BIT_BUILD
+       select CPU_V7A if SUNXI_ARMV8_32BIT_BUILD
        select MACH_SUNXI_H3_H5
        select FIT
        select SPL_LOAD_FIT
  
  config MACH_SUN50I_H6
        bool "sun50i (Allwinner H6)"
-       select ARM64
+       select ARM64 if !SUNXI_ARMV8_32BIT_BUILD
+       select CPU_V7A if SUNXI_ARMV8_32BIT_BUILD
        select SUPPORT_SPL
        select FIT
        select SPL_LOAD_FIT


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