Re: [Buildroot] [PATCH v2 2/2] configs: add raspberrypi 5 defconfig

["Yann E. MORIN" <yann.morin.1998@free.fr>]

Gaël, All,

On 2023-12-11 16:59 +0100, Gaël PORTAY spake thusly:
> This configuration builds an image for the RaspberryPi 5.
> 
> Signed-off-by: Gaël PORTAY <gael.portay@rtone.fr>
[--SNIP--]
> --- /dev/null
> +++ b/configs/raspberrypi5_defconfig
> @@ -0,0 +1,40 @@
> +BR2_aarch64=y
> +BR2_cortex_a76_a55=y
> +BR2_ARM_FPU_VFPV4=y
> +BR2_ARM64_PAGE_SIZE_16K=y

So, we choose 16K for the userland page alignment, because...

[--SNIP--]
> +BR2_LINUX_KERNEL=y
> +BR2_LINUX_KERNEL_CUSTOM_TARBALL=y
> +BR2_LINUX_KERNEL_CUSTOM_TARBALL_LOCATION="$(call github,raspberrypi,linux,17f135b742c4edb340afb365873c3a574f7e16cb)/linux-17f135b742c4edb340afb365873c3a574f7e16cb.tar.gz"
> +BR2_LINUX_KERNEL_DEFCONFIG="bcm2712"

... the bcm2712_defconfig in the kernel tree default to use 16K pages:
    CONFIG_ARM64_16K_PAGES=y

This is all a little bit murky for me, but the kernel help for
CONFIG_ARM64_16K_PAGES states:

  The system will use 16KB pages support. AArch32 emulation
  requires applications compiled with 16K (or a multiple of 16K)
  aligned segments.

But we are not doing 32-on-64 in Buildroot, we're only doing pure
64-bit.

If I interret the kernel help text correctly, aarch64 userland is not
impacted by the page size the kernel uses, so we can still use 4K pages
in userland.

Or do we just want to avoid any confusion at all, and always consider
that the userland and kernel page size must match? Or did I just
misinterpret the kernel help text, and the two *must* match?

If I missed something, or am wrong somewhere, just yell! ;-)

Regards,
Yann E. MORIN.

> +# Build the DTB from the kernel sources
> +BR2_LINUX_KERNEL_DTS_SUPPORT=y
> +BR2_LINUX_KERNEL_INTREE_DTS_NAME="broadcom/bcm2712-rpi-5-b"
> +
> +BR2_LINUX_KERNEL_NEEDS_HOST_OPENSSL=y
> +
> +BR2_PACKAGE_RPI_FIRMWARE=y
> +BR2_PACKAGE_RPI_FIRMWARE_CONFIG_FILE="board/raspberrypi5/config_5.txt"
> +BR2_PACKAGE_RPI_FIRMWARE_CMDLINE_FILE="board/raspberrypi5/cmdline_5.txt"
> +# BR2_PACKAGE_RPI_FIRMWARE_INSTALL_DTB_OVERLAYS is not set
> +
> +# Required tools to create the SD image
> +BR2_PACKAGE_HOST_DOSFSTOOLS=y
> +BR2_PACKAGE_HOST_GENIMAGE=y
> +BR2_PACKAGE_HOST_MTOOLS=y
> +
> +# Filesystem / image
> +BR2_TARGET_ROOTFS_EXT2=y
> +BR2_TARGET_ROOTFS_EXT2_4=y
> +BR2_TARGET_ROOTFS_EXT2_SIZE="120M"
> +# BR2_TARGET_ROOTFS_TAR is not set
> +BR2_ROOTFS_POST_BUILD_SCRIPT="board/raspberrypi5/post-build.sh"
> +BR2_ROOTFS_POST_IMAGE_SCRIPT="board/raspberrypi5/post-image.sh"
> -- 
> 2.43.0
> 
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