[PATCH] ARM: mm: Fix ARCH_LOW_ADDRESS_LIMIT when CONFIG_ZONE_DMA

[Arnd Bergmann]

On Sat, Jun 3, 2023, at 11:06, Stefan Wahren wrote:
> Configuring VMSPLIT_2G + LPAE on Raspberry Pi 4 leads to SWIOTLB
> buffer allocation beyond platform dma_zone_size of SZ_1G, which
> results in broken SD card boot.
>
> So fix this be setting ARCH_LOW_ADDRESS_LIMIT in CONFIG_ZONE_DMA
> case.
>
> Suggested-by: Russell King <linux at armlinux.org.uk>
> Fixes: e9faf9b0b07a ("ARM: add multi_v7_lpae_defconfig")
> Signed-off-by: Stefan Wahren <stefan.wahren at i2se.com>

Reviewed-by: Arnd Bergmann <arnd at arndb.de>

This looks correct and required to me, but I think we also
want the change to paging_init() that you tried earlier before
this patch.

Changing the low address limit by itself makes the swiotlb work
correctly, but for performance we also want to avoid having to
use the swiotlb at all when dealing with the zero page.

      Arnd