Re: [PATCH v2 resend 2/3] arm64: mm: Don't defer reserve_crashkernel() with dma_force_32bit

[Kefeng Wang]

On 2022/4/2 6:09, Vijay Balakrishna wrote:
> On 3/31/2022 12:40 AM, Kefeng Wang wrote:
> > ARM64 enable ZONE_DMA by default, and with ZONE_DMA crash kernel
> > memory reservation is delayed until DMA zone memory range size
> > initilazation performed in zone_sizes_init(), but for most platforms
> > use 32bit dma_zone_bits, so add dma_force_32bit kernel parameter
> > if ZONE_DMA enabled, and initialize arm64_dma_phys_limit to
> > dma32_phys_limit in arm64_memblock_init() if dma_force_32bit
> > is setup, this could let the crash kernel reservation earlier,
> > and allows linear creation with block mapping.
> >
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
>
> I don't see any problem with the approach.  Hope you or someone can 
> test to make sure no surprises on RPi4 with the proposed change.  I do 
> understand on RPi4 --
>
> - both ZONE_DMA and ZONE_DMA32 are enabled
> - one wouldn't use dma_force_32bit kernel parameter
> - crashkernel_could_early_reserve() would return false to preserve 
> late reserve of crash kernel memory
I don't have RPi4, I tested following cases on qemu

1) only with ZONE_DMA

    1.1) only with ZONE_DMA and with dma_force_32bit

2) only with ZONE_DMA32

3) with ZONE_DMA and ZONE_DMA32

   3.1) with ZONE_DMA and ZONE_DMA32 and with dma_force_32bit

> nit --
> - consider renaming crashkernel_could_early_reserve() => 
> crashkernel_early_reserve()
Sure.
> Reviewed-by: Vijay Balakrishna <vijayb@xxxxxxxxxxxxxxxxxxx>
Thanks.