Re: [PATCH v6 3/4] arm64: use both ZONE_DMA and ZONE_DMA32

[Nicolas Saenz Julienne]

On Mon, 2019-10-21 at 10:15 -0400, Qian Cai wrote:
> > On Sep 11, 2019, at 2:25 PM, Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
> > wrote:
> > 
> > So far all arm64 devices have supported 32 bit DMA masks for their
> > peripherals. This is not true anymore for the Raspberry Pi 4 as most of
> > it's peripherals can only address the first GB of memory on a total of
> > up to 4 GB.
> > 
> > This goes against ZONE_DMA32's intent, as it's expected for ZONE_DMA32
> > to be addressable with a 32 bit mask. So it was decided to re-introduce
> > ZONE_DMA in arm64.
> > 
> > ZONE_DMA will contain the lower 1G of memory, which is currently the
> > memory area addressable by any peripheral on an arm64 device.
> > ZONE_DMA32 will contain the rest of the 32 bit addressable memory.
> > 
> > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
> > Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> > 
> > ---
> 
> With ZONE_DMA=y, this config will fail to reserve 512M CMA on a server,
> 
> https://raw.githubusercontent.com/cailca/linux-mm/master/arm64.config
> 
> CONFIG_DMA_CMA=y
> CONFIG_CMA_SIZE_MBYTES=64
> CONFIG_CMA_SIZE_SEL_MBYTES=y
> CONFIG_CMA_ALIGNMENT=8
> CONFIG_CMA=y
> CONFIG_CMA_DEBUGFS=y
> CONFIG_CMA_AREAS=7
> 
> Is this expected?

Not really, just tested cma=512M on a Raspberry Pi4, and it went well. The only
thing on my build that differs from your config is CONFIG_CMA_DEBUGFS.

Could you post more information on the device you're experiencing this on? Also
some logs.

Regards,
Nicolas

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