Re: [PATCH v2 4/5] ARM: Add basic support for Airoha EN7523 SoC

Hi Arnd,

On Tue, 7 Sept 2021 at 23:12, Arnd Bergmann [off-list ref] wrote:

quoted

I think the broken memory controller is still there so somehow I'd
need to get the heavy barrier to work in arm64. I haven't yet worked
out if that's even possible.

I think I missed that part of the discussion, or I forgot about it already.
What is the issue you are referring to here?

Sorry. I should have put a bit more context. This is for the SSD268G
not the original target of this series. But a similar situation.
The SSD268G (according to the decompiled device tree) is the same
hardware as the MSTAR_V7 chips but with a Cortex A53 instead of the
Cortex A7.
So it probably has the same memory controller as the MSTAR_V7 stuff
and that memory controller is not coherent so it needs the kernel to
make sure memory requests are flushed out to memory before DMA
happens[0]. For arm I fixed that with the heavy mb callback. With
arm64 I have no idea how to fix that.

I'm interested to see how this Airoha EN7523 series goes as if/when I
push anything for the SSD268G it'll probably only be for a 32bit
kernel.

0 - https://elixir.bootlin.com/linux/latest/source/arch/arm/mach-mstar/mstarv7.c#L61