RE: [PATCH RFC 0/3] riscv: Add DMA_COHERENT support

[David Laight]

From: Palmer Dabbelt
> Sent: 03 June 2021 16:39
...
> An example here would be the errata: every system has errata of some
> sort, so if we start flipping off various vendor's errata Kconfigs
> you'll end up with kernels that only function properly on some systems.
> That's fine with me, as long as it's possible to turn on all vendor's
> errata Kconfigs at the same time and the resulting kernel functions
> correctly on all systems.

ISTM that if you can (easily) detect the errata then the detection
should be left it - but the kernel fail to boot if the system
needs the errata fixed.

The same would be needed for DMA in systems with non-coherent memory.

Only a hardware engineer would build a system with non-coherent memory
and without the ability to do uncached accesses and flush/invalidate
small sections of cache.

Mind you we did get a dual-cpu system that didn't have cache-coherency
between the cpus! That was singularly useless.

	David

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