Re: [kernel] powerpc/powernv/ioda2: Reduce upper limit for DMA window size (retry)

On Tue, 2018-09-11 at 05:38:05 UTC, Alexey Kardashevskiy wrote:

We use PHB in mode1 which uses bit 59 to select a correct DMA window.
However there is mode2 which uses bits 59:55 and allows up to 32 DMA
windows per a PE.

Even though documentation does not clearly specify that, it seems that
the actual hardware does not support bits 59:55 even in mode1, in other
words we can create a window as big as 1<<58 but DMA simply won't work.

This reduces the upper limit from 59 to 55 bits to let the userspace know
about the hardware limits.

Fixes: ce57c6610cc2 "Merge branch 'topic/ppc-kvm' into next"
Signed-off-by: Alexey Kardashevskiy <redacted>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/7233b8cab39014620ac9534da11f0f

cheers