Re: [PATCH] nvme/pci: Use host managed power state for suspend

[Christoph Hellwig]

On Mon, May 13, 2019 at 06:01:39PM +0000, Mario.Limonciello@xxxxxxxx wrote:
> When using HMB the SSD will be writing to some memory mapped region.
> Writing to
> that region would use DMA to access host memory, no?

Memory mapped region?  It will use the devices DMA engine to write
host memory, which we explicitly allowed it.

> If the DMA controller is not functional writing to that region won't work properly as 
> it can't access that memory.

The DMA controller is in the device.  External DMA controllers are only
used on very low-end periphals, usually cheap IP blocks like SPI
controllers or similar.