On Mon, Jun 7, 2021 at 2:51 PM Christoph Hellwig [off-list ref] wrote:

On Mon, Jun 07, 2021 at 02:41:14PM +0800, Guo Ren wrote:

quoted

Double/Triple the size of physical memory regions can't be accepted by
SOC vendors, because it wastes HW resources.
Some cost-down soc interconnects only have 32bit~34bit width of
physical address, are you sure you could force them to expand it? (I
can't)

quoted

or somewhat dynamic.

How can HW implement with dynamic modifying PMA? What's the granularity?

I'm just stating the requirements from the Linux DMA perspective.  You
also do not need tripple the address space, just double.

With double, you only got "strong order + non-cache" for the DMA
descriptor. How about write-combine scenario?

Even, double physical memory address space also wastes HW resources.




--
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/