Re: [PATCH RFC 1/4] of: get dma area lower limit
From: Christoph Lameter (Ampere)
Date: Wed Jan 17 2024 - 17:23:44 EST
On Wed, 27 Dec 2023, Baruch Siach wrote:
of_dma_get_max_cpu_address() returns the highest CPU address that
devices can use for DMA. The implicit assumption is that all CPU
addresses below that limit are suitable for DMA. However the
'dma-ranges' property this code uses also encodes a lower limit for DMA
that is potentially non zero.
All of memory can be used for DMA by default (==ZONE_NORMAL). ZONE_DMA
defines a special range for devices that are unable to perform DMA to all
of memory. Usually due to the lack of address bit support.
So I guess that the platform in question here has as a general limit as to
what address spaces I/O devices can do DMA to?