Re: [PATCH v2] arm64: dts: qcom: sdm845: Expand soc bus address range

From: Marc Gonzalez
Date: Thu Jan 17 2019 - 08:41:41 EST

On 16/01/2019 07:49, Bjorn Andersson wrote:

> DMA addresses for devices on the soc bus must be constrained to the 36
> address bits that the bus provides. When no IOMMU is present then this
> is easy--DMA addresses are just physical addresses and physical
> addresses are (by definition) within the address bits of the bus. When
> an IOMMU is present, however, DMA addresses are virtual addresses.
> Despite these addresses being virtual, however, they are still
> constrained by the 36 address bits of the bus.
> Unless dma-ranges is specified, which causes bus_dma_mask to be set, DMA
> allocations for devices on the platform_bus will use all 48 address bits
> available by the ARM SMMU. Causing addresses to be truncated on the bus.
> This patch increases the #size-cells to 2, in order to be able to define
> dma-ranges describe the 36 bit DMA capability of the bus, and bumps

Seems like you changed your mind mid-sentence? :-)

> While touching all reg properties, addresses are padded to 8 digits.