Messages in this thread | | | Subject | Re: [PATCH 1/2] arm64: dts: broadcom: remove an unused property dma-ranges | From | "Leizhen (ThunderTown)" <> | Date | Wed, 14 Oct 2020 21:36:03 +0800 |
| |
On 2020/10/14 15:38, Arnd Bergmann wrote: > On Wed, Oct 14, 2020 at 5:15 AM Florian Fainelli <f.fainelli@gmail.com> wrote: >> On 10/12/2020 11:06 PM, Zhen Lei wrote: >>> stingray-usb.dtsi is finally included by three dts files: >>> bcm958802a802x.dts, bcm958742k.dts and bcm958742t.dts. I searched all >>> these three entire expanded dts files, and each of them contains only one >>> dma-ranges. No conversion range is specified, so it cannot work properly. >>> I think this property "dma-ranges" is added by mistake, just remove it. >>> Otherwise, the following error will be reported when any YAML detection >>> is performed on arm64. >>> >>> arch/arm64/boot/dts/broadcom/stingray/stingray-usb.dtsi:7.3-14: Warning \ >>> (dma_ranges_format): /usb:dma-ranges: empty "dma-ranges" property but \ >>> its #address-cells (1) differs from / (2) >>> arch/arm64/boot/dts/broadcom/stingray/stingray-usb.dtsi:7.3-14: Warning \ >>> (dma_ranges_format): /usb:dma-ranges: empty "dma-ranges" property but \ >>> its #size-cells (1) differs from / (2) >>> >>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> >> >> This looks fine to me, Scott, Ray do you want to Ack this patch before I >> take it? > > Does it mean that there are no devices on this bus that can do DMA? > > Usually there should be a dma-ranges property to identify that DMA > is possible and what the limits are, though we have failed to enforce > that.
Documentation/devicetree/bindings/iommu/iommu.txt +79 When an "iommus" property is specified in a device tree node, the IOMMU will be used for address translation. If a "dma-ranges" property exists in the device's parent node it will be ignored. An exception to this rule is if the referenced IOMMU is disabled, in which case the "dma-ranges" property of the parent shall take effect.
The dma-ranges is only required by IOMMU disabled case. And should exist in the parent node of IOMMU device. But this deleted dma-ranges is under the usb bus node.
> > Also note that the #address-cells=<1> means that any device under > this bus is assumed to only support 32-bit addressing, and DMA will > have to go through a slow swiotlb in the absence of an IOMMU.
The dma_alloc_coherent() will allocate memory with GFP_DMA32 flag and try the 0-4G first. The reserved swiotlb buffer memory is used only when the allocation failed.
memory@80000000: device_type: ["memory"] reg: [[0x0, 0x80000000, 0x0, 0x80000000], [0x8, 0x80000000, 0x1, 0x80000000]]
If this is the actual physical memory size, the #address-cells should be set to <1>.
> > Arnd > > . >
| |