linux-kernel - Re: [PATCH 1/2] arm64: dts: broadcom: remove an unused property dma-ranges

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Date:   Wed, 14 Oct 2020 09:38:18 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Zhen Lei <thunder.leizhen@...wei.com>,
        Rob Herring <robh+dt@...nel.org>, Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] arm64: dts: broadcom: remove an unused property dma-ranges

On Wed, Oct 14, 2020 at 5:15 AM Florian Fainelli <f.fainelli@...il.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@...wei.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.

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.

      Arnd