linux-kernel - Re: [PATCH v2 1/2] arm64: dts: broadcom: clear the warnings caused by empty dma-ranges

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Message-ID: <9c6c6b7e-8c39-8c49-5c87-9b560c027841@broadcom.com>
Date:   Mon, 14 Dec 2020 11:09:07 -0800
From:   Ray Jui <ray.jui@...adcom.com>
To:     Arnd Bergmann <arnd@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>
Cc:     bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Rob Herring <robh+dt@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...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>,
        Bharat Gooty <bharat.gooty@...adcom.com>
Subject: Re: [PATCH v2 1/2] arm64: dts: broadcom: clear the warnings caused by
 empty dma-ranges

+ Bharat

On 11/28/2020 1:58 AM, Arnd Bergmann wrote:
> On Sat, Nov 28, 2020 at 5:53 AM Florian Fainelli <f.fainelli@...il.com> wrote:
>>
>> On Fri, 16 Oct 2020 17:08:32 +0800, Zhen Lei <thunder.leizhen@...wei.com> wrote:
>>> The scripts/dtc/checks.c requires that the node have empty "dma-ranges"
>>> property must have the same "#address-cells" and "#size-cells" values as
>>> the parent node. Otherwise, the following warnings is reported:
>>>
>>> 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)
>>>
>>> Arnd Bergmann figured out why it's necessary:
>>> 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.
>>>
>>> Suggested-by: Arnd Bergmann <arnd@...db.de>
>>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>>> ---
>>
>> Applied to devicetree-arm64/next, thanks!
> 
> The notification may have gone missing, but I had merged it into v5.10-fixes
> already, and as of today, it's in mainline, so you can drop it from your
> next branch, or just leave it in if you want to avoid taking things out of
> your tree.
> 
>       Arnd
> 

It looks like this patch might have caused a regression on Stingray USB.
Bharat, could you please confirm?

The fix would be to properly define the dma-ranges to be 32-bit (0x0 ~
0xffffffff) since IOMMU is disabled on this device and the device's DMA
engine is on a 32-bit bus.

Thanks,

Ray





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