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

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Message-ID: <0eee3fd2-7400-7de7-27a7-7fcaa0955854@gmail.com>
Date:   Fri, 16 Oct 2020 12:27:52 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Arnd Bergmann <arnd@...db.de>,
        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 v2 1/2] arm64: dts: broadcom: clear the warnings caused by
 empty dma-ranges

On 10/16/20 11:23 AM, Arnd Bergmann wrote:
> On Fri, Oct 16, 2020 at 6:48 PM Florian Fainelli <f.fainelli@...il.com> wrote:
>> On 10/16/20 4:01 AM, Arnd Bergmann wrote:
>>> On Fri, Oct 16, 2020 at 11:09 AM Zhen Lei <thunder.leizhen@...wei.com> wrote:
>>>>
>>>> Suggested-by: Arnd Bergmann <arnd@...db.de>
>>>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>>>
>>> Acked-by: Arnd Bergmann <arnd@...db.de>
>>>
>>> I see that at least the 'bcd' and 'xhci' devices in fact try to
>>> use 64-bit DMA. It would be good to test this on actual
>>> hardware to ensure that it works correctly when this is enabled.
>>>
>>> Ideally avoiding the swiotlb bounce buffering should only
>>> make it faster here, but there are many chips on which
>>> 64-bit DMA is broken in some form.
>>
>> Is this change really an improvement though? This 'usb' pseudo bus node
>> could just keep being defined with #address-cells = <1> and #size-cells
>> = <1> so as to satisfy the 'reg' definition however we could just adjust
>> dma-ranges to indicate full 64-bit addressing capability. Would not that
>> work?
> 
> When #address-cells is '1', you cannot specify dma-ranges that
> go beyond a 32-bit address range.

Would not it be enough to remove the 'dma-ranges' property though? Sorry
for being slow here.
-- 
Florian