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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 12 Jan 2021 10:28:13 -0800
From:   Ray Jui <ray.jui@...adcom.com>
To:     Arnd Bergmann <arnd@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>
Cc:     Bharat Gooty <bharat.gooty@...adcom.com>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Scott Branden <sbranden@...adcom.com>,
        Ray Jui <rjui@...adcom.com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 1/2] arm64: dts: broadcom: clear the warnings caused by
 empty dma-ranges

Hi Arnd,

On 2020-12-15 7:49 a.m., Arnd Bergmann wrote:
> On Tue, Dec 15, 2020 at 4:41 PM Florian Fainelli <f.fainelli@...il.com> wrote:
>>
>> On 12/15/2020 5:19 AM, Bharat Gooty wrote:
>>> Since the IOMMU is disabled and DMA engine is on 32-bit bus, We can not
>>> give the complete DDR for the USB DMA.
>>> So restricting the usable DAM size to 4GB.
>>
>> Thanks, can you make this a proper patch submission along with a Fixes:
>> tag that is:
>>
>> Fixes: 2013a4b684b6 ("arm64: dts: broadcom: clear the warnings caused by
>> empty dma-ranges")
> 
> Yes, that would be helpful, though I would appreciate a better description
> that explains what is actually going on: is it the device or the bus that
> has the 32-bit limitation, and if it is indeed a bug in the device, why do
> you pretend that this is a 64-bit device on a 32-bit bus instead (this
> could also use a comment in the dts file)?
> 
>         Arnd
> 

Sorry for the delay in reply. Bharat finally got time to do some 
investigation to confirm the following:

These USB controllers indeed can address 64-bit. However, on the bus 
internally, only 40-bits are connected to the interconnect of CCN. As a 
result, the 'dma-ranges' should be modified to address 40-bit in size.

We also have a somewhat related question, is it true that since v5.10, 
defining of 'dma-ranges' on the bus node where its child device node has 
implication of IOMMU usage (through 'iommus' or 'iommu-map') is now 
mandatory? My understanding is that the 'dma-ranges' in this scheme will 
define the IOVA address to system address mapping required by all 
devices on that bus. Please help to confirm if my understanding is correct.

Thanks,

Ray

Download attachment "smime.p7s" of type "application/pkcs7-signature" (4151 bytes)