linux-kernel - Re: [PATCH] arm64: dts: qcom: x1e: bus is 40-bits (fix 64GB models)

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Message-ID: <1f2c4e5b-2d7d-41cd-9772-374e3de46a50@oss.qualcomm.com>
Date: Fri, 28 Nov 2025 11:52:04 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Stephan Gerhold <stephan.gerhold@...aro.org>,
        Jonathan Marek <jonathan@...ek.ca>
Cc: linux-arm-msm@...r.kernel.org, Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Sibi Sankar <sibi.sankar@....qualcomm.com>,
        Abel Vesa <abel.vesa@...aro.org>,
        Rajendra Nayak <quic_rjendra@...cinc.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
 <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: qcom: x1e: bus is 40-bits (fix 64GB models)

On 11/28/25 11:26 AM, Stephan Gerhold wrote:
> On Thu, Nov 27, 2025 at 04:29:42PM -0500, Jonathan Marek wrote:
>> Unlike the phone SoCs this was copied from, x1e has a 40-bit physical bus.
>> The upper address space is used to support more than 32GB of memory.
>>
>> This fixes issues when DMA buffers are allocated outside the 36-bit range.
>>
>> Fixes: af16b00578a7 ("arm64: dts: qcom: Add base X1E80100 dtsi and the QCP dts")
>> Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
>> ---
>>  arch/arm64/boot/dts/qcom/x1e80100.dtsi | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/boot/dts/qcom/x1e80100.dtsi b/arch/arm64/boot/dts/qcom/x1e80100.dtsi
>> index cff34d1c74b60..cd34ce5dfd63a 100644
>> --- a/arch/arm64/boot/dts/qcom/x1e80100.dtsi
>> +++ b/arch/arm64/boot/dts/qcom/x1e80100.dtsi
>> @@ -792,8 +792,8 @@ soc: soc@0 {
>>  
>>  		#address-cells = <2>;
>>  		#size-cells = <2>;
>> -		dma-ranges = <0 0 0 0 0x10 0>;
>> -		ranges = <0 0 0 0 0x10 0>;
>> +		dma-ranges = <0 0 0 0 0x100 0>;
>> +		ranges = <0 0 0 0 0x100 0>;
>>  
> 
> Could you clarify which "issues" (crashes?) you are referring to?
> 
> We need to distinguish two distinct use cases here, which are both
> (somewhat) supported upstream: Running in EL1 with the Gunyah hypervisor
> with the regular DTB and in EL2 with the x1-el2.dtbo applied.
> 
> # EL2 with x1-el2.dtbo
> 
> For EL2, I think the 40-bit dma-ranges should indeed work correctly, so
> we could add your proposed change inside x1-el2.dtso. I'm not sure which
> issues we are fixing with that though (besides correctness of the
> hardware description). In EL2, all DMA devices should be behind an
> IOMMU. In this case, the dma-ranges limit the size of the I/O virtual
> addresses (DMA addresses) that are given to the devices. The IOMMU maps
> the DMA buffers to arbitrary physical memory addresses (including
> outside of the 36-bit range, dma-ranges limits only the DMA address).

I've been carrying something similar in my working tree for quite
some time too.. The USB4 PCIe controllers have BAR spaces in the >36b
region, so this will be necessary anyway.

As for the broken-firmware laptops, there's only so much we can do.
A fix for this has been *long* released, but it's up to the OEMs to
pull it in.


I'm not fully sure, but I think certain subsystems still have the 36b
address limitation (camera?), so it would be good to know whether that
needs to be accounted for

Konrad