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

[Jonathan Marek]

On 1/16/26 6:19 PM, Bjorn Andersson wrote:
> On Fri, Jan 16, 2026 at 05:53:59PM -0500, Jonathan Marek wrote:
> > It turns out this change will make things worse for the (unfortunately
> > common) EL1+64GB+brokenfirmware case.
> >
> > Because of that I think the Fixes: tag and "(fix 64GB models)" should be
> > dropped from the commit message. (I can also send a v2 with extra info in
> > the commit message if needed)
>
> It seems to me that neither of these to actions will affect the impact
> of the patch. What does "make things worse" imply?

From what Stephan wrote [1]: Without this change, devices that use 
SMMUv3 (PCIe) use bounce buffers for memory outside the 36-bit range. 
With this change they won't use SWIOTLB and it will crash instead. (it 
would still crash for other reasons without this change)

[1] https://patchwork.kernel.org/comment/26681014/

> Are we better off dropping this patch?

This patch gets EL2+64GB (and presumably EL1 as well if OEM provides 
updated EL2 firmware) working without crashes. That's better than having 
all 64GB cases be broken.

> Regards,
> Bjorn
>
> > On 1/16/26 4:39 PM, Bjorn Andersson wrote:
> > > On Thu, 27 Nov 2025 16:29:42 -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.
> > >
> > > Applied, thanks!
> > >
> > > [1/1] arm64: dts: qcom: x1e: bus is 40-bits (fix 64GB models)
> > >         commit: b38dd256e11a4c8bd5a893e11fc42d493939c907
> > >
> > > Best regards,