[PATCH v2] wifi: ath11k: fix IOMMU errors on buffer rings

[Zhenghao Gu]

On Tue, Jan 9, 2024 at 9:41 AM Kalle Valo <kvalo at kernel.org> wrote:
>
> Zhenghao Gu <imguzh at gmail.com> writes:
>
> > virt_to_phys doesn't work on systems with IOMMU enabled,
> > which have non-identity physical-to-IOVA mappings.
>
> Can you give an example of such system? Just curious where you are
> seeing this.

I'm testing on an AMD system with IOMMU enabled in the BIOS and "iommu=nopt"
in the kernel command line. I also noticed
https://bugzilla.kernel.org/show_bug.cgi?id=217056
which may be the same issue.

>
> > It leads to IO_PAGE_FAULTs like this:
> > [IO_PAGE_FAULT domain=0x0023 address=0x1cce00000 flags=0x0020]
> > and no link can be established.
>
> What do you mean with link in this context? Are you talking about 802.11
> association?

Yes.

>
> > This patch changes that to dma_map_single(), which works correctly.
>
> Good catch. And virt_to_phys() documentation even says this:
>
>  *      This function does not give bus mappings for DMA transfers. In
>  *      almost all conceivable cases a device driver should not be using
>  *      this function
>
> > Tested-on: QCN9074 hw1.0 PCI WLAN.HK.2.7.0.1-01744-QCAHKSWPL_SILICONZ-1
> > Signed-off-by: Zhenghao Gu <imguzh at gmail.com>
>
> Jeff, are you ok with this?
>
> I did some cosmetics changes in the pending branch (removed unnecessary
> parenthesis, reverse xmas tree etc), please check:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/commit/?h=pending&id=fefa43d63e1928fce6e8c2bb626900e9ce98ca69