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Message-ID: <50101085cba7fc089339c96f531f797e27c632ff.camel@sipsolutions.net>
Subject: Re: iwlwifi: Regression after migrating to 6.6.32
From: Johannes Berg <johannes@sipsolutions.net>
To: Baochen Qiang <quic_bqiang@quicinc.com>, Fabio Estevam
 <festevam@gmail.com>
Cc: miriam.rachel.korenblit@intel.com, kvalo@kernel.org, Jakub Kicinski
	 <kuba@kernel.org>, linux-wireless <linux-wireless@vger.kernel.org>, 
 linux-kernel <linux-kernel@vger.kernel.org>
Date: Thu, 13 Jun 2024 09:40:26 +0200
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On Thu, 2024-06-13 at 15:10 +0800, Baochen Qiang wrote:
>=20
> On 6/13/2024 3:15 AM, Fabio Estevam wrote:
> > Hi Johannes,
> >=20
> > On Wed, Jun 12, 2024 at 4:10=E2=80=AFPM Johannes Berg <johannes@sipsolu=
tions.net> wrote:
> >=20
> > > Strange. Is there an IOMMU involved on this platform?
> >=20
> > IOMMU isn't available on i.MX8M as far as I know.
> If IOMMU not present, likely the buffer is mapped by SWIOTLB.

Why? The device can do 64-bit DMA, so should be able to just access any
page in the system. Even older devices can do 36-bit DMA, but this is a
newer one. And if IOMMU isn't present, you have no protection anyway.

>  The iova 4215433216, aka 0xFB426800, is 2K aligned, which also supports =
such guessing. See definition of IO_TLB_SIZE.

Not sure that means anything though, I really would have expected a 4k
buffer to be 4k aligned - why would you even want to map it across two
pages?

If it is SWIOTLB, shouldn't we get into this condition?

        /*
         * Historically, swiotlb allocations >=3D PAGE_SIZE were guaranteed=
 to be
         * page-aligned in the absence of any other alignment requirements.
         * 'alloc_align_mask' was later introduced to specify the alignment
         * explicitly, however this is passed as zero for streaming mapping=
s
         * and so we preserve the old behaviour there in case any drivers a=
re
         * relying on it.
         */
        if (!alloc_align_mask && !iotlb_align_mask && alloc_size >=3D PAGE_=
SIZE)
                alloc_align_mask =3D PAGE_SIZE - 1;


Otherwise, not sure though how we could possibly fix this in the driver,
we really shouldn't do dma_set_min_align_mask() since on the TX side we
really have no alignment requirements, and swiotlb_map() uses 0 as
alignment.

johannes