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From:   Oleksandr Natalenko <oleksandr@natalenko.name>
To:     Robin Murphy <robin.murphy@arm.com>, Christoph Hellwig <hch@lst.de>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Halil Pasic <pasic@linux.ibm.com>,
        Christoph Hellwig <hch@lst.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Toke =?ISO-8859-1?Q?H=F8iland=2DJ=F8rgensen?= <toke@toke.dk>,
        Kalle Valo <kvalo@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Olha Cherevyk <olha.cherevyk@gmail.com>,
        iommu <iommu@lists.linux-foundation.org>,
        linux-wireless <linux-wireless@vger.kernel.org>,
        Netdev <netdev@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable <stable@vger.kernel.org>
Subject: Re: [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break ath9k-based AP
Date:   Thu, 24 Mar 2022 11:25:06 +0100
Message-ID: <4386660.LvFx2qVVIh@natalenko.name>
In-Reply-To: <20220324055732.GB12078@lst.de>
References: <1812355.tdWV9SEqCh@natalenko.name> <f88ca616-96d1-82dc-1bc8-b17480e937dd@arm.com> <20220324055732.GB12078@lst.de>
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Hello.

On =C4=8Dtvrtek 24. b=C5=99ezna 2022 6:57:32 CET Christoph Hellwig wrote:
> On Wed, Mar 23, 2022 at 08:54:08PM +0000, Robin Murphy wrote:
> > I'll admit I still never quite grasped the reason for also adding the=20
> > override to swiotlb_sync_single_for_device() in aa6f8dcbab47, but I thi=
nk=20
> > by that point we were increasingly tired and confused and starting to=20
> > second-guess ourselves (well, I was, at least). I don't think it's wron=
g=20
> > per se, but as I said I do think it can bite anyone who's been doing=20
> > dma_sync_*() wrong but getting away with it until now. If ddbd89deb7d3=
=20
> > alone turns out to work OK then I'd be inclined to try a partial revert=
 of=20
> > just that one hunk.
>=20
> Agreed.  Let's try that first.
>=20
> Oleksandr, can you try the patch below:
>=20
>=20
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 6db1c475ec827..6c350555e5a1c 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -701,13 +701,10 @@ void swiotlb_tbl_unmap_single(struct device *dev, p=
hys_addr_t tlb_addr,
>  void swiotlb_sync_single_for_device(struct device *dev, phys_addr_t tlb_=
addr,
>  		size_t size, enum dma_data_direction dir)
>  {
> -	/*
> -	 * Unconditional bounce is necessary to avoid corruption on
> -	 * sync_*_for_cpu or dma_ummap_* when the device didn't overwrite
> -	 * the whole lengt of the bounce buffer.
> -	 */
> -	swiotlb_bounce(dev, tlb_addr, size, DMA_TO_DEVICE);
> -	BUG_ON(!valid_dma_direction(dir));
> +	if (dir =3D=3D DMA_TO_DEVICE || dir =3D=3D DMA_BIDIRECTIONAL)
> +		swiotlb_bounce(dev, tlb_addr, size, DMA_TO_DEVICE);
> +	else
> +		BUG_ON(dir !=3D DMA_FROM_DEVICE);
>  }
> =20
>  void swiotlb_sync_single_for_cpu(struct device *dev, phys_addr_t tlb_add=
r,
>=20

With this patch the AP works for me.

Thanks.

=2D-=20
Oleksandr Natalenko (post-factum)