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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>
To:     Robin Murphy <robin.murphy@arm.com>,
        Oleksandr Natalenko <oleksandr@natalenko.name>,
        Christoph Hellwig <hch@lst.de>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Halil Pasic <pasic@linux.ibm.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        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
In-Reply-To: <81ffc753-72aa-6327-b87b-3f11915f2549@arm.com>
References: <1812355.tdWV9SEqCh@natalenko.name>
 <f88ca616-96d1-82dc-1bc8-b17480e937dd@arm.com>
 <20220324055732.GB12078@lst.de> <4386660.LvFx2qVVIh@natalenko.name>
 <81ffc753-72aa-6327-b87b-3f11915f2549@arm.com>
Date:   Thu, 24 Mar 2022 15:27:50 +0100
Message-ID: <878rsza0ih.fsf@toke.dk>
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Robin Murphy <robin.murphy@arm.com> writes:

> On 2022-03-24 10:25, Oleksandr Natalenko wrote:
>> Hello.
>>=20
>> 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
>>>> override to swiotlb_sync_single_for_device() in aa6f8dcbab47, but I th=
ink
>>>> by that point we were increasingly tired and confused and starting to
>>>> second-guess ourselves (well, I was, at least). I don't think it's wro=
ng
>>>> per se, but as I said I do think it can bite anyone who's been doing
>>>> dma_sync_*() wrong but getting away with it until now. If ddbd89deb7d3
>>>> alone turns out to work OK then I'd be inclined to try a partial rever=
t of
>>>> just that one hunk.
>>>
>>> Agreed.  Let's try that first.
>>>
>>> Oleksandr, can you try the patch below:
>>>
>>>
>>> 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,=
 phys_addr_t tlb_addr,
>>>   void swiotlb_sync_single_for_device(struct device *dev, phys_addr_t t=
lb_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=20=20
>>>   void swiotlb_sync_single_for_cpu(struct device *dev, phys_addr_t tlb_=
addr,
>>>
>>=20
>> With this patch the AP works for me.
>
> Cool, thanks for confirming. So I think ath9k probably is doing=20
> something dodgy with dma_sync_*(), but if Linus prefers to make the=20
> above change rather than wait for that to get figured out, I believe=20
> that should be fine.

I'm looking into this; but in the interest of a speedy resolution of the
regression I would be in favour of merging that partial revert and
reinstating it if/when we identify (and fix) any bugs in ath9k :)

-Toke