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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>
To:     Christoph Hellwig <hch@lst.de>, Halil Pasic <pasic@linux.ibm.com>
Cc:     Robin Murphy <robin.murphy@arm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleksandr Natalenko <oleksandr@natalenko.name>,
        Christoph Hellwig <hch@lst.de>,
        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: <20220325163204.GB16426@lst.de>
References: <1812355.tdWV9SEqCh@natalenko.name>
 <CAHk-=wiwz+Z2MaP44h086jeniG-OpK3c=FywLsCwXV7Crvadrg@mail.gmail.com>
 <27b5a287-7a33-9a8b-ad6d-04746735fb0c@arm.com>
 <CAHk-=wip7TCD_+2STTepuEZvGMg6wcz+o=kyFUvHjuKziTMixw@mail.gmail.com>
 <f88ca616-96d1-82dc-1bc8-b17480e937dd@arm.com>
 <20220324190216.0efa067f.pasic@linux.ibm.com>
 <20220325163204.GB16426@lst.de>
Date:   Fri, 25 Mar 2022 19:15:32 +0100
Message-ID: <87y20x7vaz.fsf@toke.dk>
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Christoph Hellwig <hch@lst.de> writes:

> On Thu, Mar 24, 2022 at 07:02:16PM +0100, Halil Pasic wrote:
>> > If 
>> > ddbd89deb7d3 alone turns out to work OK then I'd be inclined to try a 
>> > partial revert of just that one hunk.
>> >
>> 
>> I'm not against being pragmatic and doing the partial revert. But as
>> explained above, I do believe for correctness of swiotlb we ultimately
>> do need that change. So if the revert is the short term solution,
>> what should be our mid-term road-map?
>
> Unless I'm misunderstanding this thread we found the bug in ath9k
> and have a fix for that now?

According to Maxim's comment on the other subthread, that ath9k patch
wouldn't work on all platforms (and constitutes a bit of a violation of
the DMA API ownership abstraction). So not quite, I think?

-Toke