netdev - Re: [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break ath9k-based AP

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Date:   Fri, 25 Mar 2022 19:15:32 +0100
From:   Toke Høiland-Jørgensen <toke@...e.dk>
To:     Christoph Hellwig <hch@....de>, Halil Pasic <pasic@...ux.ibm.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kalle Valo <kvalo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Olha Cherevyk <olha.cherevyk@...il.com>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break
 ath9k-based AP

Christoph Hellwig <hch@....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