linux-kernel - Re: [REGRESSION] Recent swiotlb DMA_FROM

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Date:   Fri, 25 Mar 2022 08:12:37 +0100
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        Maxime Bizon <mbizon@...ebox.fr>,
        Toke Høiland-Jørgensen <toke@...e.dk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Halil Pasic <pasic@...ux.ibm.com>,
        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

Hello.

On čtvrtek 24. března 2022 18:07:29 CET Toke Høiland-Jørgensen wrote:
> Right, but is that sync_for_device call really needed? AFAICT, that
> ath9k_hw_process_rxdesc_edma() invocation doesn't actually modify any of
> the data when it returns EINPROGRESS, so could we just skip it? Like
> the patch below? Or am I misunderstanding the semantics here?
> 
> -Toke
> 
> 
> diff --git a/drivers/net/wireless/ath/ath9k/recv.c b/drivers/net/wireless/ath/ath9k/recv.c
> index 0c0624a3b40d..19244d4c0ada 100644
> --- a/drivers/net/wireless/ath/ath9k/recv.c
> +++ b/drivers/net/wireless/ath/ath9k/recv.c
> @@ -647,12 +647,8 @@ static bool ath_edma_get_buffers(struct ath_softc *sc,
>                                 common->rx_bufsize, DMA_FROM_DEVICE);
>  
>         ret = ath9k_hw_process_rxdesc_edma(ah, rs, skb->data);
> -       if (ret == -EINPROGRESS) {
> -               /*let device gain the buffer again*/
> -               dma_sync_single_for_device(sc->dev, bf->bf_buf_addr,
> -                               common->rx_bufsize, DMA_FROM_DEVICE);
> +       if (ret == -EINPROGRESS)
>                 return false;
> -       }
>  
>         __skb_unlink(skb, &rx_edma->rx_fifo);
>         if (ret == -EINVAL) {

With this patch and both ddbd89deb7d3+aa6f8dcbab47 in place the AP works for me.

Thanks.

-- 
Oleksandr Natalenko (post-factum)