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

On Thu, Mar 24, 2022 at 05:29:12PM +0100, Maxime Bizon wrote:

...

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 :)

This looks fishy:

ath9k/recv.c

            /* We will now give hardware our shiny new allocated skb */
            new_buf_addr = dma_map_single(sc->dev, requeue_skb->data,
                                          common->rx_bufsize, dma_type);
            if (unlikely(dma_mapping_error(sc->dev, new_buf_addr))) {
                    dev_kfree_skb_any(requeue_skb);
                    goto requeue_drop_frag;
            }

            /* Unmap the frame */
            dma_unmap_single(sc->dev, bf->bf_buf_addr,
                             common->rx_bufsize, dma_type);

            bf->bf_mpdu = requeue_skb;
            bf->bf_buf_addr = new_buf_addr;

Creating a new mapping for the same buffer before unmapping the previous one does looks rather bogus. But it does not fit the pattern where revering the sync_single changes make the driver work again.