netdev - Re: [PATCH 1/2] net: fec: use dma_alloc

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Date:   Mon, 21 Nov 2022 11:24:29 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Greg Ungerer <gerg@...ux-m68k.org>,
        Joakim Zhang <qiangqing.zhang@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        linux-m68k@...ts.linux-m68k.org, uclinux-dev@...inux.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] net: fec: use dma_alloc_noncoherent for m532x

Hi Christoph,

On Mon, Nov 21, 2022 at 10:56 AM Christoph Hellwig <hch@....de> wrote:
> The m532x coldfire platforms can't properly implement dma_alloc_coherent
> and currently just return noncoherent memory from it.  The fec driver
> than works around this with a flush of all caches in the receive path.
> Make this hack a little less bad by using the explicit
> dma_alloc_noncoherent API and documenting the hacky cache flushes.
>
> Signed-off-by: Christoph Hellwig <hch@....de>

Thanks for your patch!

> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -1580,6 +1580,10 @@ fec_enet_rx_queue(struct net_device *ndev, int budget, u16 queue_id)
>         struct page *page;
>
>  #ifdef CONFIG_M532x
> +       /*
> +        * Hacky flush of all caches instead of using the DMA API for the TSO
> +        * headers.
> +        */
>         flush_cache_all();
>  #endif
>         rxq = fep->rx_queue[queue_id];
> @@ -3123,10 +3127,17 @@ static void fec_enet_free_queue(struct net_device *ndev)
>         for (i = 0; i < fep->num_tx_queues; i++)
>                 if (fep->tx_queue[i] && fep->tx_queue[i]->tso_hdrs) {
>                         txq = fep->tx_queue[i];
> +#ifdef CONFIG_M532x

Shouldn't this be the !CONFIG_M532x path?

>                         dma_free_coherent(&fep->pdev->dev,
>                                           txq->bd.ring_size * TSO_HEADER_SIZE,
>                                           txq->tso_hdrs,
>                                           txq->tso_hdrs_dma);
> +#else
> +                       dma_free_noncoherent(&fep->pdev->dev,
> +                                         txq->bd.ring_size * TSO_HEADER_SIZE,
> +                                         txq->tso_hdrs, txq->tso_hdrs_dma,
> +                                         DMA_BIDIRECTIONAL);
> +#endif
>                 }
>
>         for (i = 0; i < fep->num_rx_queues; i++)
> @@ -3157,10 +3168,18 @@ static int fec_enet_alloc_queue(struct net_device *ndev)
>                 txq->tx_wake_threshold =
>                         (txq->bd.ring_size - txq->tx_stop_threshold) / 2;
>
> +#ifdef CONFIG_M532x

Likewise

>                 txq->tso_hdrs = dma_alloc_coherent(&fep->pdev->dev,
>                                         txq->bd.ring_size * TSO_HEADER_SIZE,
>                                         &txq->tso_hdrs_dma,
>                                         GFP_KERNEL);
> +#else
> +               /* m68knommu manually flushes all caches in fec_enet_rx_queue */
> +               txq->tso_hdrs = dma_alloc_noncoherent(&fep->pdev->dev,
> +                                       txq->bd.ring_size * TSO_HEADER_SIZE,
> +                                       &txq->tso_hdrs_dma, DMA_BIDIRECTIONAL,
> +                                       GFP_KERNEL);
> +#endif
>                 if (!txq->tso_hdrs) {
>                         ret = -ENOMEM;
>                         goto alloc_failed;

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds