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

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Date:   Thu, 1 Dec 2022 15:41:34 +1000
From:   Greg Ungerer <gerg@...ux-m68k.org>
To:     Christoph Hellwig <hch@....de>,
        Joakim Zhang <qiangqing.zhang@....com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        "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 21/11/22 19:56, Christoph Hellwig 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>
> ---
>   drivers/net/ethernet/freescale/fec_main.c | 19 +++++++++++++++++++
>   1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
> index 28ef4d3c18789..5230698310b5e 100644
> --- 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
>   			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
>   		txq->tso_hdrs = dma_alloc_coherent(&fep->pdev->dev,
>   					txq->bd.ring_size * TSO_HEADER_SIZE,
>   					&txq->tso_hdrs_dma,
>   					GFP_KERNEL);

Even with this corrected this will now end up failing on all other ColdFire types
with the FEC hardware module (all the non-M532x types) once the arch_dma_alloc()
returns NULL.

Did you mean "ifndef CONFIG_COLDFIRE" here?


> +#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;

And what about the dmam_alloc_coherent() call in fec_enet_init()?
Does that need changing too?

Regards
Greg