linux-kernel - Re: [PATCH] dpaa_eth: use correct device for DMA mapping API

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Message-ID: <5cb9b2d7-1512-1bfc-9560-59e17dda40f4@arm.com>
Date:   Mon, 10 Jul 2017 16:55:13 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Arnd Bergmann <arnd@...db.de>,
        Madalin Bucur <madalin.bucur@....com>
Cc:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Camelia Groza <camelia.groza@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dpaa_eth: use correct device for DMA mapping API

On 10/07/17 16:14, Arnd Bergmann wrote:
> Geert Uytterhoeven ran into a build error without CONFIG_HAS_DMA,
> as a result of the driver calling set_dma_ops(). While we can
> fix the build error in the dma-mapping implementation, there is
> another problem in this driver:
> 
> The configuration for the DMA is done by the platform code,
> looking up information about the system from the device tree.
> This copies the information only in an incomplete way, setting
> the dma_map_ops and forcing a specific mask, but ignoring all
> settings regarding IOMMU, coherence etc.
> 
> A better way to avoid the problem is to only ever pass a device
> into the dma_mapping implementation that has been setup by the
> platform code. In this case, that is the parent device, so we
> can get that pointer at probe time. Fortunately, we already have
> a pointer in the device specific structure for that, so we only
> need to modify that.
> 
> Fixes: fb52728a9294 ("dpaa_eth: reuse the dma_ops provided by the FMan MAC device")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Robin Murphy <robin.murphy@....com>

Assuming all the DPAA subcomponents have the same DMA capabilities
(which to the best of my knowledge they probably do), this is a neater
approach than what I started a while back in the context of cleaning up
arch_setup_dma_ops() abuse. FWIW, that looked like this:

----->8-----
diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
index e2ca107f9d94..8eef0db5db30 100644
--- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
+++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
@@ -2539,10 +2539,9 @@ static int dpaa_eth_probe(struct platform_device
*pdev)
        priv->buf_layout[TX].priv_data_size = DPAA_TX_PRIV_DATA_SIZE; /*
Tx */

        /* device used for DMA mapping */
-       arch_setup_dma_ops(dev, 0, 0, NULL, false);
-       err = dma_coerce_mask_and_coherent(dev, DMA_BIT_MASK(40));
+       err = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(40));
        if (err) {
-               dev_err(dev, "dma_coerce_mask_and_coherent() failed\n");
+               dev_err(dev, "dma_set_mask_and_coherent() failed\n");
                goto dev_mask_failed;
        }

diff --git a/drivers/net/ethernet/freescale/fman/mac.c
b/drivers/net/ethernet/freescale/fman/mac.c
index 0b31f8502ada..c81efbfa99c2 100644
--- a/drivers/net/ethernet/freescale/fman/mac.c
+++ b/drivers/net/ethernet/freescale/fman/mac.c
@@ -627,6 +627,10 @@ static struct platform_device
*dpaa_eth_add_device(int fman_id,
        if (ret)
                goto err;

+       ret = of_dma_configure(&pdev->dev, node);
+       if (ret)
+               goto err;
+
        ret = platform_device_add(pdev);
        if (ret)
                goto err;
-----8<-----

We might possibly need to revisit this if and when the question of IOMMU
support in the fsl-mc driver comes up (all this stuff is completely
paged out of my head at the moment, so I'm not certain), but for now I
don't see any reason no to go with your patch.

Robin.

> ---
> Not tested, please see if this works before applying!
> ---
>  drivers/net/ethernet/freescale/dpaa/dpaa_eth.c | 11 ++---------
>  1 file changed, 2 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> index 757b873735a5..f7b0b928cd53 100644
> --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> @@ -2646,14 +2646,6 @@ static int dpaa_eth_probe(struct platform_device *pdev)
>  	priv->buf_layout[RX].priv_data_size = DPAA_RX_PRIV_DATA_SIZE; /* Rx */
>  	priv->buf_layout[TX].priv_data_size = DPAA_TX_PRIV_DATA_SIZE; /* Tx */
>  
> -	/* device used for DMA mapping */
> -	set_dma_ops(dev, get_dma_ops(&pdev->dev));
> -	err = dma_coerce_mask_and_coherent(dev, DMA_BIT_MASK(40));
> -	if (err) {
> -		dev_err(dev, "dma_coerce_mask_and_coherent() failed\n");
> -		goto dev_mask_failed;
> -	}
> -
>  	/* bp init */
>  	for (i = 0; i < DPAA_BPS_NUM; i++) {
>  		int err;
> @@ -2665,7 +2657,8 @@ static int dpaa_eth_probe(struct platform_device *pdev)
>  		dpaa_bps[i]->raw_size = bpool_buffer_raw_size(i, DPAA_BPS_NUM);
>  		/* avoid runtime computations by keeping the usable size here */
>  		dpaa_bps[i]->size = dpaa_bp_size(dpaa_bps[i]->raw_size);
> -		dpaa_bps[i]->dev = dev;
> +		/* DMA operations are done on the platform-provided device */
> +		dpaa_bps[i]->dev = dev->parent;
>  
>  		err = dpaa_bp_alloc_pool(dpaa_bps[i]);
>  		if (err < 0) {
>