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

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Date:   Tue, 11 Jul 2017 08:50:34 +0000
From:   Madalin-cristian Bucur <madalin.bucur@....com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        "David S . Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "Arnd Bergmann" <arnd@...db.de>,
        Camelia Alexandra Groza <camelia.groza@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] dpaa_eth: use correct device for DMA mapping API

> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@...db.de]
> Sent: Monday, July 10, 2017 6:14 PM
> Subject: [PATCH] dpaa_eth: use correct device for DMA mapping API
> 
> 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>
> ---
> 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) {
> --
> 2.9.0

Hi Arnd,

Thanks for looking into this, I've tested your fix, it seems to need more work:

[    0.894968]  platform: DMA map failed
[    0.898627]  platform: DMA map failed
[    0.902288]  platform: DMA map failed
[    0.905947]  platform: DMA map failed
[    0.909606]  platform: DMA map failed
[    0.913265]  platform: DMA map failed

You also missed this related change:

@@ -2806,7 +2799,6 @@ static int dpaa_eth_probe(struct platform_device *pdev)
 		dpaa_bps_free(priv);
 bp_create_failed:
 fq_probe_failed:
-dev_mask_failed:
 mac_probe_failed:
 		dev_set_drvdata(dev, NULL);
 		free_netdev(net_dev);

I'll try to address your concern about performing the DMA mapping on a different
device than the one set up by the platform code.

Regards,
Madalin