From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Agner Subject: Re: [PATCH] net: fec: check DMA addressing limitations Date: Thu, 02 Aug 2018 09:15:45 +0200 Message-ID: <7d692e8aaefcfec15877a8cd340ee646@agner.ch> References: <20180801114449.21208-1-stefan@agner.ch> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Cc: davem@davemloft.net, krzk@kernel.org, robin.murphy@arm.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Andy Duan Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 02.08.2018 04:00, Andy Duan wrote: > From: Stefan Agner Sent: 2018年8月1日 19:45 >> Check DMA addressing limitations as suggested by the DMA API how-to. >> This does not fix a particular issue seen but is considered good style. >> >> Signed-off-by: Stefan Agner >> --- >> drivers/net/ethernet/freescale/fec_main.c | 6 ++++++ >> 1 file changed, 6 insertions(+) >> >> diff --git a/drivers/net/ethernet/freescale/fec_main.c >> b/drivers/net/ethernet/freescale/fec_main.c >> index c729665107f5..af0fb200e936 100644 >> --- a/drivers/net/ethernet/freescale/fec_main.c >> +++ b/drivers/net/ethernet/freescale/fec_main.c >> @@ -3146,6 +3146,12 @@ static int fec_enet_init(struct net_device >> *ndev) >> fep->tx_align = 0x3; >> #endif >> >> + /* Check mask of the streaming and coherent API */ >> + if (dma_set_mask_and_coherent(&fep->pdev->dev, >> DMA_BIT_MASK(32))) { >> + dev_warn(&fep->pdev->dev, "No suitable DMA available\n"); >> + return -ENODEV; > It is better: > > ret = dma_set_mask_and_coherent(&fep->pdev->dev, DMA_BIT_MASK(32)); > if (ret < 0) { > dev_warn(&fep->pdev->dev, "No suitable DMA available\n"); > return ret; > } The code comes from the example in Documentation/DMA-API-HOWTO.txt. I can rearrange if you prefer. > > > If the patch aim to "OF: Don't set default coherent DMA mask", I think > not only this driver need to add the DMA mask limitations, many other > drivers also need. It doesn't exactly address the issue since with that patch DMA mask wasn't set at all. This code would just make the driver fail with -ENODEV instead of -ENOMEM. To force a DMA mask I would have to set the DMA mask using dma_coerce_mask_and_coherent(). But as discussed with Robin it is safe to assume that an initial mask is set by the bus code: http://lkml.kernel.org/r/892f9d14-e6fd-7b1b-d07b-af0be6e623fa@arm.com Setting the DMA mask on DT buses has been addressed by Robin with "of/platform: Initialise default DMA masks". So everything should be fine again. I agree, other drivers need fixing too. -- Stefan > > >> + } >> + >> fec_enet_alloc_queue(ndev); >> >> bd_size = (fep->total_tx_ring_size + fep->total_rx_ring_size) * dsize; >> -- >> 2.18.0